Manual of Surface Weather Observation Standards (MANOBS) 8th Edition, Amendment 2

Manual of Surface Weather Observation Standards
Eighth Edition, Amendment 2
February 2023

Foreword

The Manual of Surface Weather Observations Standards (MANOBS), Eighth Edition, has been prepared with due consideration to the standards and recommendations set down by the World Meteorological Organization (WMO) and, for the aeronautical portions, by the International Civil Aviation Organization (ICAO) and Canadian Aviation Regulations (CARs). The standards set out in MANOBS do not inhibit agencies from doing more than is specified.

Manual conventions

Throughout this manual:

• The term “shall” or “shall not” indicates that compliance with a standard is mandatory
• All references to miles (mi.) are references to the international statute mile (precisely equal to 1.609344 km)
• All reference for clouds based height are in feet (precisely equal to 0.3048 meters)
• All reference for wind speed are in knots (precisely equal to 1.852 km/h)

The following typographical and stylistic conventions are used throughout this manual:

• Code forms, symbolic letters and code figures have been printed in 14 point dark blue Courier New font
• Notes have been printed in medium grey-shaded boxes, preceded by the word “Note” in bold
• Blank table cells have been marked with an en-dash “–” to indicate to assistive technology users that these cells may be ignored

Amendments

Amendments will be issued when warranted, and a review will take place in conjunction with amendments to relevant WMO and ICAO standards. All holders of paper copies of the manual are responsible for keeping their copies current. When amendments are entered in the manual, they should be recorded on the page headed “Record of amendments.”

The version of the Manual found published on the Meteorological Service of Canada website, in either official language, shall be considered to be the official version.

Changes, additions, deletions, and corrections will be issued as necessary solely by the Meteorological Service of Canada after consultation and coordination with the working group (Transport Canada, NAV CANADA and the Departement of National Defence) responsible for MANOBS.

Inquiries

Inquiries about the content of this manual should be directed to the Assistant Deputy Minister (ADM), Meteorological Service of Canada, through appropriate channels.

Application

MANOBS is applicable to stations taking the following types of observations:

• Staffed: Stations where surface weather observers are responsible for the meteorological observations
• Automated: Stations where surface weather observing systems are implemented to prepare the requisite meteorological reports for transmission, without a weather observer being present

Observing procedures

With the publication of the Eighth Edition, procedures and practices specific to weather observing have been removed from MANOBS. Individual service providers shall issue their own manuals setting out their weather observing procedures and practices which implement the MANOBS standards. Such manuals shall complement, not supersede, the standards contained in MANOBS, Eighth Edition.

Pilot reports (PIREP)

Pilot reports are no longer part of MANOBS. The responsibility for publishing procedures for PIREPS now resides with individual service providers (NAV CANADA and Department of National Defence).

Editor's remarks

This manual has been edited to be consistent with the Government of Canada’s brand guidelines, and best practices for accessibility (Web Content Accessibility Guidelines 2.0), as well as the design and structural requirements of the Canada.ca Content Style Guide.

Record of amendments

Record of amendments

Number	Effective date	Entered by	Date of entry
1	December 2021	Sylvain Pelletier	December 2021
2	February 2023	Sylvain Pelletier	February 2023

Record of revisions

Significant and substantial revisions to MANOBS Eighth Edition are listed below with a description of the changes. The Record of revisions is updated whenever amendments are issued.

Record of revisions

Section	Revision description	Effective date
Foreword	Replaced abbreviation "PIREPS" - "PIREP" to match MANAB	February 2023
3.3.6	Paragraph 3) Replaced remark abbreviation "ESTD" - "EST" to match MANAB	February 2023
3.4	Replaced remark abbreviation "ESTD" - "EST" to match MANAB	February 2023
4.6	Replaced remark abbreviation "IMPRG" - "IMPR" & "DRFTG" - "DRFT" to match MANAB	February 2023
6.4.3	Replaced remark abbreviation "OVRHD" - "OHD" to match MANAB	February 2023
6.5.2	Paragraph 1), 3), replaced remark abbreviation "CONTUS" - "CONS" to match MANAB	February 2023
6.5.3	Second example, replaced "6" by "7" to remove any ambiguity	February 2023
6.6.1.1.1	Removed "ice pellets showers"	February 2023
6.7.4	Reworded the first sentence for "Fog patches"  to remove any ambiguity	February 2023
7.3.5	Replaced remark abbreviation "XTNDG" - "EXTD" to match MANAB	February 2023
7.4	Removed "ice pellets showers"in table 7-4	February 2023
11.2.3.7	Removed "ice pellets showers". Added small hailstones to the list.	February 2023
12.2.3.1	Correction to para 4 to point to the correct reference	February 2023
12.2.3.2	Replaced remark abbreviation "ALL QUADS" - "ALQDS" to match MANAB	February 2023
13.2.9	Reworded the definition of "Fog patches:" to remove any ambiguity	February 2023
13.2.14	Added "small hailstones" as a separate bullet. Removed the description for ice pellets showers	February 2023
15.3.4.1.1	Correction to table 15-7 to reflect the correct values for N and Nh	February 2023
15.3.12.2	Removed "SHPL" in figure 15-1	February 2023
15.3.12.2.2	Removed the word "(non-showery)" for code figure 23 to comply with WMO. Removed the word "ice pellets" for code figure 27 to comply with WMO. Removed the word (non-showery) for Note(4) since only one type of ice pellets	February 2023
15.3.12.2.2	Removed the word "(non-showery)" for code figure 79 to comply with WMO	February 2023
15.3.12.2.2	Reworded Code figure 87 and 88 to reflect "small hail" as per WMO. Removed the word "ice pellets" for code figure 93, 94 and 96 to comply with WMO	February 2023
15.3.12.3	Removed "SHPL" to table 15-19	February 2023
15.3.12.3.5	Replaced example 7 and 8 to depict better the use of code 7wwW1W2 and 909Rtdc when ww code figure is 29	February 2023
15.3.12.3.5	Replaced Tenths to Oktas in examples 9, 11-14 and 17-18	February 2023
Appendix 2	Removed "Ice Pellets Showers"and added "Small hailstones" under Tornadoes, Thunderstorms and Precipitation section	February 2023
Appendix 2	Added "Volcanic Ash" under Obstruction to Vision (visibility 6 mi. or less) section	February 2023

Part A Standards for weather observing programs

Chapter 1. Introduction

1.1 General information

This chapter contains information on the legal authority for meteorological and aeronautical matters, as well as the application of that authority as set out in MANOBS and related publications. Information on the World Meteorological Organization and synoptic reports is also provided.

1.2 Meteorological authority

In accordance with the Department of Environment Act, the Minister of Environment and Climate Change Canada has delegated to the Assistant Deputy Minister for the Meteorological Service of Canada the meteorological authority for Canada for all matters related to the WMO. Throughout this manual, the initialism “ADM” is used to refer to the Assistant Deputy Minister for the Meteorological Service of Canada.

All statements made in this manual shall be regarded as authoritative and shall be considered by the weather service provider and weather observers to be requirements and standards for surface weather observing programs.

1.3 Aeronautical authority

The Minister of Environment and Climate Change Canada is assigned all powers, duties and functions for all meteorological matters over which Parliament has jurisdiction that are not assigned by law to another department. Under the Aeronautics Act and Canadian Aviation Regulations, responsibility for the safety, regularity and efficiency of Canada's civil air transportation systems, including aviation weather services, rests with the Minister of Transport.

In accordance with the Aeronautics Act, the Minister of Transport has delegated the meteorological authority for matters related to civil aeronautical meteorology to the Director of Standards, Civil Aviation Directorate. Matters related to Canadian Forces meteorology and oceanography are the responsibility of the Minister of Defence.

The aeronautical standards set out in this manual shall be considered in conjunction with the standards contained in International Civil Aviation Organization (ICAO) Annex 3, Meteorological Service for International Air Navigation, and in the Manual of Standards and Procedures for Aviation Weather Forecasts (MANAIR) as referenced by Canadian Aviation Regulations 804.01 (1) subparagraphs (a) and (b), respectively. Any reference to the standards contained in Annex 3 also includes the differences notified to ICAO in respect of those standards by the Government of Canada in accordance with Canadian Aviation Regulations 800.01 (2).

1.3.1 Joint standards documents

Environment and Climate Change Canada and Transport Canada, each having an interest in the standards applicable to aviation weather observing and forecasting, agree that the Manual of Standards for Aviation Weather Forecasts (MANAIR) and the Manual of Surface Weather Observations (MANOBS) are joint documents.

Standards within MANOBS, except for those found in Part B, are regulatory standards which are referenced in aviation safety regulations. As such, changes to these sections of MANOBS are subject to the consultation process established by the Minister of Transport for regulatory standards. Where necessary due to urgent or safety related matters, an amendment may precede the consultation process, subject to the concurrence of the meteorological authority.

In accordance with Article 37 of the International Convention on Civil Aviation, Canada has agreed to collaborate on achieving the highest practicable degree of uniformity in the regulations, standards, and procedures related to the collection and exchange of meteorological information.

When provisions set out in MANOBS are rendered obsolete or superseded by revisions to ICAO Annex 3, the required amendments to MANOBS can be made without further consultation, subject to the concurrence of the meteorological authority.

The details of Canadian state differences to Annex 3 are published in the state aeronautical information publication (AIP), AIP Canada (ICAO), which is available on the NAV CANADA website. Canadian state differences to the WMO Manual on Codes are published in WMO No. 306, Volume II.

In the event of real or apparent conflict between MANOBS and ICAO Annex 3, the provisions of either are permissible, and an amendment to MANOBS and/or a Canadian state difference will be expedited.

MANOBS includes a separate synoptic section, Part B, “Standards for synoptic observations and reports,” referencing WMO Manual on Codes No. 306, Volume I.1, FM 12-XI SYNOP. Part B is not used as a regulatory document referenced in aviation safety regulations. As such, amendments to Part B in MANOBS are not subject to the consultation process established by the Minister of Transport for regulatory standards.

1.3.2 Application

For aeronautical purposes, the observation standards in this manual are applicable to all meteorological reports to aviation other than those used exclusively for local visual flight rules or as otherwise permitted by the Canadian Aviation Regulations or exemptions thereto. Otherwise, all meteorological reports for aeronautical purposes shall comply with the requirements of MANOBS in accordance with Canadian Aviation Regulations 804.01 (1) (c). It is the responsibility of a service provider to furnish the necessary resources and to be accountable for compliance with regulatory standards.

1.4 World Meteorological Organization

Weather recognizes no international boundaries. A precise synoptic picture of weather conditions over a vast area of the earth’s surface is required in order to provide national and international forecasts and climatological data to satisfy the needs of aviation, agriculture, industry and the public. As a first step in meeting these requirements, surface weather reports are prepared and exchanged throughout the world in an international code developed and agreed upon by member states of the World Meteorological Organization. Such reports are generally made at least four times daily, and a complete report may contain over 20 pieces of information including measurements of atmospheric pressure, which are calculated from barometer readings taken at precisely the same time throughout the world (i.e., 0000 UTC, 0600 UTC, 1200 UTC and 1800 UTC). These observations are referred to as synoptic observations.

The international meteorological code FM 12-IX SYNOP is used for reporting synoptic surface observations from a land station, either staffed or automatic. The common synoptic code comprises six sections numbered 0 to 5, each of which is primarily composed of five-figure code groups. Most groups in sections 0 to 5 begin with a numerical indicator and these indicators are numbered consecutively within each section. The numerical indicators identify a specific group which always contains the same weather elements. Thus the omission, whether accidental or deliberate, of any one group will not affect the identification of other groups. Indeed, provision is made within the code for omission of groups when their weather elements are either not present or cannot be observed. This also ensures that the code is flexible enough for both staffed and automatic stations.

Chapter 2. Surface weather observing program standards

2.1 General information

The purpose of routine aeronautical weather observations is to provide detailed information on current weather for aviation and aviation forecasting. Records of weather observations have both immediate and long-term value. Information obtained from aeronautical weather observations is also used for public forecasts, building codes, climatological data and other weather related purposes.

A surface weather observation is a quantitative or qualitative evaluation by instrumental or visual means of one or more meteorological elements at a place at a given time.

A surface weather report is a statement, presented in plain language or in code, either orally, in written form or by telecommunication, of past or present meteorological conditions at a place at a given time.

This chapter is meant to introduce aviation weather observing program staff to the general standards and requirements of weather observing programs. This chapter contains information on sensor siting, types of staffed and automated observations, reference points for observations, standard parameters to be observed, and times and schedules of observations.

2.2 Quality Assurance Management System (QAMS)

Notification

Each aviation weather service provider shall provide notification to the Minister of Transport (who, hereinafter, may be referred to as ‘TC’ for Transport Canada) pertaining to their services and inform the Minister of any changes to this information. This shall include:

• The name, address and telephone number (and e-mail address, as applicable) of the service provider (The person named is responsible for all aspects of the service being provided and is liable for meeting all requirements);
• The aerodrome or meteorological station, its elevation and the elevation of any pressure sensor with reference to a survey result or benchmark and its geographical coordinates, where the meteorological reports originate;
• A summary description of the service to be provided including specification of the meteorological elements to be reported;
• Method(s) by which meteorological reports will be disseminated;
• The schedule (including specification of an ‘on request’ basis, as applicable), at which meteorological reports will be provided

Subject to section 803.01 of the Canadian Aviation Regulations, a service provider shall notify TC and NAV CANADA in advance of commencing to provide these services or making changes to services already being provided.

The service provider shall immediately notify NAV CANADA and the appropriate air traffic services units of any change to the service being provided, including if they are discontinued, if that service is used to permit the execution of an instrument procedure that is published in the Canada Air Pilot.

It is the responsibility of the service provider to develop and maintain all documentation necessary in support of QAMS.

The service provider shall establish, document, implement and maintain a quality management system comprising the procedures, processes and resources necessary to provide for quality management of the meteorological information to be supplied.

The service provider shall ensure that the following criteria are part of their QAMS:

Siting

• Proper siting and exposure of instruments
• Establishment and maintenance of station inspection frequency requirements and methods

Validation of instruments

• Instruments shall be tested over a range that is representative of the expected environmental conditions (regardless of whether in a controlled environment or in the field)
• Istruments shall be verified to meet performance requirements, in accordance with requirements set out in the Guide to Meteorological Instruments and Methods of Observation, WMO-No. 8, as amended from time to time, or equivalent developed by the service provider by a person who is either;
• Independent from the manufacturer of the meteorological instruments and from the service provider and has a degree in meteorology or the natural or applied sciences or mathematics from a recognized university and experience in: instrumental references, standards and traceability; methods of statistical analysis and an understanding of the operating principles and use of meteorological instruments; or
• A licensed professional engineer (P. Eng) in Canada.

Reporting

• Meteorological observations and reports comply with prescribed standards, including format and content, as specified in this document
• Meteorological reports reflect conditions existing at the actual time of meteorological observations
• Observations are monitored and audited
• Non-conforming observations are identified and corrective measures are taken
• Consistency in the time and frequency of issuance of reports using approved software and procedures
• Retention requirement of weather observing data is for a minimum of 30 days except accident report shall be retained until the inquiry or investigation is completed

Observing

• Manuals and directives, to provide more detailed instructions and training to the service provider’s personnel and users of the QAMS
• The service provider must establish practices and procedures that ensure that all personnel performing work in support of the meteorological service and system are competent to support aviation weather observations that are accurate and that meet standards
• Development and maintenance of operational procedural manuals and documentation
• The service provider shall document the training and competency procedures and make a copy available to, and upon reasonable notice by, TC.

The quality management system shall be audited in accordance with the requirements of the quality management system, and all audit findings shall be evidenced and properly documented.

2.3 Sensor siting

The following are standards for sensor siting:

1. The service provider shall establish and follow practices, procedures and specifications for the siting, installation, commissioning, operation and maintenance of meteorological systems
2. The service provider shall document the practices, procedures and specifications established and shall provide all of the relevant information to Transport Canada , upon reasonable notice given by Transport Canada
3. Except as otherwise required by the regulations set out in MANOBS, meteorological instruments shall be exposed in accordance with the practices, procedures and specifications established by the World Meteorological Organization in the Guide to Meteorological Instruments and Methods of Observation, WMO-No.8 Part III
4. Where the above requirements cannot be met, the service provider shall document any irregularity in the exposure of the meteorological instruments and shall make all of the relevant information available to Transport Canada, upon a request made by the same, within a reasonable timeframe
5. The service provider shall ensure the installation follows a commissioning protocol and establish proof of performance of newly installed sensors or meteorological systems that are in accordance with methods established by the manufacturer, or equivalent documentation developed by or for the service provider

2.4 Automated weather observing systems

The observation requirements for wind direction, speed and character, temperature, dew-point temperature, or atmospheric pressure as altimeter setting, are instrumental. However, where human observers utilize these weather elements, they shall provide quality monitoring and backup as required.

The standards for Automated Weather Observing Systems (AWOS) and Limited Weather Instrument Systems (LWIS) set out in MANOBS are based on the results of testing and consultation. Thus, many routines of the signal processing algorithms employed by AWOS/LWIS are outlined here as the minimum required processing for METAR AUTO. METAR AUTO is intended specifically for the METAR, SPECI and TAF as a stand-alone automatic dependent system used for aerodrome observations and forecasting. Standards for automated weather observing systems are given in Chapter 12.

2.5 Types of staffed observations

2.5.1 Aerodrome routine meteorological report (METAR)

METAR is the primary observation code reported on the hour (UTC) for surface meteorological data. METAR contains a report of wind, visibility, runway visual range, present weather, sky condition, temperature, dew-point, and altimeter. In addition, coded and/or plain language information elaborating on weather elements can be found in the “Remarks” section.

2.5.2 Aerodrome special meteorological report (SPECI)

SPECI is an unscheduled report taken when any of the selected changes in weather conditions significant to aviation occur off the hour. SPECI shall contain all data elements found in a METAR. In addition, coded and/or plain language information elaborating on weather elements can be found in the “Remarks” section.

2.5.3 Accident observation

The following are standards for accident observations:

1. Immediately upon learning of an aircraft accident at or near the weather observing station, the observer shall make an accident observation
2. The accident observation shall be recorded and transmitted
3. It shall be as complete and accurate as possible, with particular care being taken to include in Remarks the words “Accident Report” and any meteorological facts that might relate to the accident, or might be of significance to the Aircraft Accident Investigator
4. The service provider shall preserve the integrity of accident observations
5. All accident observations shall be retained until the inquiry or investigation is completed

2.6 Point of observation

All METAR and SPECI shall be representative of conditions at or near the aerodrome reference point, as if observed from an out-of-doors location at ground or water level where a minimum of obstacles to the view of the full circle of the horizon and the full celestial dome exist.
Documentation shall be maintained by the aviation weather service provider to show how compliance with the above paragraph is achieved.

2.7 Parameters to be observed during an METAR/SPECI/Accident Observation

The data listed below shall be included in the reported METAR, SPECI and Accident Observation:

• sky condition
• visibility
• weather and obstruction to vision
• sea level pressure
• temperature
• dew-point
• wind
• altimeter setting
• clouds
• remarks
• RVR (if available and reportable)
• tendency1

2.8 Times of observations

The standard time of observation is determined by international agreement; it is referenced to Coordinated Universal Time (UTC) and is published in the WMO Technical Regulations. In the aviation community Zulu time “Z” is often used in lieu of UTC; MANOBS reflects the use of both abbreviations.

The following are standards for times of observations:

1. All dates and times entered in observations shall be with reference to the 24-hour clock, UTC
2. The time of a METAR observation shall be on the hour
3. The time assigned to a SPECI observation shall be the time at which the element necessitating the SPECI was observed refer to chapter 2.9.1
4. The time assigned to an Accident Observation shall be the time when advised of the accident
5. For automated systems where SPECI observations are required, a full observation shall be performed each minute
6. The SPECI observation shall be the minutely observation containing the weather element that has changed according to the standards for issuing SPECI

2.9 Scheduled observations

The barometer shall be read exactly on the hour. Other elements shall be observed in the few minutes preceding the hour and as close as possible to the hour. The computations, coding and recording of METAR observations shall be done immediately after the hour.

The schedule of observations found in Table 2 – 1 applies when only the hourly observation is required.

The schedule of observations found in Table 2 – 2 applies when both hourly and synoptic observations are required:

2.9.1 Time assigned to SPECI observations

A SPECI observation shall be taken and reported whenever one or more of the elements listed in section 11.2.3 have changed in the amount specified (except in the case of end of thunderstorm or precipitation). The amount of change is with reference to the preceding METAR or SPECI observation. If more than one element has changed sufficiently to trigger a SPECI, the time shall be the time of observation of the element considered to be the most important to aviation.

A SPECI should be reported within “Time of SPECI +5 minutes.” This is the time allowed to issue a SPECI without it being considered reported late. This allowed time period is for sites that have more than weather observing as their main responsibility.

2.9.2 Late observation

To ensure that users of weather observations have confidence in the observations and use them safely, hourly observations must be accurate and adhere to the schedules specified in section 2.8. Every effort must be made to ensure that weather observations are taken on time. However, should an occasion arise that is beyond the control of the observer and that necessitates taking the observation late, the following shall apply:

1. the number of minutes after the hour that the observation has been taken shall be entered as the first of the general weather remarks
2. the format of the remark shall be, “OBS TAKEN +tt”, where “+tt” indicates the number of minutes the observation was taken after the hour

Example: The observation was taken 18 minutes after the hour (barometric values and other direct-ingest weather data are from the hour):
METAR CYAM 101300Z 00000KT 15SM FEW012 FEW220 M20/M22 A3039 RMK SC1CI1 OBS TAKEN +18 SLP308

2.9.3 Observation program remarks

To enable users of weather observations to determine if a station is staffed or when the next observation will be, remarks indicating the status of operation are required.

At sites with a 24-hour program and a staff/machine mix for observations, enter the status of operation in the Remarks section for the last staffed observation of the day.

Example: The last daily staffed weather observation is issued at 03Z; the next staffed weather observation will be issued at 13Z:
METAR CYXH 100300Z 28015G21KT 15SM FEW270 03/M02 A3001 RMK CI2 LAST STFD OBS/NEXT 101300Z SLP187

At sites with less than a 24-hour observation program and observations not supplemented by those of an automatic station, enter in the Remarks section for the last observation of the day.

Example: The last daily weather observation is issued at 03Z; the next weather observation will be issued at 13Z:

METAR CYGK 100300Z 20005KT 15SM SCT090 BKN110 21/17 A2994 RMK AC3AC2 LAST OBS/NEXT 101300UTC SLP138

2.10 Duties

The meteorological elements entered in a meteorological report shall, as closely as possible, reflect the conditions existing at the actual time of the meteorological observation. While on duty, weather observers are required to keep a close and continuous watch on the weather. Their records and reports shall be as complete and accurate as possible. If communication or other difficulties delay or prevent the distribution of reports; the observers shall continue to observe the weather and record their observations on schedule. It is essential that climatological records be complete. Whenever an error is detected in a disseminated report, a correction shall be issued as soon as is practical.

Any attempt by any individual to have the observer alter any portion of an observation in such a manner as to decrease its accuracy to suit the purpose of an individual or organization shall be reported by letter immediately, giving full details to:

Director, Standards
Transport Canada
330 Sparks Street
Ottawa, Ontario   K1A 0N8

2.10.1 Priority of duties

Personnel who take weather observations as only one component of their duties shall give such duties the priority specified by their employing agency. Any other personnel whose primary duty is to observe the weather shall maintain a continuous weather watch and shall give the highest priority to weather observing duties.

Chapter 3. Wind standards

3.1 General information

This chapter describes the wind information that is required to be contained in a METAR/SPECI and the standards for the instrument that measured the winds. Standards for wind characteristics such as calm wind, gusts, squalls, wind shift, variable wind direction, variations in wind direction and estimation of wind are given. Tables for estimating wind and examples of surface weather reports are also given.

3.2 General wind standards

3.2.1 Reporting

The following are standards for reporting wind:

1. Wind information is included in all surface weather reports and shall contain both velocity (direction and speed) and character
2. Wind direction shall be reported with respect to true North and the speed shall be expressed in nautical miles per hour (knot, abbreviated as “kt”)
3. The wind direction and speed reported in the METAR/SPECI/Accident Observation shall be a two‑minute mean
4. The direction shall be determined to the nearest ten degrees and the speed to the nearest knot.
5. The occurrence of gusts, squalls, variable wind direction, variations in wind direction and wind shifts shall be reported

3.2.2 Wind instruments

The following are standards for wind instruments:

1. The wind measurements shall be representative of winds that are 10 m above the ground over level terrain at a distance equal to at least 10 times the height of any object from that object or, if this is not possible, at such a height and location that the indications are reasonably unaffected by local obstructions
2. The wind velocity is averaged over a two-minute period and the wind speed is reported in knots
3. The instruments shall function for winds of up to and including at least 100 kt speed

3.2.3 Wind direction

The wind direction is the direction from which the air is moving. It represents the average direction during the two-minute period ending at the time of observation.

The following are standards for wind direction:

1. Wind direction shall always be reported using three digits, in degrees true, and rounded off to the nearest 10 degrees
2. Values of wind direction less than 100 degrees shall be preceded by a zero
3. Wind from true north shall be encoded as 360
4. Wind direction for calm winds shall be encoded as 000

3.2.4 Calm wind

The following are standards for calm wind:

1. Calm wind may be reported for mean wind speeds less than 2 kt
2. Calm wind of 1 kt or less shall be reported as calm wind
3. Calm wind shall be coded as 00000 followed immediately, without a space, by KT to specify the units

3.2.5 Wind speed

The wind speed is the rate of airflow past a fixed point. It represents the average speed during the two-minute period ending at the time of observation.

The following are standards for wind speed:

1. Wind speed shall be reported using two digits if under 100 kt, or by using three digits if 100 kt and over
2. Wind speed of 00 and 01 kt shall be encoded as 00KT

3.3 Reporting standards for wind characteristics

3.3.1 Gusts

Gusts are sudden, rapid and brief changes in the wind speed. They are characterized by more or less continual fluctuations between high (peak) and low (lull) speed.

The following are standards for gusts:

1. The speed of a gust shall be the maximum wind speed, in kt, averaged over a maximum of a five-second period
2. Gusts shall be reported when both of the following criteria are met:
   1. the highest peak speed is at least 5 kt higher than the current two-minute average
   2. the highest peak is at least 15 kt

3.3.2 Squalls (SQ)

The following are standards for squalls:

1. Squall shall be reported when all of the following occur:
   1. the wind speed increases by 15 kt or more over the two-minute average speed that preceded the increase
   2. the duration of the peak speed period is at least 2 minutes
   3. the wind speed attains a one-minute mean of at least 20 kt, during the peak speed period
   4. the wind speed diminishes by at least 5 kt
2. The speed to be reported shall be the highest one-minute mean speed during the squall period
3. When squalls are observed, the peak wind speed shall be reported as a gust and SQ shall be reported in present weather

3.3.3 Wind shift

Wind shift is a definite change in the general direction from which the wind is blowing.

The following are standards for wind shift:

1. A wind shift shall be recorded when all of the following occur:
   1. the direction from which the wind is blowing changes by 45° or more
   2. the change in direction takes place in less than 15 minutes
   3. the direction at the completion of the shift shall not be variable
   4. the average wind speed at the completion of the shift is 10 kt or more
2. The time of the wind shift shall be the time at which the wind begins to shift
3. The time of a wind shift shall be recorded in Remarks

3.3.4 Variable wind direction

In the case of variable wind direction, the wind direction shall be coded as VRB when the wind speed is less than 3 kt. A variable wind at higher speeds shall be reported only when the variation of wind direction is 180° or more, or when it is impossible to determine a single wind direction.

3.3.5 Variations in wind direction

If, during the 10-minute period preceding the observation, the total variation in wind direction is 60° or more and less than 180°, and the mean wind speed is 3 kt or greater, the observed two extreme directions between which the wind has varied shall be reported in clockwise order.
Example: 240V350

3.3.6 Estimation of wind

The following are standards for the estimation of wind:

1. When suitable instruments are lacking or when the instruments are not in operating condition, the wind direction (to eight points of the compass), the wind speed and character shall be estimated
2. The observer shall not estimate the peak speed of a gust or squall
3. If winds are estimated, the following remark shall be included in the report: WIND EST

3.3.6.1 Estimates of wind speed by Beaufort scale of winds

When the observer lacks any other method to determine wind speed, the wind speed shall be estimated using the Beaufort scale of winds. This scale relates the equivalent speeds in knots of common effects of wind. Report the Beaufort scale knots average for the speed.

3.4 Examples of wind remarks

Example: The wind direction and speed at 1645Z was 20025KT, then the wind direction started to shift at 1650Z and at 17Z the wind direction and speed was 27040G55KT:
METAR…27040G55KT …RMK… WSHFT 1650

If winds are estimated, the remark WIND EST shall be included in the report:
METAR…14014KT …RMK… WIND EST

Chapter 4. Visibility standards

4.1 General information

This chapter defines visibility and describes the standards for reporting visibility, including the standards related to the unit of measure, variable visibility and identification of the elevated position. Descriptions of prevailing visibility, point of observation and visibility charts are given. Examples of visibility remarks are also provided.

4.1.1 Definition of visibility

Visibility, for aeronautical purposes, is defined as the greater of:

1. the greatest distance at which a black object easily recognized, situated near the ground, can be seen and recognized when observed against a bright background; or
2. the greatest distance at which lights in the vicinity of 1 000 candelas can be seen and identified against an unlit background

4.2 Prevailing visibility

It is the maximum visibility value common to sectors comprising one-half or more of the horizon circle. Prevailing visibility is reported in international statute miles and fractions up to 3 mi., then in whole miles up to 15 mi., and in units of 5 mi. thereafter, where suitable visibility markers are available.

The visibility to be reported is the prevailing visibility observed at eye level (internationally defined as 1.5 meters above the ground).

4.3 Point of observation

Prevailing visibility is determined at the surface. A roof is convenient for enabling the observer to obtain a complete view of the horizon circle. However, if the observer has any reason to believe that the visibility near the ground is different, the observer shall make an observation from the ground and record it as the prevailing visibility.

Optical devices used to enhance visibility, such as binoculars, shall not be used by the observer when determining visibility.

Recorded visibility shall not be reduced on account of darkness alone.

4.4 Visibility charts

Visibility charts shall be available for each observing station and shall include day and night markers that are valid for use in all four seasons.

Visibility charts shall be reviewed on a continuous basis and updated as required.

4.5 Visibility observing standards

4.5.1 Units of measure

Visibility shall be reported at land stations in international statute miles (SM).

4.5.1.1 Visibility between two reportable values

If the observed value of visibility is between two reportable values, then the lower value shall be reported.

4.5.1.2 Maximum reportable value

If suitable markers beyond 15 mi. are lacking, then 15 mi. is the maximum reportable value.

4.5.1.3 Sector visibility

If the visibility in one or more directions is half or less, or double or more, of the prevailing visibility, details of the visibility in such directions shall be reported in Remarks.

4.5.2 Variable visibility

If the prevailing visibility is observed to be fluctuating rapidly and increasing and decreasing from a mean value by ¼ or more of the mean value, the range of variation shall be entered in Remarks beginning with the lowest visibility value. The mean value shall be entered as the prevailing visibility.

4.5.3 Elevated positions

When observing visibility from elevated positions, such as a control tower or roof, if the visibility differs by a reportable value from the prevailing visibility observed on the ground (at eye level), the visibility from the elevated position and the identification of that position shall be reported in Remarks. The observer shall provide an estimate of the depth of the fog as well as the roof-top visibility.

4.6 Examples of visibility remarks

METAR...1/2SM FG ...RMK... VIS VRB 1/4-3/4
METAR...10SM PRFG ...RMK... FG BANK VIS W 2
METAR...3/4SM BR ...RMK... VIS IMPR RPDLY
METAR...1/2SM BLSN ...RMK... TOWER VIS 2
METAR... 0SM FG ...RMK... VIS 100 FT
METAR...3/4SM BR ...RMK... FG DSIPTG RPDLY
METAR...1/4SM FG ...RMK... FG 45 FT THK ROOF VIS 2
METAR...10SM ...RMK... FU DRFT OVR FLD VIS N 1
METAR...6SM -RA BR ...RMK... BCFG VIS SE 1/4
METAR...1/2SM FG ...RMK... PRFG SE-N
METAR...10SM BCFG ...RMK... VIS SE QUAD 1/2

Chapter 5. Runway visual range (RVR)

5.1 General information

This chapter details standards for reporting RVR and provides examples of RVR remarks used in surface weather reports.

5.1.1 Definition of runway visual range

Runway visual range (RVR) is the range over which the pilot of an aircraft, located on the centre line of a runway, can see the runway surface marking or the lights delineating the runway or identifying its centre line. RVR is used for determining the landing and take-off conditions for aircraft pilots. RVR observations should be representative of the touchdown zone. RVR is used as one of the main criteria for minima on instrument approaches, as in most cases a pilot must obtain visual reference of the runway in order to land an aircraft.

5.2 Standards for reporting

The assessment of runway visual range output shall be updated at least every 60 seconds to permit the provision of current representative values. The averaging period for runway visual range values shall be 10 minutes for METAR and SPECI, except when the 10-minute period immediately preceding the observation includes a marked discontinuity in runway visual range values. If this is the case, only those values occurring after the discontinuity shall be used to obtain mean values.

Runway visual range inclusion in the METAR or SPECI is generally automated and is only included when at least one RVR reports 6 000 ft or less, or reported prevailing visibility is 1 mi. or less.

The maximum RVR reportable range is “6 000 ft plus,” encoded as P6000. The minimum RVR reportable range is 300 ft, encoded as M300.

The following shall apply to reports of runway visual range:

1. Runway visual range shall be reported in:
   1. increments of 100 ft from the minimum reportable value of the RVR detection equipment up to 1 200 ft
   2. increments of 200 ft from 1 200 ft to 3 000 ft
   3. increments of 500 ft from 3 000 ft to 6 000 ft or the maximum reportable value for the RVR detection equipment whichever is less
2. If the assessed value is between the reportable values in accordance with paragraph 1), then the reported value of runway visual range shall be lowered downward to the next lower reportable value
3. In reports of runway visual range intended for take-off or landing, the most recent one-minute-mean value shall be used

5.2.1 Requirements for the assessment of runway visual range based on instrumented systems

1. The installation, siting, exposure, operation and maintenance of the system shall be such that:
   1. instruments used for the assessment of runway visual range shall be located within 120 m of the centerline of the runway
   2. the height of the optical path is between 2.5 m and 5 m above the level surface of the runway
   3. a background luminance detection sensor shall be used that is accurate to within 10% with at least a 90% confidence
   4. the extinction coefficient assessment is within:
      1. 20% of the root mean square value of a reference transmissometer, with at least a 90% confidence, for measured values from 0.001/m to 0.01/m
      2. 15% of the root mean square value of a reference transmissometer from 0.01/m to 0.105/m
2. Sensors used to assess the extinction coefficient or scatter coefficient as part of the calculation of the runway visual range:
   1. are traceable to a transmissometer standard
   2. have documented performance characteristics with respect to the full range of hydrometeors that can be expected at the aerodrome
   3. provide either no report, or a report of a very low runway visual range, in the event of instrumental failure or blockage of the sampling volume
3. There are displays relating to each runway visual range sensor that are:
   1. clearly marked to identify the runway and the section of the runway to which they correspond
   2. reporting values of runway visual range that are updated at least every 60 seconds and are available within 15 seconds of the end of the averaging period
4. The runway light intensity to be used for calculation of runway visual range, for use in METAR/SPECI, shall be the maximum light intensity
5. The runway light intensity to be used for calculation of runway visual range for operational flight information shall be:
   1. if the runway lights are switched on, the actual runway light intensity in use on that runway
   2. if the runway lights are switched off, the minimum intensity runway light intensity
   3. degraded to account for aging and contamination of the lamps

5.2.2 Significant Variation

When the RVR at a runway varies significantly and when, during the ten-minute period preceding the normal observation time, the one-minute-mean extreme values assessed vary by more than 150 feet, or more than 20% of the mean value, whichever is greater, the one-minute-mean minimum and the one- minute-mean maximum values shall be recorded instead of the ten-minute mean. Tendency shall also be indicated.

5.2.3 Tendency

If the runway visual range values during the ten minute period preceding the observation show a distinct upward or downward tendency such that the mean during the first five minutes varies by 300 feet or more from the mean during the second five-minute period, a tendency shall be indicated as either upward or downward.  When no distinct change in runway visual range is observed, the tendency shall indicate that no distinct change has been observed.  When it is not possible to determine the tendency, tendency shall be omitted.

5.3 RVR Remarks

Runway visual range remarks are automatically generated by an RVR system. Use RVR MISG when RVR data is not available.

The only time RVR remarks are included in the METAR or SPECI by the observer is when the RVR system has lost communication with the weather system. For manual reports of RVR, the most recent one‑minute-mean value may be used in the remarks of the METAR or SPECI for the RVR intended for take-off or landing. The following is an example of manually entered RVR remarks:
RVR RWY 15 3500FT

Chapter 6. Atmospheric phenomena standards

6.1 General information

This chapter defines present weather and describes the standards for reporting atmospheric phenomena, determining intensity and character, and for observing miscellaneous phenomena and unusual weather conditions. This chapter is structured to provide a definition, standards for reporting, and examples of remarks for each of the following present weather phenomena: tornadoes, waterspouts, funnel clouds, thunderstorms, lightning, precipitation, and obstructions to vision.

6.2 Present weather

6.2.1 Definition

Present weather is defined as weather that is occurring at the time of observation, which includes all atmospheric phenomena observed, with the exception of clouds. This includes forms of precipitation as well as weather phenomena that obstruct vision.

6.2.2 Standards for reporting

The observation and reporting of present weather by human observers shall be inclusive of the weather phenomena (as detailed in sections 6.3 through 6.7) that are occurring at and/or are visible from the aerodrome.

Observed present weather phenomena shall be reported in terms of type and characteristics, and qualified with respect to intensity or proximity to the aerodrome, as appropriate.

6.3 Tornadoes (+FC), Waterspouts (+FC), and Funnel Clouds (FC)

6.3.1 Definition

Tornadoes: A rotating column of air, extending from the base of a cumuliform cloud (usually Cumulonimbus), and often visible as a condensation funnel in contact with the ground, and/or attendant circulating dust or debris cloud at the ground.

Waterspouts: A tornado occurring over water. It is normally a relatively small, weak rotating column of air over open water below a Cumulonimbus or Cumulus congestus (towering Cumulus) cloud.

Funnel clouds or cold-air funnels: A funnel cloud, or (rarely) a small relatively weak tornado, that can develop from a small shower or thunderstorm when the air aloft is unusually cold. Cold-air funnels typically do not reach the ground (funnel cloud), but when they do reach the ground as tornadoes, they are much less violent than the other types.

6.3.2 Standards for reporting

1. Tornadoes, funnel clouds and waterspouts shall be reported as occurring “at the station” when within sight (at any distance)
2. The code +FC shall be used to report any tornado (when it occurs over land) or waterspout (when it occurs over water) that is within sight
3. The code FC shall be used to report any funnel cloud when within sight
4. A tornado or waterspout shall not be reported when the vortex does not reach the ground, or when the observer is not sure that the vortex of the funnel reaches the ground (or water), that is, a “bush” is not observed
   1. in this case, “funnel cloud” (FC) and its direction from the station shall be reported
   2. The observer shall note the direction of the storm from the station and the direction in which it is moving
   3. The plain language words TORNADO or WATERSPOUT shall be inserted in the Remarks whenever these phenomena are observed

   6.3.2.1 Intensity

   Intensity values are not ascribed to tornadoes or waterspouts.

   6.4 Thunderstorm (TS)

   6.4.1 Definition

   A thunderstorm is a local storm that is produced by a Cumulonimbus cloud, and is always accompanied by lightning and thunder, usually with strong gusts of wind, heavy rain, and sometimes with hail. Lightning may not be always visible to the naked eye.

   6.4.2 Standards for reporting

   Thunderstorm activity at the station shall be reported when:

   1. thunder is first heard
   2. overhead lightning is observed and the local noise level might prevent the observer from hearing thunder (in this case, hail may also be an indicator of a thunderstorm in progress)

   6.4.2.1 Time of beginning of thunderstorm

   The time of beginning of a thunderstorm shall be recorded as the time of the earliest occurrence that indicates thunderstorm activity at the station.

   6.4.2.2 Time of ending of thunderstorm

   When thunderstorm activity at the station has not occurred in the last 15 minutes, the observer shall record the thunderstorm as having ended 15 minutes before.

   6.4.2.3 Intensity

   No intensity is ascribed to thunderstorms.

   6.4.3 Examples of thunderstorm remarks

   METAR...BKN045CB 10SM TS ...RMK... CB W MOV N
   SPECI...BKN025CB 7SM –TSRA ...RMK... CB OHD MOV SE

   6.5 Lightning

   6.5.1 Definition

   A luminous manifestation accompanying a sudden electrical discharge that takes place from or inside a cloud or, less often, from high structures on the ground or from mountains. Three main types of lightning can be distinguished: cloud-to-ground, intra-cloud, and cloud-to-cloud. In addition, there are other forms of luminous electrical manifestations.

6.5.2 Standards for reporting

When lightning is observed, the following shall be reported:

1. frequency, reported as OCNL (occasional), FRQ (frequent), CONS (continuous)
2. type, reported as LTGCG (Lightning Cloud-to-Ground), LTGIC (Lightning Intra-Cloud), and LTGCC (Lightning Cloud-to-Cloud)
3. direction from station

The following may be used as a guide for the frequency of lightning:

• OCNL less than one flash per minute
• FRQ one to six flashes per minute
• CONS more than six flashes per minute

6.5.3 Examples of lightning remarks

When only one lightning type is visible, the remark is of the form:
METAR...SCT035CB 10SM ...RMK... LTGIC SW

When multiple lightning types are visible, the remark is of the form:
SPECI...BKN020CB 7SM TS ...RMK... FRQ LTGCGICCC NW

6.6 Precipitation

6.6.1 Definition

Any product of the condensation of atmospheric water vapour that is deposited on the earth’s surface is a type of precipitation. The types of precipitation that originate aloft are classified in the following sections under liquid precipitation, freezing precipitation, and frozen precipitation.

6.6.1.1 Character of precipitation

Under the term “character,” precipitation is classified as showery, continuous or intermittent.

6.6.1.1.1 Showery precipitation

Showery precipitation falls from cumuliform cloud. Showers often (but not always) begin and end abruptly. Showers usually occur in periods of short duration, perhaps 15 minutes or so, but they may last much longer. Usually there are rapid fluctuations in the intensity of the precipitation. Certain types of precipitation, such as snow pellets and hail, are always showery. The terms “rain showers,” “snow showers” are used to indicate showery character.

6.6.1.1.2 Continuous precipitation

Precipitation that is not showery is considered to be continuous when either of the following criteria apply:

• it continues without a break for at least one hour preceding the time of observation
• it continues without a break since beginning in the hour preceding the time of observation

6.6.1.1.3 Intermittent precipitation

Precipitation that is not showery is considered to be intermittent, when it has stopped and recommenced at least once during the hour preceding the actual time of observation.

6.6.2 Standards for reporting

6.6.2.1 Intermittent and showery precipitation

Precipitation of an intermittent or showery character, which has been active at the station within the preceding 15 minutes, is not occurring at the time of observation, but is expected to begin again soon, shall be reported in Remarks.

6.6.2.1.1 Examples of intermittent precipitation remarks

Example remark for when intermittent precipitation is occurring at the time of observation:
METAR...SCT045 10SM -RA...RMK... -RA INTMT

Example remark for when intermittent precipitation has been active within the preceding 15 minutes, is not occurring at the time of observation, but is expected to recommence:
METAR...OVC040 8SM ...RMK... INTMT –RA

Example remark for when showery precipitation has been active within the preceding 15 minutes, is not occurring at the time of observation, but is expected to recommence:
METAR...BKN025 10SM ...RMK... OCNL -SHRA

6.6.2.2 Liquid precipitation

Liquid precipitation and freezing precipitation shall not be reported in the same observation (by definition one excludes the other).

6.6.2.3 Freezing precipitation

Freezing precipitation shall always appear alone as a separate group.

6.6.2.3.1 Freezing drizzle (FZDZ)

Freezing drizzle shall be reported when the temperature is below zero degrees Celsius or when drizzle is freezing on the ice accretion indicator or on other objects at or near the earth’s surface.

6.6.2.3.2 Freezing rain (FZRA)

Freezing rain shall be reported when the temperature is below zero degrees Celsius or when rain is freezing on the ice accretion indicator or on other objects at or near the earth’s surface.

6.6.2.4 Ice accretion indicator

The horizontal surface of the ice accretion indicator shall be examined, and if ice has formed on it, freezing precipitation shall be reported. If frost has formed on the indicator, or if ice is detected during fog conditions, appropriate remarks for “frost on indicator,” “rime icing on indicator,” etc., shall be recorded and reported.

6.6.2.5 Intensity of precipitation

The precipitations classified as liquid, freezing and frozen (with the exception of ice crystals) are always qualified as to intensity: light, moderate or heavy. The term “light” also includes scattered drops, flakes, grains, pellets or stones accruing at a rate that would not wet or cover a surface, regardless of the duration. The intensities “light,” “moderate,” and “heavy” are determined by considering either the effect on visibility or the rate of fall.

6.6.2.5.1 Intensity of precipitation with an obstruction to vision

The following are standards for reporting the intensity of precipitation with an obstruction to vision:

1. Drizzle occurring with fog shall not be reported as moderate or heavy when the visibility is ⅝ mi. or more
2. Snow with blowing snow shall not be reported as heavy when the visibility is ⅜ mi. or more
3. If multiple precipitation types are observed, the intensity assigned to the group will be that of the predominant precipitation type as determined by the greater intensity
   1. the predominant precipitation shall be reported first in the combined report
4. Freezing precipitation shall be reported as a separate group
5. Intensity shall not be applied to precipitation associated with the proximity qualifier “VC”

6.6.2.5.2 Intensity by rate of fall criteria

Intensity for the following conditions: rain, rain showers, and freezing rain shall be defined using the following criteria:

• Light: if rate of fall is 2.5 mm/h or less
• Moderate: if rate of fall is 2.6 to 7.5 mm/h
• Heavy: if rate of fall is 7.6 mm/h or more

6.6.2.5.3 Intensity by visibility

Visibility for snow, snow showers, snow grains, snow pellets, drizzle, and freezing drizzle shall be defined using the following criteria:

• Light: if visibility is ⅝ mi. or more
• Moderate: if alone¹ and visibility is reduced to ½ or ⅜ mi.
• Heavy: if alone¹ and visibility is reduced to ¼, ⅛, or 0 mi.

6.6.2.6 Rainfall remark

The /Rrr/ group shall be recorded within Remarks and reported only at the hours when the rainfall that has accumulated since the time of the last main synoptic report equals or exceeds 10 mm (rounded), or exceeds the previously reported value by 10 mm (rounded) or more.

The letter "R" identifies the precipitation as rain and the letters "rr" the units in whole millimetres.

6.6.2.7 Hail (GR)

Precipitation composed of small balls or pieces of ice (hailstones) with a diameter ranging from 5 mm to 50 mm (sometimes even larger) and which fall either separately or fused into irregular lumps shall be reported using the abbreviation GR.

6.6.2.7.1 Small hailstones (SHGS)

Small hailstones meet the criteria for hail, except that the diameter of the largest stones is smaller than 5 mm. Small hailstones shall be abbreviated as SHGS. Unlike ice pellets, small hailstones may be irregular in shape; it is composed of alternating or concentric layers of transparent and translucent ice.

6.6.2.7.2 Examples of hail remarks

METAR...BKN025CB 4SM TSRAGR ...RMK... HAIL DIAM 12 MM
METAR...BKN025CB 4SM TSRAGS ...RMK... HAIL DIAM 04 MM

6.6.2.8 Ice Crystals (IC)

When ice crystals (IC) are observed, this observation shall be reported in the METAR or SPECI with any reportable visibility.

6.6.2.9 Snowfall

The /Sss/ group shall be recorded and transmitted only at the hours when the snowfall that has accumulated since the time of the last main synoptic report equals or exceeds 1 cm (rounded), or exceeds the previously reported value by 1 cm (rounded) or more. The letter S identifies the precipitation as snow and the letters ss identify the units in whole centimetres. If all the snow melts as it hits the ground, /Sss/ would not be reported.

6.7 Obstructions to vision

6.7.1 Standards for reporting obstructions to vision

Obstructions to vision shall be recorded only when the prevailing visibility is 6 mi. or less.

6.7.2 Fog (FG)

Fog shall only be reported when the prevailing visibility is reduced to ½ mi. or less at the earth’s surface.

6.7.2.1 Freezing Fog (FZFG)

Freezing fog shall be reported when the temperature is in the range of -0.1 to -30.0 °C and the visibility is ½ mi. or less. When temperatures are colder than -30.0 °C and visibility is ½ mi. or less, freezing fog shall be reported if there is clear physical evidence of ice accretion from fog.

6.7.3 Mist (BR)

Mist shall be reported when the prevailing visibility is reduced to a range of ⅝ to 6 mi., inclusive.

6.7.4 Fog Patches (BCFG)

Fog patches consist of fog extending to at least 1.5 m. above ground level with a coverage of less than 50% of the ground normally visible from the observing point. The letter abbreviation BCFG shall be used to report fog patches covering part of the aerodrome. The apparent visibility in the fog patch shall be ½ mi. or less. BCFG should be used only when the visibility in parts of the aerodrome is more than ½ mi. However, when the fog is close to the point of observation, the minimum visibility will be ½ mi. or less (see Appendix 2).

6.7.4.1 Example of BCFG Remarks

METAR...6SM -RA BR ...RMK... BCFG SE VIS 1/4

6.7.5 Fog covering part of aerodrome (PRFG)

Fog covering part of aerodrome describes a fog bank or area of fog (or freezing fog) which may have small breaks; however, within the area of fog at least 50% of the ground must be covered (see Appendix 2). Non-patchy fog (more or less continuous fog) extends to at least 1.5 metres above ground level, covering part of the aerodrome. The apparent visibility within the area of fog shall be ½ mi. or less (see Appendix 2).

6.7.5.1 Example of PRFG remarks

METAR...2SM BR ...RMK... PRFG SE-N

6.7.6 Shallow Fog (MIFG)

Low-lying fog that does not obstruct the visibility at eye level (1.5 metres above the surface), even if the visibility within the fog is ½ mi. or less (see Appendix 2). Low-lying fog usually occurs with a clear sky or high thin cloud conditions.

6.7.6.1 Example of MIFG Remark

METAR...10SM MIFG ...RMK... MIFG OVR APCH RWY 27

6.7.7 Blowing snow (BLSN), blowing dust (BLDU), blowing sand (BLSA)

Blowing snow, blowing dust, blowing sand shall be reported when prevailing visibility is 6 mi. or less and it is the only factor reducing visibility.

6.7.8 Dust storm (DS), and sandstorm (SS)

Dust storms, and sandstorms shall be reported when the prevailing visibility is 6 mi. or less and it is the only factor reducing visibility, and shall be reported as heavy when the prevailing visibility is reduced to ¼ mi. or less.  

6.7.9 Haze (HZ), dust haze (DU), smoke (FU)

Haze, dust haze, and smoke shall be reported when the prevailing visibility is reduced to 6 mi. or less.

6.7.10 Volcanic Ash (VA)

Volcanic ash shall be reported regardless of the prevailing visibility.

6.7.11 Vicinity (VC)

The vicinity qualifier VC shall be used when specific weather phenomena are observed within 5 mi. or less, but are not occurring at the point of observation.

The vicinity qualifier VC shall be used with the following weather phenomena: VCSH (showers), VCFG (fog), VCBLSN (blowing snow), VCBLDU (blowing dust), VCBLSA (blowing sand), VCPO (dust/sand whirls), VCDS (dust storm), VCSS (sandstorm), VCVA (volcanic ash).

6.8 Visibility reduced below eye level

Visibility is reduced below eye level whenever a meteor, other than precipitation, has veiled or hidden very low objects, but the visibility at eye level is not appreciably restricted.

6.8.1 Drifting dust (DRDU), drifting sand (DRSA) and drifting snow (DRSN)

Drifting snow, sand or dust shall not be reported in the same observation as blowing conditions of the same phenomenon; by definition, one excludes the other. For example drifting snow shall not be reported with blowing snow.

Chapter 7. Sky condition standards

7.1 General information

This chapter describes the standards for reporting sky conditions and the definition of cloud types. Terms and definitions are given for celestial dome, sky condition, obscuring layers, total amount, and reference level. Sky condition standards are given for cloud amount, vertical visibility, and variable ceiling, followed by examples of remarks. Abbreviations of cloud types and obscuring phenomena for use in reporting sky conditions are also provided.

7.2. Terms and definitions

7.2.1 Celestial dome

In this chapter, “celestial dome” refers to that portion of the sky that would be visible if there was an unobstructed view of the horizon in all directions from the point of observation.

7.2.2 Sky condition

An observation of the sky requires an examination and identification of the clouds and obscuring phenomena (fog, smoke, precipitation, etc.) which prevent an uninterrupted view of the sun, moon, stars or the clear blue of the celestial dome. Such obstructions occur as layers aloft with comparatively level bases or as surface-based layers. Each layer is analyzed for its type, amount, and height of base, or vertical visibility.

7.2.3 Obscuring layers

An “obscuring layer” is a non-cloud layer which either wholly or partly prevents an observer from seeing the sky or clouds at higher levels.

7.2.4 Transparent layers

A layer aloft that does not conceal a layer or portion of a layer above.

7.2.5 Total amount

Total amount is the amount in oktas, of the whole sky that is covered by all layers observed.

7.2.6 Summation amount

The sum of individual layer amounts in oktas. However, traces of layers, aloft or surface-based, shall be disregarded when determining summation amount.

7.2.7 Ceiling

Ceiling is the lowest layer aloft reported as broken (BKN) or overcast (OVC) or the vertical visibility (VV).

7.3 Observing and reporting sky condition standards

1. Cloud amount and height of base shall be reported for each cloud layer or, if the sky is obscured, the observed vertical visibility shall be reported
2. The reference point for the observation of sky condition shall be a point from which a minimum of obstructions1 exist to the view of the full celestial dome
3. The reported amount for each observed layer shall be the summation amount covered by all layers at and below that level, excluding ground-based layers
4. Portions of upper layers seen through transparencies in lower layers do not increase the amount of sky cover and shall not be counted when determining the summation amount
5. When observed, CB and TCU of any amount shall always be reported in the remark of the METAR/SPECI
6. When either CB or TCU are the predominant cloud type in a layer reported in the cloud group of the METAR / SPECI then the applicable cloud type (CB or TCU shall be included within the cloud group
7. When an individual layer of cloud is composed of CB and TCU with a common cloud base, the type shall be reported as CB only
8. If the observed cloud amount is between two reportable values, then the lower value shall be reported
9. If there are no cloud bases, the abbreviation SKC (sky clear) shall be reported alone
10. When the sky is obscured, vertical visibility shall be observed and reported, where measured, in lieu of cloud amount, cloud type and height of cloud base
11. The values of cloud bases or vertical visibilities into an obscuring layer shall be reported in increments of 100 ft up to and including 10 000 ft, and in increments of 1 000 ft above 10 000 ft

7.3.1 Reference level

At airport locations, height shall be determined with reference to the official aerodrome level. At non-airport locations, it shall be determined with reference to ground level at the observing station. Table 7 – 1 shall be used as a guide to determine the approximate height of the base of a cloud type.

7.3.2 Cloud amount

7.3.3 Vertical visibility

Vertical visibility shall be reported when the sky is obscured and constitutes a ceiling. Vertical visibility shall be reported to the nearest:

• 100 ft from the surface up to 10 000 ft
• 1 000 ft above 10 000 ft

7.3.4 Variable ceiling

When the ceiling is 3 000 ft or less and is observed to be “variable” (i.e., rising and falling from the mean value by ¼ or more of the mean value), the range of variation shall be indicated in Remarks as:
METAR...OVC003 ...CIG VRB 002-004

7.3.5 Examples of sky condition remarks

METAR...BKN070 ...RMK... AC EXTD RPDLY FM SW
METAR...OVC007 ...RMK... OVC TPG HILLS NE
METAR...FEW250 ...RMK... CONTRAILS¹

7.4 Abbreviations of cloud types and obscuring phenomena

Chapter 8. Air and dew-point temperature

8.1 General information

This chapter provides definitions of terms and describes the standards for air and dew-point temperature.

The temperature of a body is the condition which determines its ability to communicate heat to other bodies or to receive heat from them. In a system of two bodies, the one that loses heat to the other is said to be at the higher temperature. With the latest technologies, the temperature is now derived from automated instruments which already have corrections and tolerances built into them.

8.2 Terms and definitions

8.2.1 Temperature

Temperature is a measure of the warmth or coldness of an object or substance with reference to a standard value. It is measured in degrees Celsius (C).

8.2.2 Humidity

Humidity is a measure of the water vapour content of the air. It is calculated with respect to water, both at temperatures above and below freezing. Humidity is commonly expressed in terms of dew-point temperature and relative humidity.

8.2.3 Dew-point

The dew-point is the temperature at which the air would become saturated (with respect to water) if cooled at constant pressure and without the addition or removal of water vapour. The dew-point is expressed in degrees Celsius.

8.2.4 Relative humidity

Relative humidity is the ratio, expressed as a percentage, of the amount of water vapour actually present in the air to the amount of water vapour which would be present if the air were saturated with respect to water at the same temperature and pressure.

8.3 Temperature standards

The following are standards for reporting air temperature and dew-point:

1. The air temperature and dew-point temperature shall be rounded to the nearest whole degree Celsius
2. Observed values involving 0.5 °C shall be rounded up to the next highest (warmer) degree Celsius
3. Rounded whole-degree single-digit values (-9 °C to +9 °C) of air temperature and dew-point temperature shall be preceded by 0 (e.g., M09 or 09)
4. Temperatures below 0 °C shall be immediately preceded by M to indicate the temperature is minus

8.3.1 Examples of reports of temperature in METAR

METAR...06/M00...

Chapter 9. Atmospheric pressure standards

9.1 General information

This chapter first defines station elevation and the units of measurements used for atmospheric pressure, and then the standards for observing and reporting atmospheric pressure are described.

9.1.1 Atmospheric pressure

Atmospheric pressure, also called barometric pressure, is the force per unit area exerted by the atmosphere as a consequence of its weight, and thus is equal to the weight of a vertical column of air of unit area, extending from the level in question to the outer limit of the atmosphere.

A barometer for aviation purposes shall contain two or more independently operating sensors each of which is traceable to a WMO primary standard barometer.

9.1.2 Station elevation

The station elevation is the vertical distance in metres above Mean Sea Level (MSL) of the datum level to which barometer readings are corrected to give station pressure.

At surface weather observing sites located at airports, the station elevation is equal to the aerodrome elevation as reported in the Canada Flight Supplement.

At non-airport located surface weather observing sites, the station elevation is equal to the elevation of the electronic barometer.

9.1.3 Units of measurement

The unit of measurement of atmospheric pressure is hectopascals; the corresponding symbol is hPa.

9.2 Pressure standards

Meteorological observations of atmospheric pressure intended to be provided as meteorological reports of altimeter setting shall meet the following requirements:

1. The atmospheric pressure for aviation purposes shall be measured using a digital barometer containing two or more independently operating sensors meeting the requirements of section 12.2.6
2. The sensors shall be installed and operated in accordance with the manufacturer’s specifications, or equivalent specifications developed by the service provider
3. The sensors shall be accurate to within 0.02 inches of mercury
4. The altimeter setting (QNH) value shall be rounded down to the nearest whole hundredths of inches of mercury using four digits preceded, without a space, by the letter indicator “A”
5. The computed sea level pressure shall be reported in observations so that the barometric pressures at stations of different elevations can be compared at a common level for synoptic purposes
6. Altimeters shall have quality control that in the event of sensor failure prevent the report from being issued

9.2.1 Mandatory remarks

The remark PRESRR is used when the pressure trace indicates that the station pressure is rising at the rate of 2.0 hPa per hour or more at the time of observation.

The remark PRESFR is used when the pressure trace indicates that the station pressure is falling at the rate of 2.0 hPa per hour or more at the time of observation.

9.2.2 Sea level pressure (SLPppp)

SLP: Group indicator that precedes the sea level pressure.
ppp: Sea level pressure in hectopascals. The recorded values are the last three digits including the tenths of the measured pressure.

Chapter 10. General aviation remarks

10.1 General information

This chapter explains what general aviation remarks are and outlines the standards for their usage. Criteria for inclusion of remarks and supplementary meteorological information are also provided.

10.2 Standards for the inclusion of remarks

The following are standards for the inclusion of remarks in meteorological reports:

1. The indicator RMK denotes the beginning of a section containing information included by national decision
2. General aviation remarks, defined as meteorological information of importance to aviation and other users not captured elsewhere in the METAR/SPECI, shall be recorded under Remarks
3. The observer shall use discretion in the understanding that the METARS are disseminated globally
4. Standard abbreviations from the Manual of Word Abbreviations (MANAB) shall be used (plain language may also be used, provided all terms are spelled out fully and well understood by users)
5. All reports from human sites shall contain remarks and supplementary meteorological information, which at a minimum shall include each of the following, when present:
   • cloud layer type, amount, and obscuring phenomena
   • TORNADO, FUNNEL CLOUD or WATERSPOUT shall be spelled out in the Remarks section
   • lightning as per 6.5.3
   • volcanic eruption or volcanic ash as per 6.7.10
   • wind as per 3.4
   • visibility as per 4.6
   • sky condition as per 7.3.5
   • significant pressure changes as per 9.2.1
   • character of precipitation as per 6.6.2.1.1
   • snowfall amount as per 6.6.2.9
   • rainfall amount as per 6.6.2.6
   • hail size as per 6.6.2.7.2
   • RVR as per 5.3
   • late weather observations as per 2.9.2
   • observation program status as per 2.9.3
   • SLPppp

Chapter 11. METAR—Aerodrome routine meteorological report

11.1 General information

METAR (Aerodrome routine meteorological report) is the primary observation code reported on the hour (UTC) when reporting surface meteorological data. SPECI (Aerodrome special meteorological report) is an unscheduled report taken when any of the selected changes in weather conditions significant to aviation occur off the hour (UTC). LWIS (Limited Weather Information System) is a system that generates additional weather reports outside the hours of human observations.

This chapter describes standards for coding and reporting METAR, SPECI, and LWIS reports. It provides the symbolic code forms of each type of report, followed by detailed descriptions of the code groups and elements that make up a particular code form. Guidance and notes to ensure standard encoding of observed meteorological data are also included.

Aerodrome routine and special reports are also to be disseminated in ICAO meteorological information exchange Model (IWXXM) Geography Markup Language (GML) form in addition to the dissemination of the METAR and SPECI in accordance with the code form otherwise specified in this chapter.

It is emphasized that no meteorological reports shall be issued in the ICAO code form for aerodrome routine and special reports (in METAR / SPECI form as detailed as follows in this Chapter) or be distributed on the Global Telecommunication System (GTS) unless they comply with all requirements for these reports, as establish in Canadian Aviation Regulations standards. This includes including all related meteorological elements, a continuous weather watch resulting in the issuance of special reports when SPECI thresholds are crossed and quality control and management. Further guidance on these requirements can be requested from: Email: TC.ANSWeatherInfo-InfoMeteoSNA.TC@tc.gc.ca

11.2 The METAR and SPECI code

Detailed coding instructions for each element of each group of the METAR and SPECI codes are given below. The type of report is usually determined after all data have been observed. The order in which elements are observed or that entries are made by the observer may differ from the order of the code form below; however, the order in which elements are reported must match the symbolic form. Although the observer may find that some weather elements are automatically encoded, it is still necessary for the observer to have a basic understanding of how these weather elements are encoded.

11.2.1 Symbolic form of the Canadian METAR or SPECI code

( METAR or SPECI ) CCCC YYGGggZ AUTO BBB dddffGfmfmKT dndndnVdxdxdx VVVVSM ( RDRDR/VRVRVRVRFT/i or RDRDR/VRVRVRVRVVRVRVRVRFT/i ) w’w’ ( NsNsNshshshs and/or VVhshshs ) T’T’/T’dT’d APHPHPHPH ( WS RWYDRDR or WS ALL RWY ) RMK (layer type and amount, as well as general remarks) SLPppp

11.2.2 Detailed description

11.2.2.1 Type of reports (METAR or SPECI)

The code name METAR or SPECI shall be included at the beginning of an individual report.

METAR (Aerodrome routine meteorological report) is the code name of the international meteorological code for reporting surface weather observations that are taken and reported on the hour (UTC). METAR contains a report of wind, visibility, runway visual range, present weather, sky condition, temperature, dew-point, and altimeter. In addition, coded and/or plain language information elaborating on weather elements can be found in the “Remarks” section.

SPECI (Aerodrome special meteorological report) is the code name for an unscheduled report transmitted when any of the selected changes in weather conditions significant to aviation occur off the hour (UTC). SPECI shall contain all data elements found in a METAR. In addition, coded and/or plain language information elaborating on weather elements can be found in the “Remarks” section.

11.2.2.2 ICAO station identifier (CCCC)

Four-letter identifier beginning with the letter “C” which identifies it as a Canadian station.

11.2.2.3 Date and time of observation (YYGGggZ)

The date and time of observation (YYGGggZ) shall be included in all reports.
YY: Day of month.
GG: Hour of the day.
gg: Minute of the hour.
Z: Indicates UTC.

11.2.2.4 Automatic station indicator (AUTO)

AUTO: Indicates the report is from an automatic observation station.

11.2.2.5 Correction indicator (BBB)

BBB: Formed by the letters CC preceding an incremented letter to indicate the corrected observation. Use CCA for first correction, CCB for second correction, and so on.

11.2.2.6 Wind velocity (dddffGfmfmKT)

ddd: The two-minute mean wind direction from which the surface wind is blowing. This data is always encoded with three digits.
ff: The two-minute mean wind speed. This data is encoded with two digits if under 100 kt, and with three digits if equal to or over 100 kt.
Gfmfm: Gust information will be included if gust speed criteria are met. If gust criteria are not met, this group shall not be reported. G indicates gust and fmfm is the peak gust speed reported.
KT: Indicates that the units are knots.

11.2.2.7 Variation in wind direction (dndndnVdxdxdx)

dndndn: First counter-clockwise wind direction from the mean wind direction.
V: Variable indicator that is mandatory when this group is reported.
dxdxdx: Last clockwise wind direction from the mean wind direction.

11.2.2.8 Variable wind direction (VRB)

Report variable wind direction as VRB when the criteria for variable wind are met.

11.2.2.9 Prevailing visibility (VVVVSM)

The prevailing visibility is reported in international statute miles and fractions of miles followed by the letters “SM” to indicate units.
VVVV: Prevailing visibility.
SM: Indicates the units are international statute miles.

11.2.2.10 Runway Visual Range (RVR) (RDRDR/VRVRVRVRFT/i)

R: Group indicator that precedes the runway visual range information.
DRDR: Designator of each runway for which runway visual range is reported.
VRVRVRVRFT: The 10-minutes average runway visual range immediately preceding the observation. FT shall be appended to the measurement to indicate that the measurement is in feet.
i: Indicates the RVR trend.

11.2.2.10.1 Variations in runway visual range (RDRDR/VRVRVRVRVVRVRVRVRFT/i)

Variation in the runway visual range shall be given in the form RDRDR/VRVRVRVRVVRVRVRVRFT/i instead of the 10-minute mean.

11.2.2.11 Present weather (w’w’)

One or more w’w’ groups shall be used to report all present weather phenomena observed at or near the aerodrome and of significance to aeronautical operations, in accordance with WMO Code table 4678 (see Table 11—1).

11.2.2.12 Intensity

If the intensity of the phenomena being reported in a group is either light “-” or heavy “+”, this is indicated by the appropriate sign. No sign is included if the intensity is moderate, or when intensity is not relevant.

11.2.2.12.1 Intensity of multiple precipitation types

If multiple precipitation types are observed, the intensity assigned to the group will be that of the predominant precipitation type as determined by the greater intensity. The predominant precipitation shall be reported first within the combined report, except when freezing precipitation occurs. Freezing precipitation shall be reported as a separate group.

11.2.2.13 Priority of present weather groups

Present weather (w’w’) groups shall be reported in the following order:

1. the qualifier for intensity or for proximity (if appropriate), followed without a space by 2)
2. the abbreviation for the descriptor (if appropriate), followed without a space by 3)
3. the abbreviation for the observed weather phenomenon or combinations thereof

Table 11 – 1 shall be used to specify the code figure for w’w’.

11.2.2.14 Layers aloft (NSNSNShShShS)

NSNSNS: The amount of each layer.
hShShS: The height of layers aloft.

11.2.2.15 Vertical visibility (VVhShShS)

VV: Group indicator that precedes the vertical visibility information.
hShShS: Vertical visibility.

11.2.2.16 Temperature/dew-point temperature (T’T’/T’dT’d)

T’T’: Dry-bulb temperature.
T’dT’d: Dew-point temperature.

11.2.2.17 Altimeter setting (APHPHPHPH)

A: Group indicator that precedes the altimeter settings information.
PHPHPHPH: The altimeter setting in hundredths of inches of mercury using four digits.

11.2.2.18 Wind shear in the lower layers (WS RWYDRDR or WS ALL RWY)

WS: Group indicator that precedes the wind shear information
RWYDRDR: RWY is the standard indicator, followed by DRDR which represents the runway designators. As in the case of RVR, the letters “L”, “C”, or “R” may be appended (indicating the left, central or right parallel runway, respectively).
ALL RWY: Is used if the existence of wind shear applies to all runways.

11.2.2.19 Remarks (RMK)

The Remarks portion of the METAR or SPECI observation is used to describe meteorological information of importance. General aviation remarks are referenced in Chapter 10. Directions in Remarks shall be recorded in a clockwise order.

11.2.3 Criteria for reporting SPECI

11.2.3.1 Ceiling

A SPECI report shall be reported whenever ceiling decreases to less than, or increases to equal or exceed (if below), the following coded values of height (in hundreds of feet):

• 15
• 10
• 5
• 4¹
• 3
• 2¹
• 1¹
• any additional limits as specified by the service provider

11.2.3.2 Obstruction to vision

A SPECI report shall be reported whenever freezing fog begins or ends.

11.2.3.3 Sky condition

A SPECI report shall be reported whenever a layer aloft is observed below 1 000 ft and no layer aloft was reported below this height in the immediately preceding report.

11.2.3.4 Visibility

A SPECI report shall be reported whenever prevailing visibility decreases to less than, or increases to equal or exceed (if below), the following values:

• 3 mi.
• 1 ½ mi.
• 1 mi.
• ¾ mi.¹
• ½ mi.
• ¼ mi.¹
• any additional limits as specified by the service provider

11.2.3.5 Tornado, waterspout or funnel cloud

A SPECI report shall be reported whenever a tornado, waterspout or funnel cloud:

• is observed
• is reported from a reliable source
• disappears from sight

11.2.3.6 Thunderstorm

A SPECI report shall be reported whenever a thunderstorm:

• begins
• ends (15 minutes have elapsed without the occurrence of thunderstorm activity)

11.2.3.7 Precipitation

A SPECI report shall be reported whenever any of the following begin, end or change in intensity:

• freezing rain
• freezing drizzle
• ice pellets
• rain
• rain showers
• drizzle
• snow
• snow showers
• snow grains
• hail
• small hailstones
• snow pellets
• ice crystals (begin or end)

A SPECI report shall be reported, as required, to report the beginning and end of each individual type of precipitation, regardless of simultaneous occurrences of other types. A leeway of up to 15 minutes is allowed after the precipitation ends before a SPECI is mandatory.

Changes in the character of precipitation do not require a SPECI if the break in precipitation does not exceed 15 minutes and there is no change to the intensity in the precipitation.

11.2.3.8 Temperature changes

Designated sites¹ are required to issue special (SPECI) reports when temperature changes occur that are of concern to aviation operations. Temperature changes meeting the following criteria shall be reported by all designated sites¹ whenever:

1. the rounded temperature increases by 5 °C or more from the previous reported value and the previous reported value was 20 °C or higher
2. the temperature decreases to a reported value of 2 °C or lower from the previous report

11.2.3.9 Wind changes

A SPECI report shall be reported whenever wind direction or speed changes occur and equal or exceed the following criteria:

1. speed (two-minute mean) increases suddenly to at least double the previously reported value and exceeds 30 kt
2. direction changes sufficiently to fulfill criteria required for a “wind shift” as per section 3.3.3
3. the existence of low-level wind shear along the runway takeoff or approach path 1 500 ft AGL and below, which is considered significant to aircraft operations, shall be reported

11.2.3.10 Volcanic eruption

A SPECI report shall be reported whenever a volcanic eruption is observed. The following data shall be included in Remarks, when known:

1. name of the volcano
2. direction (16 points, true, of the compass) and approximate distance (international statute miles) of the volcano
3. date/Time (UTC) of eruption
4. height and direction of movement of ash cloud
5. other pertinent data

Post-eruption volcanic ash clouds shall be included in the Remarks section of METAR and observations, if significant.

11.2.3.11 Additional observations

The criteria specified in the preceding paragraphs shall be regarded as the minimum requirements for taking SPECI observations. Observers are encouraged to exercise initiative by taking additional observations when any weather condition exists that may impact the safety and efficiency of aircraft operations or is considered to be otherwise significant. This is to ensure that significant changes in weather are reported. Additional observations shall be reported as a SPECI:

• on request of a forecast centre
• on request of Air Traffic Services (ATS)
• based upon an observer’s initiative
• upon notification of an aircraft accident
• based on local criteria as define by service providers

11.3 The LWIS code

11.3.1 General information

The Limited Weather Information System (LWIS) generates additional weather reports outside the hours of human observations. These reports provide wind, temperature, dew-point and altimeter setting information. The LWIS information is updated on an hourly basis.

11.3.2 Symbolic form of the LWIS code

LWIS CCCC YYGGggZ AUTO dddffGfmfmKT T’T’/T’dT’d APHPHPHPH

11.3.3 Detailed description

11.3.3.1 Type of report

The code name LWIS shall be included at the beginning of an individual report.

11.3.3.2 ICAO station identifier (CCCC)

See section 11.2.2.2.

11.3.3.3 Date and time of observation (YYGGggZ)

See section 11.2.2.3.

11.3.3.4 Automatic station indicator (AUTO)

See section 11.2.2.4.

11.3.3.5 Wind velocity (dddffGfmfmKT)

See section 11.2.2.6.

11.3.3.6 Temperature/dew-point temperature (T’T’/T’dT’d)

See section 11.2.2.16.

11.3.3.7 Altimeter setting (APHPHPHPH)

See section 11.2.2.17.

Chapter 12. Automatic system standards

12.1 General information

This chapter explains what an automated observing and reporting system is and outlines the standards for observations, reports, and instruments when using an automated system. Examples of remarks to be used for weather elements are provided. This chapter applies to service providers who provide aviation weather services consisting of automated observation and reporting of any or all of the following: wind direction, speed and character; visibility, RVR, present weather, sky condition, temperature, dew-point temperature, atmospheric pressure and remarks.

12.2 Standards for observations, reports, and instruments

12.2.1 Wind standards

Meteorological observations of surface wind shall meet the following standards:

1. The wind measurements shall be representative of winds that are 10 m above the ground over level terrain at a distance equal to at least 10 times the height of any object from that object or, if this is not possible, at such a height and location that the indications are reasonably unaffected by local obstructions
2. The instruments shall function for winds of up to and including at least 100 kt speed
3. The accuracy of wind sensors and wind reports shall be such that:
   1. the direction is correctly reported within ± 10°
   2. the mean speed is correctly reported within ± 2 kt up to 20 kt, and within 10% of the mean speed above 20 kt
4. The wind measurement shall include:
   1. direction
   2. speed
   3. character (if applicable)
5. The wind direction from which the wind is blowing and the wind speed shall be averaged over a two-minute period
6. The wind direction from which the wind is blowing shall be reported in tens of degrees with reference to true North
7. For voice communication purposes in support of take-off or landing operations in the Southern Domestic Airspace wind direction shall be reported in tens of degrees with reference to magnetic North
8. The wind speed shall be reported in knots
9. Calm wind may be reported for mean wind speeds less than 2 kt and 1 kt or less shall be reported as calm wind
10. The wind character shall be reported as a “gust” if wind speed data for the most recent ten minutes indicate rapid fluctuations in wind speed and:
    1. a peak wind speed that exceeds the current two-minute mean wind speed by 5 kt or more
    2. the highest peak wind speed is at least 15 kt
11. The speed of a gust shall be the maximum wind speed, in kt, averaged over a maximum of a five-second period
12. The wind character shall be reported as a “squall” if wind speed increases by 15 kt or more over the two-minute average speed that preceded the increase and:
    1. the duration of the peak speed period is at least two minutes
    2. the wind speed attains a one-minute mean of at least 20 kt, during the peak speed period
    3. the wind speed diminishes by at least 5 kt
13. When squalls are observed, “SQ” shall be reported in present weather and:
    1. the peak wind speed shall be reported as a gust (the speed to be reported is the highest one-minute mean speed)
14. Variations from the mean wind direction where the total variation is 60° or more during the past 10‑minutes period shall be reported as follows:
    1. when the total variation is between 60° and 180° and the wind speed is 3 kt or more, such directional variation shall be reported as the two extreme directions in clockwise order between which the surface wind has varied
    2. when the total variation is between 60° and 180° and the wind speed is less than 3 kt, the wind direction shall be reported as variable with no mean wind direction
    3. when the total variation is 180° or more, the wind direction shall be reported as variable with no mean wind direction.

12.2.1.1 Examples of wind remarks

Wind remarks may be automatically generated by the wind measurement system. Use WIND MISG when wind data is not available.

12.2.2 Visibility standards

12.2.2.1 Observations and reports

The observation of visibility shall meet the following requirements:

1. If the visibility cannot be determined, then it shall be reported as missing (VIS MISG)
2. The reportable values of visibility shall be:
   1. 0, ⅛, ¼, ⅜, ½, ⅝ and ¾ of an international statute mile for visibility up to but not including 1 mi.
   2. by increments of ¼ mi. for visibility of 1 mi. up to and including 2 ½ mi.
   3. increments of 1 mi. from 3 mi. up to and including 15 mi.
   4. increments of 5 mi. above 15 mi. onward
3. If the observed value of visibility is between two reportable values, then the lower value shall be reported

12.2.2.2 Instruments

Instruments used for the measurement of visibility shall meet or exceed the following standards:

1. Instruments shall incorporate a background luminance sensor that is accurate to within 10% with a confidence level of at least 90%
2. The Meteorological Optical Range, as defined by the World Meteorological Organization, shall:
   1. be determined within ¼ mi. of the value of a reference transmissometer (instrument for measuring the extinction coefficient of the atmosphere, and for the determination of visual range) from ¼ mi. to 1 mi. at least 80% of the time
   2. be determined within ¼ mi. above and within ½ mi. below the value of a reference transmissometer, or clinical human observations (qualified meteorological observers) from 1 ¼ mi. to 1 ¾ mi. at least 80% of the time
   3. be determined within ± ½ mi. of the value of a reference transmissometer, or clinical human observations, from 2 mi. to 2 ½ mi. at least 80% of the time
   4. be determined within ½ mi. above or within 1 mi. below the value of a reference transmissometer, or clinical human observations, from 3 mi. to 3 ½ mi. at least 80% of the time
   5. be determined within ± 1 mi. of the value of a reference transmissometer, or clinical human observations, from 4 mi. to 6 mi. at least 80% of the time
   6. meet criteria established and documented by the service provider for visibility greater than 6 mi.

12.2.2.3 Examples of visibility remarks

Visibility remarks are automatically generated by the visibility measurement system. Use the remark VIS MISG when wind data is not available.

12.2.2.4 Runway Visibility Range (RVR)

Runway visibility range is reported at sites equipped with RVR sensors; refer to Chapter 5 Runway visual range (RVR).

12.2.3 Present weather standards

12.2.3.1 Instruments

The observation of present weather shall meet or exceed accuracy standards, as follows, with reference to clinical human observations:

1. Instruments shall correctly detect the presence of precipitation at water equivalent rate of at least 0.2 mm per hour, other than drizzle, at least 90% of the time
2. Instruments shall correctly report the presence of and distinguish between liquid or frozen precipitation, at a water equivalent rate of at least 0.2 mm per hour, at least 80% of the time
3. Instruments shall correctly report at least a 90% probability of detection of the presence of ice
4. Instruments shall correctly detect and differentiate rain, freezing rain and snow, and (as applicable) determine the intensity (except as permitted in accordance with 8)
5. Instruments shall correctly report accretion or freezing precipitation of at least light intensity
6. Should five or more thunderstorm days per year be expected given the climatology of the site, then it is necessary for a station to be able to correctly detect and report, with at least an 80% probability, thunderstorms within 6 mi. of the station
7. Instruments shall correctly report the presence of thunderstorm in the vicinity (VCTS), if lightning is detected from greater than 6 mi. to 10 mi.
8. Instruments shall indicate unknown precipitation type as UP if the type cannot be determined

12.2.3.2 Examples of present weather remarks

Remark to use when icing data missing: ICE MISG
Remark to use when precipitation data missing: PCPN MISG
Remark to use when thunderstorm/lighting data missing: TS/LTNG TEMPO UNAVBL
Remark to use when weather data missing: WX MISG
Remark to use if lightning is detected between 10 to 30 mi. with octant compass cardinal direction: LTNG DIST
Remark to use if lightning is detected in four or more octants: LTNG DIST ALQDS

12.2.4 Sky condition standards

12.2.4.1 Observations and reports

The following standards shall apply to observations and reports of sky condition:

1. The reportable values of cloud base or vertical visibility into an obscuring layer shall be:
   1. in increments of 100 ft up to and including 10 000 ft
   2. in increments of 1 000 ft above 10 000 ft
2. If the observed value of the base of a cloud layer or vertical visibility into an obscuring layer is between two reportable values, then the lower value shall be reported
3. If the observed cloud amount is between two reportable values, then the greater value shall be reported
4. For aerodromes, the cloud base height or vertical visibility into an obscuration shall be given with reference to the aerodrome elevation as published in the Canada Flight Supplement, except:
   1. when the height of the precision approach runway is 50 ft or more below aerodrome elevation
   2. local arrangements shall be made so that the height of cloud bases reported to arriving aircraft refers to the threshold elevation
   3. in the case of reports from offshore structures, when the height of cloud base shall be given above mean sea level
5. When no clouds are detected beyond the limit of the automatic observing system, it shall be indicated by using the abbreviation NCD or CLR BLO 250

12.2.4.2 Instruments

Instruments used for the measurement of sky condition shall meet or exceed the following standards:

1. Instruments shall incorporate an algorithm that is equivalent to or better than the United States Federal Aviation Administration standard algorithm for ceilometers or demonstrate that an alternative method performs as well or better than this algorithm
2. Instruments shall use the aerodrome elevation as published in the Canada Flight Supplement as the reference elevation to compute cloud base height or vertical visibility
3. Instruments shall have accuracy such that the distance to a solid target is measured to within the greater of 100 ft or 5% up to 10 000 ft with a confidence level of at least 95%; and
   1. within one reportable value of the ceiling value reported by a clinical human observer at least 75% of the time up to and including 900 ft
   2. within two reportable values of the value of the base of the ceiling reported by a clinical human observer at least 70% of the time from 1 000 to 2 500 ft

12.2.4.3 Examples of sky condition remarks

When sky condition (cloud) data is missing: CLD MISG

12.2.5 Temperature and dew-point standards

12.2.5.1 Observations and reports

The following standards shall apply to observations and reports of temperature and dew-point:

1. Meteorological observations of temperature shall be accurate to within 1 °C
2. Meteorological observations of dew-point temperature shall be accurate to within 2 °C for dew-point temperatures ranging from –30 °C to +25 °C
3. The temperature shall be reported to the nearest whole degree Celsius, with observed values involving 0.5 °C being rounded up to the next warmer whole degree Celsius

12.2.5.2 Instruments

The accuracy requirements shall be demonstrated with at least a 95% confidence level during laboratory testing that is traceable to a reference standard.

12.2.5.3 Examples of temperature remarks

Remark to use when temperature data is missing: T MISG
Remark to use when dew-point temperature data is missing: DP MISG

12.2.6 Atmospheric pressure (altimeter setting) standards

12.2.6.1 Observations and reports

Meteorological observations of atmospheric pressure intended to be provided as meteorological reports of altimeter setting shall be measured by a digital barometer containing two or more independently sensors and that has quality checks that, in the event of sensor failure, prevent the report from being issued. A barometer for aviation purposes shall contain two or more independently operating sensors, each of which is traceable to a WMO primary standard barometer.

The following standards shall apply to reports of atmospheric pressure:

1. The calculated altimeter setting shall be:
   1. Computed from the station pressure using the International Civil Aviation Organization (ICAO) Standard Atmosphere and the aerodrome reference elevation in the Canada Flight Supplement
   2. Rounded downward to the nearest one hundredth inch of mercury for reporting purposes
   3. The computed sea level pressure shall be reported in observations so that the barometric pressures at stations of different elevations can be compared at a common level for synoptic purposes

12.2.6.2 Instruments

Instruments used for the measurement of pressure shall meet or exceed the following standards:

1. The sensors shall be installed and operated in accordance with the manufacturer’s specifications, or equivalent specifications developed by the service provider
2. The sensors shall be accurate to within 0.02 inHg (inch of mercury)
3. The accuracy requirement shall be demonstrated with at least a 95% confidence level in laboratory testing

12.2.6.3 Examples of pressure remarks

Remark to use when pressure (altimeter) data is missing: PRES MISG
This remark is only added when the density altitude is 200 ft or higher than the aerodrome elevation: DENSITY ALT XXXFT
Remark to use when density altitude is missing: DENSITY ALT MISG
Remark to use when sea level pressure is missing: SLP MISG

12.2.7 AUTO SPECI Standards for observations and reports

Each automated observation program providing METAR AUTO reports shall ensure that SPECI reports are reported upon changes in the weather, relative to the current report, in accordance with the following:

1. A SPECI is issued when the mean surface wind direction has shifted by 45º or more in less than 15 minutes and the wind speed at the end of the shift is at least 10 kt
2. A SPECI is issued when the two-minute mean wind speed increases by 10 kt or more
3. A SPECI is issued when the lesser of the vertical visibility into a totally obscuring surface based layer, or the height of the lowest broken or overcast layer aloft, decreases to less than, or if below, increases to equal or exceeds any of the following heights:
   1. 2 500 ft
   2. the threshold between IFR (Instrument Flight Rules) and VFR (Visual Flight Rules) ceiling 1 000 ft
   3. the aerodrome specific alternate minima for ceiling in accordance with the alternate weather requirements table in the most recent Canada Air Pilot
4. A SPECI is issued when a cloud layer aloft is observed below 1 000 ft and no cloud layer was reported below that height in the immediately preceding report
5. A SPECI is issued when visibility decreases to less than, or if below, increases to equal or exceeds:
   1. the no-alternate IFR limit, where applicable
   2. the threshold between IFR and VFR; (visibility 1 mi.)
   3. the aerodrome specific alternate minima for visibility in accordance with the alternate weather requirements table in the Canadian Flight Supplement
6. A SPECI is issued upon a change in the intensity of freezing precipitation
7. A SPECI is issued when hail, freezing fog, freezing rain, rain, snow, thunderstorms or heavy precipitation of any type begin or end
8. A SPECI is issued for the onset or cessation of precipitation of at least light intensity
9. A SPECI is issued for the onset or cessation of ice accretion
10. A SPECI is issued in accordance with any additional criteria as established and documented by the service provider

The service provider shall document the criteria used for the issuance of SPECI, in accordance with the applicable requirements of items 1) to 10) of this section.

Chapter 13. Glossary of Terms

13.1 General information

This chapter provides definitions of terms used in this manual.

13.2 Glossary

13.2.1 Altimeter setting

The altimeter setting is a computed value of mean sea-level pressure expressed in inches and hundredths of mercury, which is used to set the sub-scale of an altimeter so that the height scale of the altimeter indicates the height of the instrument above mean sea level. Altimeter setting is done in accordance with the ICAO Standard Atmosphere.

13.2.2 ANS (Air Navigation Services)

Air navigation services is the term applied to the bundle of services provided to aircraft to enable safe and efficient flight from one destination to another.

13.2.3 CARs (Canadian Aviation Regulations)

The Canadian Aviation Regulations are a compilation of regulatory requirements designed to enhance safety and the competitiveness of Canadian aviation.

13.2.4 Climatological day

The climatological day summarizes the 24-hour period ending at 0600 UTC which contains all the following elements: the date, maximum and minimum temperature, maximum and minimum relative humidity, six-hour amount of precipitation, 24-hour amount (rainfall, snowfall, total precipitation), depth of snow on the ground, day with occurrence of thunderstorms, precipitation, obstructions to vision, and strong winds.

13.2.5 Funnel cloud or cold-air funnel

Funnel clouds, or (rarely) small, relatively weak tornadoes, can develop from a small shower or thunderstorm when the air aloft is unusually cold. Cold-air funnels typically do not reach the ground (funnel cloud), but when they do reach the ground as tornadoes, they are much less violent than the other types.

13.2.6 ICAO (International Civil Aviation Organization)

The International Civil Aviation Organization is a UN specialized agency, established by States in 1944 to manage the administration and governance of the Convention on International Civil Aviation (Chicago Convention). ICAO works with the Convention’s 192 Member States and industry groups to reach consensus on international civil aviation “Standards And Recommended Practices” (SARPs) and policies in support of a safe, efficient, secure, economically sustainable and environmentally responsible civil aviation sector.

13.2.7 ICAO station identifier

Four-letter identifier beginning with the letter “C”, which identifies a Canadian weather observing station.

13.2.8 Mean sea level pressure

Mean sea level pressure is computed from the station pressure and reported in observations so that the barometric pressures at stations of different elevations can be compared at a common level for synoptic purposes.

13.2.9 Obstructions to vision

The following are types of obstructions to vision:

• Blowing Dust or Blowing Sand: This obstruction to vision consists of dust or sand, raised by the wind to moderate heights above the ground
• Blowing Snow: This obstruction to vision consists of snow particles raised by the wind to sufficient heights above the ground to reduce the horizontal visibility at eye level to 6 mi. or less
• Dust Haze: This obstruction to vision is produced by the suspension in the air of dust or small sand particles, raised from the ground, prior to the time of observation, by a dust storm or sandstorm
• Dust storm: This obstruction to vision is produced by dust raised to great heights by a strong turbulent wind. The forward portion of the storm may have the appearance of a wide high wall
• Dust/Sand Whirls: This obstruction to vision, commonly known as a dust devil, consists of an ensemble of particles of dust or sand, sometimes accompanied by small litter, raised from the ground by the wind, in the form of a whirling column of varying height with a small diameter and an approximately vertical axis
• Fog: This obstruction to vision is formed by the suspension of very small water droplets or ice crystals in the air, reducing the visibility to ½ mi. or less at the earth’s surface. The ice crystals in the fog may produce phenomena such as small haloes and luminous pillars around lights, the sun or the moon.
• Freezing fog: This obstruction to vision consists mainly of super-cooled droplets that usually deposit rime or glaze on objects or surfaces with below freezing temperatures. The definition of freezing fog is the same as for fog, except that it occurs when the temperature is in the range of ‑0.1 °C to -30.0 °C and the visibility is ½ mi. or less. It may be reported at temperatures colder than -30.0 °C when there is clear physical evidence of ice accretion from the fog and the visibility is ½ mi. or less.
• Haze: This obstruction to vision consists of a suspension of extremely small, dry particles invisible to the naked eye and sufficiently numerous to give the air an opalescent (milky or pearly) appearance
• Mist: The definition of mist is the same as for fog, except that mist reduces visibility to the range ⅝ mi. to 6 mi. inclusive
• Fog covering part of aerodrome: Consists of a fog bank or area of fog (or freezing fog) which may have small breaks, however within the area of fog at least 50% of the ground must be covered (see Appendix 2)
• Fog patches: Consists of fog extending to at least 1.5 m above ground level with a coverage of less than 50% of the ground normally visible from the observing point (see Appendix 2)
• Shallow fog patches: A suspension of very small water droplets in the air, reducing the visibility at the earth’s surface, but not appreciably reducing the visibility at eye level (see Appendix 2)
• Sand storm: This obstruction to vision is produced by sand raised to great heights by a strong turbulent wind. The forward portion of the storm may have the appearance of a wide high wall.
• Smoke: A suspension in the air of small particles produced by combustion
• Volcanic Ash: Volcanic ash consists of fine particles of rock powder that have been blown out from a volcano. The ash may remain suspended in the atmosphere for long periods, producing red sunsets thousands of kilometres away.

13.2.10 Other hydro-meteorological deposits

The following are other forms of hydro-meteorological deposits:

• Dew: This deposit forms when water is condensed on grass and other objects near the ground. The surface on which the dew forms has been cooled by radiation during the night, to a temperature below the dew-point of the surrounding air, but is still above freezing
• Glaze: This deposit is a coating of ice, generally clear and smooth, formed on exposed objects by the freezing of a film of super cooled water deposited by rain, drizzle, fog or possibly condensed from super cooled water vapour. Glaze is denser, harder and more transparent than either rime or frost.
• Hoar frost: This deposit, commonly called frost, forms when air with a dew-point temperature below freezing is brought to saturation by cooling. Hoar frost is a deposit of interlocking ice crystals formed by direct sublimation on objects, usually of small diameter, such as tree branches, plant stems, leaf edges, wires, and poles.
• Rime: This deposit is a white or milky and opaque “granular” deposit of ice formed by the rapid freezing of super-cooled water drops as they contact an exposed object

13.2.11 Pilot reports

Reports of weather conditions encountered by aircraft during flight.ny important atmospheric phenomenon encountered between reporting points should be reported, either immediately or appended to the position report given over the next reporting point. Pilot reports received by flight service personnel are relayed on meteorological communications circuits to weather offices and other air traffic service units. Pilot reports are no longer a part of MANOBS.

13.2.12 Precipitation

Any product of the condensation of atmospheric water vapour that is deposited on the earth’s surface is a type of precipitation. The types of precipitation that originate aloft are classified under liquid precipitation, freezing precipitation, and frozen precipitation.

13.2.13 Precipitation (freezing)

The following are forms of freezing precipitation:

• Freezing Drizzle: Drizzle, the drops of which freeze on impact with the ground or with other objects at or near the earth’s surface¹
• Freezing Rain: Rain, the drops of which freeze on impact with the ground or with other objects at or near the earth’s surface¹

13.2.14 Precipitation (frozen)

The following are forms of frozen precipitation:

• Hail: Precipitation of small balls or pieces of ice (hailstones) with a diameter ranging from 5 mm to 50 mm or sometimes more, and which fall either separately or fused into irregular lumps. Hailstones are composed almost exclusively of transparent ice, or of a series of transparent layers of ice at least 1 mm in thickness, alternating with translucent layers. Hail is generally observed during severe thunderstorms. Small hailstones meet the above but, the diameter of the largest stones are smaller than 5 mm.
• Small hailstones: Precipitation of small balls or pieces of ice (hailstones) with a diameter smaller than 5 mm, and which fall either separately or fused into irregular lumps. Hailstones are composed almost exclusively of transparent ice, or of a series of transparent layers of ice at least 1 mm in thickness, alternating with translucent layers.
• Ice Crystals: A fall of non-branched ice crystals, in the form of needles, columns or plates, often so tiny that they seem to be suspended in the air. These crystals may fall from cloud or from a cloudless sky. The crystals are visible mainly when they glitter in the sunshine; they may then produce a luminous pillar or other halo. This hydrometeor, which is frequent in Polar Regions, occurs only at very low temperatures and in stable air masses. In WMO terminology, ice crystals are referred to as “diamond dust.”
• Ice Pellets: Precipitation of transparent or translucent pellets of ice that are spherical or irregular, rarely conical, having a diameter of 5 mm or less. Ice pellets are subdivided into two main types:
  • Frozen raindrops, or snowflakes that have largely melted and then refrozen, the freezing process usually taking place near the ground (they generally fall as continuous precipitation)
• Snow Grains: Precipitation of very small white and opaque grains of ice. These grains are fairly flat or elongated; their diameter is generally less than 1 mm. When the grains hit hard ground, they do not bounce or shatter. They usually fall in very small quantities, mostly from Stratus or occasionally from fog, and never in the form of a shower.
• Snow Pellets: Precipitation of white and opaque particles of ice; these ice particles are either spherical or conical; their diameter is about 2 mm to 5 mm. Snow pellets are brittle and easily crushed; when they fall on hard ground, they bounce and often break up. Snow pellets always occur in showers and are often accompanied by snowflakes or rain drops, when the surface temperature is around 0 °C.
• Snow: Precipitation of mainly hexagonal ice crystals, most of which are branched (star-shaped). The branched crystals are sometimes mixed with unbranched crystals. At temperatures higher than about -5 °C, the crystals are generally clustered to form snowflakes.

13.2.15 Precipitation (liquid)

The following are forms of liquid precipitation:

• Drizzle: Fairly uniform precipitation composed exclusively of fine drops of water (diameter less than 0.5 mm). Drizzle drops are too small to cause appreciable ripples on the surface of still water. The drops appear almost to float in the air, making visible even slight movements of the air. Drizzle falls from fairly continuous and dense layers of Stratus, usually low, sometimes even touching the ground (fog).
• Rain: Precipitation of liquid water particles, either in the form of drops of larger diameter than 0.5 mm, or of smaller widely scattered drops. Rain drops are normally larger than drops of drizzle; nevertheless, drops falling on the edge of a rain zone may be as small as drizzle drops, owing to partial evaporation.

13.2.16 Station elevation

The station elevation is the vertical distance in metres above Mean Sea Level (MSL) of the datum level to which barometer readings are corrected to give station pressure.

13.2.17 Thunderstorm

A thunderstorm is a local storm produced by a Cumulonimbus cloud, and is always accompanied by lightning and thunder, usually with strong gusts of wind, heavy rain, and sometimes with hail.

13.2.18 Tornadoes

Tornadoes are rotating columns of air, extending from the base of a cumuliform cloud (usually Cumulonimbus), and often visible as a condensation funnel in contact with the ground, and/or attendant circulating dust or debris cloud at the ground.

13.2.19 Waterspouts

Waterspouts are tornadoes that occur over water. They are normally a relatively small, weak rotating column of air over open water below a Cumulonimbus or Cumulus congestus (towering Cumulus) cloud.

13.2.20 Visibility reduced below eye level

Drifting dust (DRDU), drifting sand (DRSA) and drifting snow (DRSN) are phenomena which reduce visibility below eye level. When particles of dust, sand or snow are raised by the wind in such a quantity that very low objects are veiled or hidden and yet the visibility at eye level is not appreciably restricted, the phenomenon is referred to as drifting dust, drifting sand or drifting snow, respectively.

Part B Standards for synoptic observations and reports

Chapter 14. The synoptic code – general description

14.1 General information

This chapter provides a general description of the international meteorological code FM 12-XIV Ext. SYNOP. The symbolic form of the synoptic code is given, followed by general operational details for reporting synoptic surface weather observations from land stations.

14.1.1 Purpose of synoptic reports

Weather recognizes no international boundaries. A precise synoptic picture of weather conditions over a vast area of the earth’s surface is required in order to provide national and international forecasts and climatological data to satisfy the needs of aviation, agriculture, industry and the public. As a first step in meeting these requirements, surface weather reports are prepared and exchanged throughout the world in an international code developed and agreed upon by member states of the World Meteorological Organization (WMO). Such reports are made at least four times daily and a complete report may contain over 20 pieces of information including measurements of atmospheric pressure, calculated from barometer readings taken at precisely the same time throughout the world, i.e., 0000 UTC, 0600 UTC, 1200 UTC and 1800 UTC. These observations are referred to as synoptic observations.

14.2 The synoptic code

The international meteorological code “FM 12-XIV Ext. SYNOP” is used for reporting synoptic surface weather observations from a land station, either staffed or automatic. The common synoptic code comprises six sections numbered 0 to 5, each of which is primarily composed of five-figure code groups. Most groups in sections 0 to 5 begin with a numerical indicator and these indicators are numbered consecutively within each section. The numerical indicators identify a specific group which always contains the same weather elements. Thus the omission, whether accidental or deliberate, of any one group will not affect the identification of other groups. Indeed, provision is made within the code for omission of groups when their weather elements are either not present or cannot be observed. This also ensures that the code is flexible enough for both staffed and automatic stations.

14.2.1 Symbolic form of the synoptic code

Within a given five-figure code group, the relative position of each code figure, denoting a specific weather element, is constant; thus the synoptic code can be represented symbolically as depicted below.

Section 0

SYNOP MiMiMjMj YYGGiw IIiii

Section 1

iRixhVV Nddff ( 00fff ) 1snTTT 2snTdTdTd 3P0P0P0P0 4PPPP 5appp 6RRRtR 7wwW1W2 8NhCLCMCH 9GGgg

Section 2 (not reported by land stations)

Section 3

333 [ 0CSDLDMDH ] 1snTxTxTx 2snTnTnTn [ 3Ejjj ] 4E'sss [ 5EEEiE ]
[ 55SSS j5F24F24F24F24 ] 6RRRtR 7R24R24R24R24 [ 8NsChshs ] 9SPSPspsp

Section 4 (not reported in Canada)

Section 5

555 1ssss 2swswswsw 3dmdmfmfm 4fhftftfi

14.2.2 Interpretation of the symbols

Details and interpretation of each code group and their respective symbols are given in Chapter 15. However, only those sections and code groups which apply to Canadian surface weather observing program standards are detailed.

14.2.3 Content of the coded synoptic message

Main synoptic messages from land stations will normally consist of sections 0, 1, and 3. While some groups are mandatory and must be reported in each synoptic message, other groups may be omitted, depending on specified conditions. At land stations, the communications computer will normally insert the first two groups of Section 0; the observer will code and transmit the remainder of the message. Descriptions of mandatory and optional groups as well as detailed coding instructions follow in Chapter 15.

14.2.3.1 Message separation signal (=)

The message separation signal = shall be included as the last character of the last group of each reported synoptic message. The separation signal is always added to the last data group without a space intervening; thus the last group of the reported synoptic message will consist of six characters.

14.2.3.2 Missing data

Elements of missing data are recorded by means of an “X”. When entering a synoptic report on a computer or communication system for transmission, replace an “X” with a solidus “/”.

14.2.4 Observing schedule

The times of the main synoptic reports are 0000, 0600, 1200 and 1800 UTC. In all cases, the barometer shall be read at the hour. The observing, recording and coding of all elements, except the pressure and tendency, should be done in the 10 minutes preceding the hour. In difficult weather it may be necessary to begin 15 minutes before the hour in order to be ready to read the barometer at the hour. All stations shall conform to this schedule of observing, unless special permission to deviate is obtained from the ADM.

Chapter 15. The synoptic code – detailed description

15.1 General information

This chapter provides a detailed description of the international meteorological code FM 12-XIV Ext. SYNOP. A description and the symbolic form of sections 0, 1, 3, and 5 of the synoptic code are provided, followed by section content. Within each section’s code group, a detailed interpretation of all particular symbols is given. Detailed descriptions of Section 2 and Section 4 of the synoptic code are both omitted as these sections are, respectively, not used by surface weather stations and not used within Canada.

15.2 Section 0—Reporting identification and units of wind speed used

In the case of land stations (SYNOP report), Section 0 contains the station identifier. It also contains a message type identifier group and a date-time-wind indicator group which is reported once at the beginning of a synoptic message bulletin.

15.2.1 Symbolic form

SYNOP MiMiMjMj YYGGiw IIiii

15.2.2 Section content

Section 0 is mandatory for all synoptic reports. For land stations, MiMiMiMi and YYGGiw will normally be coded and inserted by the communications computer, whereas IIiii will always be coded by the observer. Other groups in Section 0 are for the identification and location of sea stations, and are not used by land stations.

15.2.3 Interpretation of group MiMiMjMj

This group identifies what type of message is being reported. It is the first group of the second line of the message header. This group is inserted by the communications computer in the message header for identification of synoptic bulletins and is encoded AAXX for synoptic reports from land stations.

15.2.4 Interpretation of group YYGGiw

This group is inserted by the communications computer as the second group of the second line of the message header of a synoptic bulletin originating from a land station.

15.2.4.1 YY—Day of the month (UTC)

The symbol YY indicates the day of the month on which the observation is made.

15.2.4.2 GG—Hour of the observation (UTC)

The symbol GG indicates the actual time of the observation to the nearest synoptic hour UTC.

15.2.4.3 iw – Wind indicator

The symbol iw indicates whether the wind speed is estimated or is measured by means of an anemometer, and whether the wind speed as reported in the message is in units of metres per second, or knots. Table 15—1 specifies code figures used for indicating the source and units of wind speed. The communications computer will insert the code figure 4 for iw at Canadian land stations.

15.2.5 Interpretation of group IIiii

15.2.5.1 II – Block number

All Canadian land stations use 71 or 73 for the block number.

15.2.5.2 iii – Station number

The station number is found in METSTAT (Meteorological Stations of Canada).

15.3 Section 1 – Reporting data for global exchange

Section 1 contains data for international as well as regional and national exchange.

15.3.1 Symbolic form

iRixhVV Nddff (00fff) 1snTTT 2snTdTdTd 3P0P0P0P0 4PPPP 5appp 6RRRtR 7wwW1W2 8NhCLCMCH 9GGgg

15.3.2 Section content

Standards for inclusion of groups in Section 1 are as follows:

1. Groups iRixhVV, Nddff, 1snTTT, 2snTdTdTd, 3P0P0P0P0, 4PPPP and 5appp shall always be included
2. Group 00fff shall be included only if wind speed equals or exceeds 99 kt
3. Group 6RRRtR shall always be included in the message
4. Group 7wwW1W2 shall be included only if present or past weather of significance is observed
5. Group 8NhCLCMCH shall be included only if clouds are observed

15.3.3 Interpretation of group iRixhVV

15.3.3.1 iR – Precipitation group indicator

The symbol iR is an indicator to show whether or not the precipitation group 6RRRtR is included in the message and, if included, in what section of the message it appears. Table 15 – 2 shall be used to specify the code figure for iR.

Code figures 0 and 3 are not used for iR in Canada. At stations normally measuring precipitation, the group 6RRRtR is always included in Section 1 with iR being encoded 1 at main synoptic hours. At stations normally measuring precipitation, the group 6RRRtR is always included in Section 3 with iR being encoded 2 at intermediate synoptic hours.

15.3.3.2 iX – Station type indicator

The symbol iX indicates whether the synoptic message has originated from a staffed or an automatic station and, secondly, whether or not the present and past weather group, 7wwW1W2, is included. Table 15 – 3 shall be used to specify the code figure for iR.

15.3.3.3 h – Base of lowest cloud

The symbol h indicates the height above ground of the base of the lowest cloud observed. When CL clouds exist, the height of the base of the lowest layer is reported by h. When no CL clouds exist, h is coded with reference to the height of the base of the lowest CM cloud. Table 15 – 4 shall be used to specify code figures for h.

15.3.3.4 VV – Visibility

The symbol VV is used to indicate visibility. Table 15—5 shall be used to specify code figures for VV.

15.3.4 Interpretation of group Nddff

15.3.4.1 N – Total cloud amount

The symbol N indicates the fraction of the celestial dome covered by clouds, irrespective of their type. Table 15 – 6 shall be used to specify the code figures for N corresponding to the fraction of the celestial dome covered by clouds in oktas.

15.3.4.1.1 Instructions for coding N when the sky is partially obscured by a surface-based layer

Normally N shall be coded with reference to total amount. However, because of some differences in the procedures for coding hourly and synoptic observations, some further instructions are necessary as indicated in the paragraphs that follow.

When blue sky or stars are seen through a layer of fog or other obscuring phenomenon without any trace of cloud above this layer, N is reported as 0.

If clouds are seen through fog or other obscuring phenomenon, their amount shall be evaluated as though the obscuration did not exist. In other words, partial obscuration may be disregarded and N is determined by considering that portion of the sky which is not obscured to be the entire sky.

Example (1): The sky is partially concealed by fog. In the portion that is not concealed, there are equal parts of blue sky and cloud; the code for N would be 4 (4 oktas) in each case (i.e., in coding N the sky is considered to be half covered by cloud)

Example (2): The sky is partially concealed or obscured by snow. The observer notes that the remainder of the sky is 20% clear and 80% cloud covered. In coding N the sky is considered to be 80% covered by cloud; hence the code for N would be 6.

Example (3): The observer reports only a trace of cloud. Total amount is 0, but since cloud is present, the code for N would be 1.

Example (4): The sky is partially concealed by blowing snow. In the portion that is not concealed, there is no cloud. The code for N would be 0 (i.e., in coding N the sky is considered to be clear).

With a mackerel sky (AC or SC perlucidus), breaks between the cloud elements always exist. Hence, even though these clouds extend over the whole celestial dome, the total amount shall be reported as N = 7 or less.

N = 9 shall be reported when the sky is completely concealed by an obscuring phenomenon, either surface-based or aloft. This instruction also applies when:

• clouds cover part of the sky below the vertical visibility or below an obscuring layer aloft
• clouds are present below the extent of vertical visibility in a surface-based layer which has a summation amount of 8/8

Persistent condensation trails and cloud masses which have obviously developed from condensation trails shall be reported as cloud and considered when coding the cloud amount, N. Rapidly dissipating condensation trails shall not be considered in coding N.

If the sky is partially obscured by a surface-based layer, the code for N may be obtained from Table 15—7. Determine the total amount of cloud and the total amount of sky being obscured in oktas. After determining these values, use the left side of the table for the total amount of cloud and move to the right until the value of the sky obscured is reached. The figure obtained is the code figure.

15.3.4.2 dd – Mean wind direction

The symbol dd indicates the 10‑minute mean direction referred to true north from which the wind is blowing, expressed in tens of degrees on a scale from 00 to 36. Code figures 00 are used when the wind is calm. Code 01 = N 10° E (010°), and so on in ten degree steps through 09 = East (090°), 18 = South (180°), 27 = West (270°), around to 36 = North (360°). 99 = Variable direction (not used when the wind speed is more than 5 kt). Table 15—8 shall be used to specify code figures for dd.

15.3.4.3 ff – Mean wind speed

The symbol ff indicates the 10-minutes mean speed of the wind in knots. When the wind is calm, ff is coded 00. If the wind speed equals or exceeds 99 kt (which may occur in a hurricane) ff is coded 99 and the additional group 00fff is added immediately following Nddff (see 15.3.5). Table 15 – 9 is provided for conversion of miles per hour to knots.

For example: 10 mph = 9 kt; 11 mph = 10 kt; 34 mph = 30 kt; 35 mph = 30 kt; 110 mph* = (87 kt + 9 kt) = 96 kt

15.3.5 Interpretation of group 00fff

This supplementary group is included in all synoptic reports when the wind speed, in the units indicated by iw, is 99 or more. The group, when required, shall be included immediately following the Nddff group.

15.3.5.1 00 – Indicator figure

The symbol 00 indicates that the 00fff group is included in the synoptic report.

15.3.5.2 fff – Wind speed, in units indicated by iw, of 99 units or more

When the synoptic speed is 99 kt or more, the fff of the 00fff group shall contain the actual wind speed and the ff of the Nddff group shall be coded as 99.
Examples:
An east wind of 118 kt shall be coded: N0999 00118
A south wind of 99 kt shall be coded: N1899 00099

15.3.6 Interpretation of group 1snTTT

15.3.6.1  – Numerical indicator figure

The figure 1 indicates that group 1snTTT is included in the report.

15.3.6.2 sn – Indicator of whether temperatures are positive or negative

The symbol sn indicates whether temperatures are positive or negative. It is coded as follows:

• sn = 0: temperature is 0 °C, or positive (above 0 °C)
• sn = 1: temperature is negative (below 0 °C)

15.3.6.3 TTT – Dry-bulb temperature

The symbol TTT indicates the dry-bulb temperature in tenths of a degree Celsius. Code the absolute value of the temperature for TTT as read, filling in a zero for the tens and units digit, if required. Examples are given in Table 15—10.

15.3.7 Interpretation of group 2snTdTdTd

15.3.7.1 2 – Numerical indicator figure

The figure 2 indicates that group 2snTdTdTd is included in the report.

15.3.7.2 sn – Indicator of whether temperatures are positive or negative

The symbol sn indicates whether temperatures are positive or negative. It is coded as follows:

• sn = 0: temperature is 0 °C, or positive (above 0 °C)
• sn = 1: temperature is negative (below 0 °C)

15.3.7.3 TdTdTd – Dew-point temperature

The symbol TdTdTd indicates the dew-point temperature in degrees and tenths of a degree Celsius. Code the absolute value of the dew-point for TdTdTd, filling in a zero for the tens and units digit, as required. Examples are given in Table 15 – 11.

15.3.8 Interpretation of group 3P0P0P0P0

This group shall be included in main synoptic reports only.

15.3.8.1 3 – Numerical indicator figure

The figure 3 indicates that group 3P0P0P0P0 is included in the report.

15.3.8.2 P0P0P0P0 – Air pressure at station level

Obtain the station pressure and code directly if the station pressure is less than 1000.0 hPa, omitting the decimal point.

If the station pressure is 1000.0 hPa or greater, code 3P0P0P0P0 by omitting the thousands digit and record the hundreds, tens, units, and tenths digits directly, omitting the decimal point. 

15.3.9 Interpretation of group 4PPPP

15.3.9.1 4 – Numerical indicator figure

The figure 4 indicates that group 4PPPP is included in the report.

15.3.9.2 PPPP – Air pressure at mean sea-level

The symbol PPPP indicates mean sea-level air pressure in tenths of a hectopascal. When sea-level pressure is less than 1 000 hPa, record and use all four digits. When sea-level pressure is 1 000 hPa or more, omit the thousands digit and record the hundreds, tens, units, and tenths digits directly. The decimal is always omitted.

15.3.10 Interpretation of group 5appp

This group shall be included whenever the three-hourly pressure tendency is available.

15.3.10.1 5 – Numerical indicator figure

The figure 5 indicates that group 5appp is included in the report.

15.3.10.2 a – Characteristic of the tendency

The symbol a indicates the characteristic of pressure tendency during the three-hour period preceding the time of observation. The three-hour characteristic shall be obtained from the pressure trace and coded in accordance with Table 15 – 15.

15.3.10.3 ppp – Net amount of atmospheric pressure change

The symbol ppp indicates the net amount of pressure tendency change during the three hours preceding the time of observation, expressed in tenths of a hectopascal. Obtain the three-hour tendency amount, and code directly for ppp inserting a zero in place of the tens digit if the amount is less than 10 hPa, and two zeros in the places of the tens and units digits if the amount is less than 1 hPa. Always omit the decimal point.

15.3.11 Interpretation of group 6RRRtR

This group shall always be included in main and intermediate synoptic reports, unless otherwise directed by the Regional Director General (see 15.3.3.1 on the use of the symbol iR).

15.3.11.1 6 – Numerical indicator figure

The figure 6 indicates that group 6RRRtR is included in the report.

15.3.11.2 RRR – Amount of precipitation

The symbol RRR indicates the amount of precipitation which has fallen during the period preceding the time of observation, as indicated by tR. Amounts are usually for a six-hour period at the main synoptic observation and a three-hour period at the intermediate observation. Six-hour amounts and three-hour amounts shall be obtained from an intermediate reading of the standard rain gauge (see 15.5.7.2).

Table 15 – 17 shall be used to specify code figures for RRR.

15.3.11.3 tR – Duration of period of reference

The symbol tR indicates the duration of period of reference for amount of precipitation, ending at the time of the report. Table 15 – 18 shall be used to specify code figures for tR.

15.3.12 Interpretation of group 7wwW1W2

This group shall be included only if present and/or past weather phenomena of significance are observed. The 7-group is omitted when weather of no significance is observed (when ww may be coded 00, 01, 02, or 03 and past weather code figures 0, 1 or 2 apply).

15.3.12.1 7 – Numerical indicator figure

The figure 7 indicates that group 7wwW1W2 is included in the report.

15.3.12.2 ww – Present weather

The term “present weather” refers to the atmospheric phenomena that are occurring at the time of observation, or which have occurred during the hour (60 minutes) preceding the time of observation. The atmospheric phenomena reported for present weather include precipitation (rain, drizzle, hail, etc.), obstructions to vision (fog, mist, haze, smoke, dust storm, sandstorm, drifting and blowing snow, and dust whirls), squalls, thunderstorms, lightning, and funnel clouds. Proper usage of the present weather ww codes requires a complete knowledge of “Definitions and Descriptions of Meteors” as given in the International Cloud Atlas.

Codes 00 to 49 (inclusive) of the symbol ww are used to code present weather when there is no precipitation at the station at the time of observation.

Codes 50 to 99 (inclusive) of the symbol ww are used to code present weather when precipitation is occurring at the station at the time of observation. Codes 50 to 99 are used not only to indicate the type of precipitation but also the intensity (light, moderate or heavy), and the character (continuous, intermittent or showery).

The first figure of the ww code corresponds to the ten principal categories of weather. Firstly, the decade most suitable to the general state of the weather is chosen; then, from that decade, the code figure is chosen which best describes the weather at the time of observation or during the one-hour period immediately preceding it (where specifically mentioned in the code).

When deciding on a decade or in determining the complete code figure for ww, do not take into account meteorological phenomena experienced more than one hour before the official time of observing the weather (with the exception of thunder, which may have been heard up to 75 minutes before the official time of the weather observation, see ww codes 29 and 91 to 94).

If more than one specification of the ww codes is applicable, the highest code figure is chosen, except that code 17 shall be given preference over codes 20 to 49.

Figure 15 – 1 is a graphic guide in which priority is indicated by the relative position of the block. This guide may be used to assist in the selection of codes for present weather. An abbreviated description of each of the code figures follows the chart. 

15.3.12.2.1 WMO code table 4677 – General description of present weather code figure WW

Code figures 00, 01, 02, and 03 represent phenomena of little significance. When these code figures are applicable for ww, combined with a code figure of 2 or less for past weather (W1W2), then ww is neither recorded nor transmitted, see 15.3.12.

Code figures 00, 01, 02 and 03 describe the general trend of changes in the state of the sky during the hour preceding the time of observation. The development (shown by increasing vertical extent or thickening) or dissolution (shown by decreasing vertical extent or thinning) is the most important factor that must be considered when choosing the most suitable number. The variation in sky cover is less important and should be used as the criterion when there is no general development or dissolution observable (ww = 00, 01 and 02 can each be used when the sky is clear at the time of observation). In this case, the following interpretation shall apply:

• 00: when the preceding conditions are not known
• 01: when the clouds have dissolved during the past hour
• 02: when the sky has been continuously clear during the past hour

Present weather code figures normally refer to the weather occurring at the time of observation. The following present weather codes are applicable to the one-hour period preceding the official time of observation: ww = 00, 01, 02, 03, 18, 19, 20 to 28, 30 to 35, and 40 to 47. Codes 29 and 90 to 94 apply for a period of up to 1 hr and 15 minutes preceding the official time of observation.

Although specifications for 04, 05 and 06 do not require visibility limits, smoke, haze and dust are usually associated with visibilities of 6 mi. or less. Specifications for 07 and 10 require that the visibility be restricted to 6 or less.

Code figures 20 to 29 shall never be used when precipitation is occurring at the station at the time of observation.

Code figures 80 to 90 are used only when the precipitation is showery in character and is occurring at the station at the time of observation.

The expressions “during the past hour” and “during the preceding hour” used in the ww code table refer to the full hour (60 minutes) preceding the official time at which the weather is observed for the synoptic observation.

15.3.12.2.2 WMO code table 4677—Detailed specification of present weather code figure WW

Code figure 00 shall be used when the cloud development during the preceding hour is unknown or has not been observed.

Code figure 01 shall be used when the clouds have shown a tendency to dissolve or to decrease in vertical development during the preceding hour (e.g. code figure 01 is applicable to the decrease of fine weather Cumulus late in the day).

Code figure 02 shall be used when there has been no appreciable change in the state of the sky during the preceding hour.

Code figure 03 shall be used when the clouds have shown a tendency to form or develop during the preceding hour (e.g. this figure is applicable when cumulus clouds are forming and also when fair weather Cumulus is developing into Cumulus Congestus).

Code figure 04 shall be used when the prevailing visibility is restricted by smoke (e.g. forest fire, industrial smoke or volcanic ash).

Code figure 05 shall be used when the obstruction to vision consists of lithometeors, generally known as “haze.”

Code figure 06 shall be used when the prevailing visibility is restricted by dust suspended in the air, not raised by wind.

Code figure 07 shall be used when blowing dust or blowing sand is observed at or near the station at the time of observation and the prevailing visibility is observed to be not more than 6 mi., but no well-developed dust whirl(s) or sand whirl(s) and no dust storm or sandstorm is seen.

Code figure 08 shall be used when well developed dust whirls or sand whirls are seen at or near the station during the preceding hour or at the time of observation, but no dust storm or sandstorm.

Code figure 09 shall be used when a dust storm or sandstorm is within sight at the time of observation or has occurred at the station during the preceding hour and the estimated or observed visibility in the dust storm or sandstorm is/was less than ⅝ mi.

Code figure 10 shall be used when mist (e.g. fog or freezing fog) is observed and the prevailing visibility is 6 mi. or less but not less than ⅝ mi.

Code figure 11 shall be used when patches of shallow fog or freezing fog are observed at the station at the time of observation. The depth of the fog shall not restrict visibility at eye level; however, the fog must be dense enough so that the apparent visibility in the fog is less than ⅝ mi.

Code figure 12 shall be used when more or less continuous shallow fog or freezing fog is observed at the station at the time of observation. The depth of the fog shall not restrict visibility at eye level; however, the fog must be dense enough so that the apparent visibility in the fog is less than ⅝ mi. Code figure 12 shall be used in preference to code figure 11 when shallow fog is observed to cover more than half of the ground normally visible.

Code figure 13 shall be used when lightning is seen at the time of observation or within 15 minutes preceding the time of observation, but no thunder is heard.

Code figure 14 shall be used to report Virga (i.e. precipitation within sight, but not reaching the ground or the surface of the sea).

Code figure 15 shall be used when precipitation is within sight and is reaching the ground or the surface of the sea, at an estimated distance of more than 3 mi. from the station.

Code figure 16 shall be used when precipitation is within sight and is reaching the ground or the surface of the sea, at an estimated distance of 3 mi. or less from the station, but not at the station.

Code figure 17 shall be used when thunder is heard at the time of observation, or within 15 minutes preceding the time of observation, and no precipitation is occurring at the station at the time of observation.¹

Code figure 18 shall be used when squalls occur at the time of observation, or have occurred within the preceding hour.

Code figure 19 shall be used when a funnel cloud, waterspout, or tornado is within sight of the station at the time of observation or was observed during the preceding hour. In the case of a tornado, the plain language word “TORNADO” shall be recorded and transmitted as the last group of Section 3, whether or not ww is encoded as 19.

Code figure 20 shall be used when drizzle or snow grains have occurred at the station during the preceding hour, but are not occurring at the time of observation. If freezing drizzle has occurred during the preceding hour, use code figure 24.

Code figure 21 shall be used when rain (not rain showers) has occurred at the station during the preceding hour, but is not occurring at the time of observation. If freezing rain has occurred during the preceding hour, use code figure 24.

Code figure 22 shall be used when snow (not snow showers) or ice crystals have occurred at the station during the preceding hour, but are not occurring at the time of observation.

Code figure 23 shall be used when mixed rain and snow, or ice pellets have occurred at the station during the preceding hour but are not occurring at the time of observation.

Code figure 24 shall be used when freezing rain (non-showery) or freezing drizzle has occurred at the station during the preceding hour, but is not occurring at the time of observation.

Code figure 25 shall be used when a rain shower has occurred at the station during the preceding hour, but is not occurring at the time of observation.

Code figure 26 shall be used when a snow shower or a shower of rain and snow has occurred at the station during the preceding hour, but is not occurring at the time of observation.

Code figure 27 shall be used when a shower of hail, or of hail and rain, has occurred at the station during the preceding hour, but is not occurring at the time of observation. For purposes of reporting code figure 27, hail may be considered to mean any one, or any combination of hail or, snow pellets.

Code figure 28 shall be used when fog or freezing fog, with visibility less than ⅝ mi. has occurred at the station during the preceding hour, but is not occurring at the time of observation.

Code figure 29 shall be used when a thunderstorm with or without precipitation, has occurred at the station during the preceding hour, but neither thunder nor precipitation is occurring at the time of observation. This requires that the last thunder be heard 15 minutes or more before the time of observation. For purposes of reporting this code figure, the “preceding hour” is from 1 hour and 15 minutes ago to 15 minutes ago.

Code figure 30 shall be used when a dust storm or sandstorm is occurring at the station at the time of observation, the intensity of the phenomenon has decreased during the past hour, and the visibility is less than ⅝ mi. but not less than 5/16 mi.³

Code figure 31 shall be used when a dust storm or sandstorm is occurring at the station at the time of observation, the intensity has shown no appreciable change during the past hour, and the visibility is less than ⅝ mi. but not less than 5/16 mi.³

Code figure 32 shall be used when a dust storm or sandstorm is occurring at the station at the time of observation, the phenomenon has begun or increased in intensity during the past hour, and the visibility is less than ⅝ mi. but not less than 5/16 mi.³

Code figure 33 shall be used when a dust storm or sandstorm is occurring at the station at the time of observation, the intensity of the phenomenon has decreased during the past hour, and the visibility is less than 5/16 mi.³

Code figure 34 shall be used when a dust storm or sandstorm is occurring at the station at the time of observation, the intensity has shown no appreciable change during the past hour, and the visibility is less than 5/16 mi.³

Code figure 35 shall be used when a dust storm or sandstorm is occurring at the station at the time of observation, the phenomenon has begun or increased in intensity during the past hour, and the visibility is less than 5/16 mi.³

Code figure 36 shall be used when drifting snow of light or moderate intensity is occurring at the station at the time of observation.²

Code figure 37 shall be used when heavy drifting snow is occurring at the station at the time of observation.²

Code figure 38 shall be used when blowing snow is occurring at the station at the time of observation, and the visibility is 5/16 mi. or more.³

Code figure 39 shall be used when blowing snow is occurring at the station at the time of observation, and the visibility is less than 5/16 mi. ³

Code figure 40 shall be used when a bank of fog or freezing fog estimated to be more than 2 m in depth is observed at a distance from the station at the time of observation but not at the station during the preceding hour. The observer must estimate that the visibility appears to be restricted in the fog to less than 5/8 mi. to justify the use of ww = 40.

Code figure 41 shall be used when fog or freezing fog, more than 2 m deep, is occurring in patches at the time of observation, and the prevailing visibility is restricted to less than ⅝ mi.

Code figure 42 shall be used when fog or freezing fog is occurring at the station at the time of observation, the visibility is less than ⅝ mi., the sky is visible, and the fog has become thinner during the past hour.

Code figure 43 shall be used when fog or freezing fog is occurring at the station at the time of observation, the visibility is less than ⅝ mi., the sky is not visible, and the fog has become thinner during the past hour.

Code figure 44 shall be used when fog or freezing fog is occurring at the station at the time of observation, the visibility is less than ⅝ mi., the sky is visible, and the fog has shown no appreciable change in intensity during the past hour.

Code figure 45 shall be used when fog or freezing fog is occurring at the station at the time of observation, the visibility is less than ⅝ mi., the sky is not visible, and the fog has shown no appreciable change in intensity during the past hour.

Code figure 46 shall be used when fog or freezing fog is occurring at the station at the time of observation, the visibility is less than ⅝ mi., the sky is visible, and the fog has begun or become thicker during the past hour.

Code figure 47 shall be used when fog or freezing fog is occurring at the station at the time of observation, the visibility is less than ⅝ mi., the sky is not visible, and the fog has begun or become thicker during the past hour.

Code figure 48 shall be used when fog is occurring at the station at the time of observation, the visibility is less than ⅝ mi., the sky is visible, and the fog is depositing rime.

Code figure 49 shall be used when fog is occurring at the station at the time of observation, the visibility is less than ⅝ mi., the sky is not visible, and the fog is depositing rime.

Code figure 50 or 51 shall be used when slight drizzle is occurring at the station at the time of observation:

• code figure 50 shall be used when the drizzle is intermittent
• code figure 51 shall be used when the drizzle is continuous

Code figure 52 or 53 shall be used when moderate drizzle is occurring at the station at the time of observation:

• code figure 52 shall be used when the drizzle is intermittent
• code figure 53 shall be used when the drizzle is continuous

Code figure 54 or 55 shall be used when heavy drizzle is occurring at the station at the time of observation:

• code figure 54 shall be used when the drizzle is intermittent
• code figure 55 shall be used when the drizzle is continuous

Code figure 56 or 57 shall be used when freezing drizzle is occurring at the station at the time of observation:

• code figure 56 shall be used when the freezing drizzle is slight
• code figure 57 shall be used when the freezing drizzle is moderate or heavy

Code figure 58 shall be used when drizzle and rain are occurring together at the station at the time of observation, and both types of precipitation are of slight intensity.

Code figure 59 shall be used when drizzle and rain are occurring together at the station at the time of observation, and either the rain, or the drizzle, or both, are of moderate or heavy intensity.

Code figure 60 or 61 shall be used when slight rain is occurring at the station at the time of observation:

• code figure 60 shall be used when the rain is intermittent
• code figure 61 shall be used when the rain is continuous

Code figure 62 or 63 shall be used when moderate rain is occurring at the station at the time of observation:

• code figure 62 shall be used when the rain is intermittent
• code figure 63 shall be used when the rain is continuous

Code figure 64 or 65 shall be used when heavy rain is occurring at the station at the time of observation:

• code figure 64 shall be used when the rain is intermittent
• code figure 65 shall be used when the rain is continuous

Code figure 66 or 67 shall be used when freezing rain is occurring at the station at the time of observation:

• code figure 66 shall be used when the freezing rain is slight
• code figure 67 shall be used when the freezing rain is moderate or heavy

Code figure 68 shall be used when snow, accompanied by drizzle or freezing drizzle, or by rain or freezing rain, is occurring at the station at the time of observation and each of the precipitation types is of slight intensity.⁴

Code figure 69 shall be used when snow, accompanied by drizzle or freezing drizzle, or by rain or freezing rain, is occurring at the station at the time of observation and at least one of the precipitation types is of moderate or heavy intensity.⁴

Code figure 70 or 71 shall be used when slight snow, in flakes, is occurring at the station at the time of observation:

• code figure 70 shall be used when the snow is intermittent
• code figure 71 shall be used when the snow is continuous

Code figure 72 or 73 shall be used when moderate snow, in flakes, is occurring at the station at the time of observation:

• code figure 72 shall be used when the snow is intermittent
• code figure 73 shall be used when the snow is continuous

Code figure 74 or 75 shall be used when heavy snow, in flakes, is occurring at the station at the time of observation:

• code figure 74, when the snow is intermittent
• code figure 75, when the snow is continuous

Code figure 76 shall be used when ice crystals (diamond dust) are occurring at the station at the time of observation, whether or not fog or freezing fog is present at the same time.

Code figure 77 shall be used when snow grains are occurring at the station at the time of observation, whether or not fog or freezing fog is present at the same time.

Code figure 78 shall be used when isolated star-like snow crystals are occurring at the station at the time of observation, whether or not fog or freezing fog is present at the same time.

Code figure 79 shall be used when ice pellets are occurring at the station at the time of observation.

Code figure 80 shall be used when slight rain showers are occurring at the station at the time of observation.

Code figure 81 shall be used when moderate or heavy rain showers are occurring at the station at the time of observation.

Code figure 82 shall be used when exceptionally heavy or torrential rain showers are occurring at the station at the time of observation.⁵

Code figure 83 shall be used when showers of mixed rain and snow are occurring at the station at the time of observation, and both types are slight.

Code figure 84 shall be used when showers of mixed rain and snow are occurring at the station at the time of observation, and either one or both of the precipitation types are moderate or heavy.

Code figure 85 shall be used when showers of slight snow are occurring at the station at the time of observation.

Code figure 86 shall be used when showers of moderate or heavy snow are occurring at the station at the time of observation.

Code figure 87 shall be used when showers of slight snow pellets or small hail, with or without rain, or rain and snow mixed, are occurring at the station at the time of observation.

Code figure 88 shall be used when moderate or heavy showers of snow pellets or small hail, with or without rain, or rain and snow mixed, are occurring at the station at the time of observation.

Code figure 89 shall be used when showers of slight hail, with or without rain, or rain and snow mixed, not accompanied by thunder, are occurring at the station at the time of observation.

Code figure 90 shall be used when showers of moderate or heavy hail, with or without rain, or rain and snow mixed, not accompanied by thunder, are occurring at the station at the time of observation.

Thunderstorm during past hour, but not at time of observation

Code figure 91 shall be used when slight rain is occurring at the station at the time of observation, and a thunderstorm has occurred during the preceding hour, but is not occurring at the time of observation.⁶

Code figure 92 shall be used when moderate or heavy rain is occurring at the station at the time of observation, and a thunderstorm has occurred during the preceding hour, but is not occurring at the time of observation.⁶

Code figure 93 shall be used when snow, or rain and snow mixed, or hail, or snow pellets are occurring at the station at the time of observation, and a thunderstorm has occurred during the preceding hour, but is not occurring at the time of observation. This code figure shall be used when the precipitation type or types are of slight intensity.⁶

Code figure 94 shall be used when snow, or rain and snow mixed, or hail, or snow pellets are occurring at the station at the time of observation, and a thunderstorm has occurred during the preceding hour, but is not occurring at the time of observation. This code figure shall be used when one or more of the precipitation types are of moderate or heavy intensity.⁶

Thunderstorm in progress at time of observation

Code figure 95 shall be used when a thunderstorm accompanied by rain or snow is occurring at the station at the time of observation.^{7, 8}

Code figure 96 shall be used when a thunderstorm accompanied by hail, snow pellets is occurring at the station at the time of observation. Rain or snow may occur along with the hail, etc.⁷

Code figure 97 is no longer used in Canada.

Code figure 98 shall be used when a thunderstorm, accompanied by a dust storm or sandstorm, is occurring at the station at the time of observation (precipitation occurring). Under these circumstances, the precipitation may not be visible, and the observer must judge whether precipitation is actually occurring.^{7, 8}

Code figure 99 is no longer used in Canada.

15.3.12.3 W1W2 – Past weather

The symbol W1W2 indicates the past weather at the station and duration of weather and obstructions to vision as well as other items of previous observations. Two types of past weather may be selected. The highest applicable code figure is assigned to W1 and the second highest to W2. Table 15 – 19 shall be used to specify code figures for W1W2.

15.3.12.3.1 Period covered by W1W2

The period covered by W1W2 normally begins at the actual time of observation of the previous synoptic report and ends at the time the present weather (ww) began and so will cover a maximum of 6 hr for main synoptics.

15.3.12.3.2 Break in weather during period covered by W1W2

If during the period covered by W1W2 there has been a break in the weather watch exceeding 30 minutes which, in the considered opinion of the observer, makes a reasonable assessment of past weather impossible, W1W2 may be recorded as XX.

15.3.12.3.3 Requirement to give a complete description

The code figures for W1 and W2 shall be selected in such a way that W1W2 and ww together give as complete a description as possible of the weather in the time interval concerned, based on their significance according to WMO code tables 4677 and 4561.

15.3.12.3.4 Using W1W2 and ww together to give a complete description

The standard for using W1W2 and ww to give a complete description of the present and past weather is as follows:

1. If the type of weather undergoes a complete change during the time interval concerned, the code figures selected for W1 and W2 shall describe the weather prevailing before the type of weather indicated by ww began.
2. If only one type of weather has been occurring throughout the whole period, use that one type for ww, W1, and W2.
3. If more than one type of weather has been occurring throughout the whole period, after selecting ww, select the most significant type of past weather
   1. ensure that the selection for W1 is different from ww, though they may be occurring simultaneously
4. After selecting the first past weather type, select another past weather type for W2 that is different, if possible, from the first past weather type (W1) that has occurred during the past weather period
   1. if more than one code figure may be given to past weather, the highest figure shall be reported for W1 and the second highest applicable code figure shall be reported for W2
   2. if only one type of past weather has occurred during the past weather period, encode W1 and W2 the same

15.3.12.3.5 Examples of how to code for 7wwW1W2

The 7-group gives a qualitative rather than quantitative picture of the weather during the past weather period. It generally does not give the sequence or duration of weather events, unless ww, W1 and W2 are all coded the same, in which case only one type of weather has prevailed throughout the period.

The following examples, shown graphically, of weather conditions during a “past weather” period of six hours illustrate how the rules are applied when coding W1 and W2. The proper coding of ww and W1 and W2 is given for each example. These examples, where appropriate, also illustrate the coding of the special phenomena group 909Rtdc in Section 3 of the synoptic code (see 15.5.9.3).

Users of the 7–group code should be aware that decoding ambiguities are possible. In examples 5 and 6 below, different weather sequences give rise to similar code sequences. Note how W1 in these examples differs with respect to duration of the snow and rain.

 

15.3.13 Interpretation of group 8NhCLCMCH

This group shall be omitted when the sky is clear (N = 0), or when the sky is totally obscured (N = 9) and no cloud is visible below the obscuration.

The observer must keep in mind that the analysis of sky condition by layers and individual cloud types is not always directly applicable to coding the clouds in this group of the synoptic code. For example, when coding clouds in the CL category, if CB is present in any amount, the coding must be 3 or 9 (see 15.3.13.3.1). Similarly, when coding clouds in the CM category, if turreted or tufted Altocumulus is present it must be reported using code figure 8 (unless code 9 applies) even though another type of Altocumulus or Altostratus covers a greater portion of the celestial dome (see 15.3.13.4.1). In the 8-group, three categories of clouds can be coded along with the amount of one category.

15.3.13.1 8 – Numerical indicator figure

The figure 8 indicates that group 8NhCLCMCH is included in the report.

15.3.13.2 Nh – Amount of cloud

The symbol Nh indicates the amount of cloud. The amount coded for Nh shall be the total amount of all cloud in the CL category, or in the absence of CL cloud, it shall be the total amount of all cloud in the CM category. If CH clouds alone are present, Nh shall be coded as 0. Table 15—6 shall be used to specify code figures for Nh.

15.3.13.2.1 Obscuring phenomena

When blue sky or stars are seen through a layer of fog or other obscuring phenomena, without any trace of cloud above or within this layer, the group 8NhCLCMCH shall be omitted. If clouds are seen through the fog or other obscuring phenomena, their amount shall be evaluated as though the obscuration did not exist. In other words, partial obscuration is not considered and Nh is evaluated in terms of the visible portion of the sky. Table 15 – 7 may be helpful in determining Nh under partially obscured conditions.

15.3.13.2.2 Sky is completely obscured

If the sky is completely obscured, and no cloud is visible, the group 8NhCLCMCH shall be omitted. If the sky is completely obscured and clouds are visible below the obscuration or below the extent of vertical visibility in the obscuration, Nh is reported as observed. For example, if the sky is completely obscured and ⅛ okta of Stratus Fractus is observed, the cloud elements would be recorded as N = 9, Nh = 1, CL= 7 and both CM and CH = X, unless the obscuration is a layer aloft based above the middle cloud level, in which case CM = 0.

15.3.13.2.3 Height restrictions

In the coding of Nh, there are no height restrictions for clouds of the CL or CM categories (i.e., convective type clouds, CU, TCU or CB which based at 12 000 ft (3 600 m) would be reported as cloud of the CL category and would be added to all CL clouds present).

15.3.13.2.4 Condensation trails

Persistent condensation trails and cloud masses that have obviously developed from condensation trails shall be reported as cloud, using the appropriate CH or CM code figure. Rapidly dissipating condensation trails shall not be reported.

15.3.13.2.5 Mackerel sky

With a mackerel sky (AC or SC perlucidus), breaks between the cloud elements always exist. Hence, even when such a layer extends over the whole celestial dome, Nh shall be coded as 7 or less.

15.3.13.3 CL – Low cloud types

The symbol CL indicates the type of low cloud present of the genera stratocumulus, stratus, cumulus and cumulonimbus. Code figures for CL are given in Table 15 – 20 followed by the corresponding specification.

15.3.13.3.1 Priority of reporting for CL clouds

Two or more types of low cloud are often present in the sky at the same time. To assist the observer in this situation, the following ordered list showing the priority of code figures for CL has been developed. If two or more code figures are applicable, go down the following list and report the first figure that is applicable, no matter how small the amount of this type may be, and regardless of the presence of other types having a lower priority.

Ordered list showing the priority of code figures for CL and coding criteria:

1. If Cumulonimbus is present, with or without other CL-clouds, then:
   1. CL = 9 if the upper part of at least one of the Cumulonimbus clouds is clearly fibrous or striated1
   2. CL = 3 if the upper part of none of the Cumulonimbus clouds is clearly fibrous or striated
2. If there is no Cumulonimbus present, then:
   1. CL = 4 if Stratocumulus formed by the spreading out of Cumulus is present
   2. CL = 8 if the CL code figure 4 is not applicable and if Cumulus and Stratocumulus clouds with bases at different levels are present
   3. CL = 2 if the CL code figures 4 and 8 are not applicable and if Cumulus clouds of moderate or strong vertical extent are present
   4. if the CL code figures 4, 8 and 2 are not applicable:
      1. CL = 1 if the CL clouds present are predominantly2 Cumulus with little vertical extent and seemingly flattened or ragged Cumulus other than of bad weather, or both
      2. CL = 5 if among the CL clouds present, Stratocumulus other than that formed by the spreading out of Cumulus is predominant2
      3. CL = 6 if the CL clouds present are predominantly2 Stratus in a more or less continuous sheet or layer, or in ragged shreds (other than ragged Stratus of bad weather), or both
      4. CL = 7 if the CL clouds present are predominantly2 pannus (ragged shreds of Stratus of bad weather3 or ragged Cumulus of bad weather, or both)
3. CL = 0 if there is no Stratocumulus, Stratus, Cumulus or Cumulonimbus
4. CL = / (use “ / ” only under conditions outlined in Table 15—20)

15.3.13.4 CM – Middle cloud types

The symbol CM indicates the type of middle cloud present of the genera Altocumulus, Altostratus, and Nimbostratus. Code figures for CM are given in Table 15 – 21 followed by the corresponding specification.

15.3.13.4.1 Priority of reporting for CM clouds

Two or more types of middle cloud are often present in the sky at the same time. To assist the observer in this situation, the following ordered list showing the priority of code figures for CM has been developed. If two or more code figures are applicable, go down the following list and report the first figure that is applicable, no matter how small the amount of this type may be, and regardless of the presence of other types having a lower priority.

Ordered list showing the priority of code figures for CM and coding criteria:

1. If Altocumulus is present (Altostratus or Nimbostratus may be present), then:
   1. CM = 9 if the sky is chaotic
   2. CM = 8 if the CM code figure 9 is not applicable and if Altocumulus with sproutings in the form of turrets or battlements or Altocumulus having the appearance of small cumuliform tufts is present
   3. CM = 7 if the CM code figures 9 and 8 are not applicable and if Altostratus or Nimbostratus is present together with Altocumulus
2. If Altocumulus is present (no Altostratus or Nimbostratus present), then:
   1. CM = 6 if the CM code figures 9, 8 and 7 are not applicable and if Altocumulus formed by the spreading out of Cumulus or Cumulonimbus is present
   2. CM = 5 if the CM code figures 9, 8, 7 and 6 are not applicable, and if the Altocumulus present is progressively invading the sky
   3. CM = 4 if the CM code figures 9, 8, 7, 6 and 5 are not applicable and if the Altocumulus present is continually changing in appearance
   4. CM = 7 if the CM code figures 9, 8, 6, 5 and 4 are not applicable and if the Altocumulus present occurs at two or more levels
   5. CM = 7 or 3 if the CM code figures 9, 8, 6, 5 and 4 are not applicable and if the Altocumulus present occurs at one level, use CM = 7 or 3 depending on whether the greater part of the Altocumulus is respectively opaque or semi‑transparent
3. If no Altocumulus is present:
   1. CM = 2 if Nimbostratus is present or if the greater part of the Altostratus present is opaque
   2. CM = 1 if there is no Nimbostratus and if the greater part of the Altostratus present is semi-transparent
4. CM = / if CM clouds invisible owing to continuous layer of lower clouds or because of fog, blowing dust or other similar phenomena (use only under the conditions given in Table 15—21 )
5. CM = 0 if there is no Altocumulus, Altostratus or Nimbostratus

15.3.13.5 CH – High cloud types

The symbol CH indicates the type of high cloud present of genera Cirrus, Cirrocumulus and Cirrostratus. Code figures for CH are given in Table 15 – 22 followed by the corresponding specification.

15.3.13.5.1 Priority of reporting for CH clouds

Two or more types of high cloud are often present in the sky at the same time. To assist the observer in this situation, the following ordered list showing the priority of code figures for CH has been developed. If two or more code figures are applicable, go down the following list and report the first figure that is applicable, no matter how small the amount of this type may be, and regardless of the presence of other types having a lower priority.

Ordered list showing the priority of code figures for CH and coding criteria:

1. CH = 9 if Cirrocumulus is present alone or if the amount of the Cirrocumulus is more than the combined sky cover of any Cirrus and Cirrostratus present
   1. if CH = 9 is not applicable and Cirrostratus present with or without Cirrus or Cirrocumulus, then:
      1. CH = 7 if the Cirrostratus covers the whole sky
      2. CH = 8 if the Cirrostratus does not cover the whole sky and is not invading the celestial dome
      3. CH = 6 if the Cirrostratus is progressively invading the sky and if the continuous veil extends more than 45° above the horizon but does not cover the whole sky
      4. CH = 5 if the Cirrostratus is progressively invading the sky but the continuous veil does not reach 45° above the horizon
   2. if CH = 9 is not applicable and no Cirrostratus present, then:
      1. CH = 4 if the Cirrus clouds are invading the sky
      2. CH = 3 if the CH code figure 4 is not applicable and if dense Cirrus which originated from Cumulonimbus is present in the sky
      3. if CH = 4 or 3 are not applicable:
         1. CH = 2 if the combined sky cover of dense Cirrus, of Cirrus with sproutings in the form of small turrets or battlements and of Cirrus in tufts is greater than the combined sky cover of Cirrus in the form of filaments, strands or hooks
         2. CH = 1 if the combined sky cover of Cirrus in the form of filaments, strands or hooks is greater than the combined sky cover of dense Cirrus, of Cirrus with sproutings in the form of small turrets or battlements and of cirrus in tufts
2. CH = / if CH clouds invisible owing to continuous layer of lower clouds or because of fog, blowing dust or other similar phenomena (code / only under the conditions given in Table 15 – 22)
3. CH = 0 if there is no Cirrus, Cirrostratus or Cirrocumulus

15.3.14 Interpretation of group 9GGgg

15.3.14.1 9 – Numerical indicator figure

The figure 9 indicates that group 9GGgg is included in the report.

15.3.14.2 GGgg – Actual time of observation if different than GG

The symbols GGgg indicate the actual time of observation at a data platform when this time differs from the scheduled synoptic hour UTC. This group shall be included when the actual time of observation differs by more than 10 minutes from the standard time GG reported in Section 0 (see 15.2.4.2).

15.4 Section 2 – Reporting data for sea stations

Section 2 contains maritime data pertaining to sea stations. Standards and procedures for Section 2 of the Synoptic code may be found in Manual of Marine Weather Observations (MANMAR).

15.5 Section 3 – Reporting data for regional and national exchange

Section 3 contains data for regional and national exchange only. It is always included in reports from Canadian land stations.

15.5.1 Symbolic form

333 1snTxTxTx 2snTnTnTn 4E’sss 6RRRtR 7R24R24R24R24 9SPSPspsp

15.5.2 Section content

Standards for inclusion of reported groups in Section 3 are as follows:

1. In the main synoptic report, the indicator group 333 and groups 1snTxTxTx, 2snTnTnTn and 7R24R24R24R24 shall always be included
2. Group 4E’sss is included when there is snow or ice on the ground
3. Group 9SPSPspsp shall be included if precipitation has occurred
4. Group 9SPSPspsp is included if there are special phenomena to report

15.5.3 333 – Numerical indicator figure group

The three-figure group 333 indicates the beginning of Section 3. This three-figure group must precede the code groups of Section 3 which follow.

15.5.4 Interpretation of group 1snTxTxTx

15.5.4.1 1 – Numerical indicator figure

The figure 1 indicates that the group 1snTxTxTx is included in the report.

15.5.4.2 sn – Indicator of whether temperatures are positive or negative

The symbol sn is used to indicate whether the temperature given by TxTxTx is positive or negative. It shall be coded as follows:

• sn = 0 if the temperature is 0 °C, or positive (above 0 °C)
• sn = 1 if the temperature is negative (below 0 °C)

15.5.4.3 TxTxTx – Maximum temperature

The symbols TxTxTx indicate the maximum temperature, in degrees and tenths of a degree Celsius. This group shall always be reported. Maximum temperature shall be reported according to the following schedule:

• at 1200 UTC, report the maximum temperature for the 24-hour period ending 6 hours ago, i.e. 0600 UTC
• at 1800 UTC and 0000 UTC, report the maximum temperature for the previous 12 hours
• at 0600 UTC, report the maximum temperature for the previous 24 hours (this is the same maximum temperature reported 6 hours later in the 1200 UTC synoptic report)

Table 15—23 shows examples of maximum temperature coded for 1snTxTxTx.

15.5.5 Interpretation of group 2snTnTnTn

15.5.5.1 2 – Numerical indicator figure

The figure 2 indicates that group 2snTnTnTn is included in the report.

15.5.5.2 sn – Indicator of whether temperatures are positive or negative

The symbol sn indicates whether the temperature given by TnTnTn is positive or negative. It shall be coded as follows:

• sn = 0 if the temperature is 0 °C or positive (above 0 °C)
• sn = 1 if the temperature is negative (below 0 °C)

15.5.5.3 TnTnTn – Minimum temperature

The symbols TnTnTn indicate the minimum temperature in degrees and tenths of a degree Celsius. The examples shown in Table 15 – 23 also apply to minimum temperature. This group shall always be reported. Minimum temperature shall be reported according to the following schedule:

• at 1200 UTC, report the minimum temperature for the previous 12 hours
• at 1800 UTC and 0600 UTC, report the minimum temperature for the previous 24 hours
• at 0000 UTC, report the minimum temperature for the previous 18 hours

15.5.6 Interpretation of group 4E’sss

This group shall be included in each main synoptic report when there is snow, ice, or any other form of solid precipitation such as hail, ice pellets, or snow pellets on the ground at the time of the observation and precipitation has occurred since the previous main synoptic observation.

Group 4E’sss shall also be included in the 1200 UTC observation whenever there is solid precipitation on the ground at the time of observation, regardless of when it occurred. If the 1200 UTC synoptic observation is not taken, the group is included in the next main synoptic observation.

15.5.6.1 4 – Numerical indicator figure

The figure 4 indicates that group 4E’sss is included in the report.

15.5.6.2 E’ – State of the ground with snow or measurable ice

The symbol E’ indicates the state of the ground with snow or measurable ice cover. Table 15 – 24 shall be used to specify code figures for E’ conforming to the following criteria:

• the highest applicable code figure is always reported
• the definitions in the table apply to an open, representative area
• the term “ice,” as used in the table, also includes solid precipitation other than snow

15.5.6.3 sss – Total depth of snow or ice

The symbol group sss indicates the total depth of snow, or ice, on the ground, in whole centimetres. The depth of snow shall be coded according to Table 15 – 25.

15.5.7 Interpretation of group 6RRRtR

This group shall be included in intermediate synoptic reports at stations that normally measure precipitation (see 15.3.3.1 on the use of the symbol iR).

15.5.7.1 6 – Numerical indicator figure

The figure 6 indicates that the group 6RRRtR is included in the report. This group is included in Section 3 only in intermediate synoptic reports.

15.5.7.2 RRR – Amount of precipitation

The symbol RRR indicates the amount of precipitation which has fallen during the period preceding the time of observation (which is indicated by tR). Amounts are usually for a three-hour period at the intermediate observation. Precipitation amounts should be obtained from an intermediate reading of the standard rain gauge, without emptying its contents. In cold weather, if the contents of the gauge are frozen, it may be necessary to replace the funnel and graduate with a spare, and measure the amount. Precipitation amounts shall be coded according to Table 15 – 17: WMO code table 3590 – Specification of code figures for RRR .

15.5.7.3 tR – Period of observation

The symbol tR indicates the duration of the period of reference ending at the time of the report for the amount of precipitation. Table 15 – 26 shall be used to specify code figures for tR.

15.5.8 Interpretation of group 7R24R24R24R24

This group shall be included in each main synoptic observation to report total amount of measurable precipitation during the preceding 24 hours.

15.5.8.1 7 – Numerical indicator figure

The figure 7 indicates that group 7R24R24R24R24 is included in the report.

15.5.8.2 R24R24R24R24 – Total amount of precipitation during the 24-hour period

The symbol R24R24R24R24 indicates the total amount of precipitation during the 24-hour period ending at the time of observation. The amount shall be coded in tenths of millimetres. Table 15 – 27 provides examples of how to code for R24R24R24R24.

15.5.9 Interpretation of group 9SPSPspsp

This group is used to give supplementary information on special phenomena. Although the codes provide for the reporting of various special phenomena, unless special instructions are received from the ADM, only two 9–groups shall be used:

1. 909Rtdc: This special phenomena group shall be used indicate the time at which precipitation began or ended and duration and character of precipitation, and:
   1. this information shall be reported using the group 909Rtdc whenever group 6RRRtR is encoded and the RRR value of this group is not coded as 000
   2. the symbol Rt shall be encoded in accordance with Table 15 – 28 and the symbol dc shall be encoded according to Table 15 – 30
2. 931ss: This special phenomena group shall be used indicate the depth of newly fallen snow (the depth of newly fallen snow is the amount of snow that would have accumulated, had it not been disturbed by the wind or melted–it is essentially the rounded value of the amount recorded), and:
   1. the measurement is reported in the group 931ss, where ss is the measurement in whole centimetres, up to 55 cm
   2. measurements above 55 cm shall be encoded in accordance with Table 15 – 31
   3. the group shall be included at the discretion of the Regional Director General, but only by stations that take four staffed synoptic observations daily and when the rounded measurement is 1 cm or more

15.5.9.1 9 – Numerical indicator figure

The figure 9 indicates that group 9SPSPspsp is included in the report.

15.5.9.2 SPSP – Supplementary information group indicator

The symbol SPSP indicates which supplementary information group is included in the report.

Table 15 – 28 shall be used to specify code figures for SPSP.

15.5.9.3 Group 909Rtdc – Supplemental precipitation information

15.5.9.3.1 Rt – Time at which precipitation began or ended

The symbol Rt indicates the time at which precipitation given by RRR began or ended. Rt shall be coded with reference to the official time of observation. When precipitation is occurring at the time of observation, Rt shall refer to the “time precipitation began.” When precipitation is not occurring at the time of observation, Rt shall refer to the “time precipitation ended,” except:

1. if the coding of ww indicates that precipitation has ended during the preceding hour (ww codes 20 to 27 and 29), Rt shall be coded to indicate the “time precipitation began”
2. when two or more periods of precipitation occur during a six–hour period preceding the observation, then the time (beginning or ending) of the last period of precipitation shall be reported using Rt (occurrences of precipitation shall be considered as separate periods of precipitation when separated by 15 minutes or more)

Table 15 – 29 shall be used to specify code figures for Rt.

15.5.9.3.2 dc – Duration and character of precipitation

The symbol dc indicates the duration and character of precipitation given by RRR. Occurrences of precipitation shall be considered as separate periods of precipitation when separated by intervals of 15 minutes or more. Table 15 – 30 shall be used to specify code figures for dc.

15.5.9.4 Group 931ss

15.5.9.4.1 ss — Depth of newly fallen snow

The symbol ss indicates the depth of newly fallen snow. Table 15 – 31 shall be used to specify code figures for ss.

15.6 Section 4 – Data for national use for clouds with base below station level, included by national decision

Section 4 is not used in Canada.

15.7 Section 5 – Reporting data for national exchange

Section 5 is used by land stations to transmit data for national exchange only.

15.7.1 Symbolic form

555 1ssss 2swswswsw 3dmdmfmfm 4fhftftfi

15.7.2 Section content

The groups in this section pertain to summarized daily climatological data and distribution is within Canada only. Standards for inclusion of Section 5 are as follows:

1. Data of Section 5 shall be reported once daily as the last section of the 0600 UTC synoptic message by all stations
2. If Section 5 data are not normally available, the group is omitted
3. At stations where the data for Section 5 are available at 1200 UTC, but not at 0600 UTC, reports including Section 5 should be reported at 1200 UTC
4. The data shall always pertain to the same 24-hour period ending at the most recent 0600 UTC time

15.7.3 555 – Numerical indicator figure group

The three-figure group 555 indicates the beginning of Section 5. This figure group must always precede the code groups of Section 5.

15.7.4 Interpretation of group 1ssss

15.7.4.1 1 – Numerical indicator figure

The figure 1 indicates that group 1ssss is included in the report.

15.7.4.2 ssss – Amount of snowfall

The symbol ssss indicates the amount of snowfall, in tenths of a centimetre, for the 24-hour period ending at 0600 UTC. Amount of snowfall shall be reported as follows:

1. The amount of the snowfall reported shall be the total amount recorded, omitting the decimal
2. A "trace" shall be encoded as 19999
3. If there has been no snowfall in the 24-hour period, the group shall be coded 10000
4. If snowfall could not be measured, the group shall be coded as 1////

Examples of how to code amount of snowfall for ssss are given in Table 15 – 32.

15.7.5 Interpretation of group 2swswswsw

15.7.5.1 2 – Numerical indicator figure

The figure 2 indicates that group 2swswswsw is included in the report.

15.7.5.2 swswswsw – Amount of water equivalent of snowfall

The symbol swswswsw indicates the amount of water equivalent, in tenths of a millimetre, of the 24–hour snowfall ending at 0600 UTC. Amount of water equivalent shall be reported as follows:

1. The amount of the water equivalent shall be the total amount recorded, omitting the decimal
2. A "trace" shall be coded as 29999
3. If there has been no snowfall in the 24-hour period, the group shall be coded as 20000
4. If snowfall water equivalent could not be measured, the group shall be coded as 2////

Examples of how to code the amount of water equivalent of snowfall for swswswsw are given in Table 15 – 33 .

15.7.6 Interpretation of group 3dmdmfmfm

The group is reported only when fmfm exceeds 16 kt. If a station has no serviceable wind speed detector for any period during the climatological day, data must be reported as missing, and the group shall be recorded as 3xxxx. A case where wind direction is missing, but wind speed is available would be recorded as 3xxfmfm.

15.7.6.1 3 – Numerical indicator figure

The figure 3 indicates that the group 3dmdmfmfm is included in the report.

15.7.6.2 dmdm – Direction of the maximum wind

The symbol dmdm indicates the direction, in tens of degrees, of the maximum wind for the 24–hour period ending at 0600 UTC. The direction encoded is the direction associated with the maximum wind speed for the period.

15.7.6.3 fmfm – Maximum wind speed for 24-hour period

The symbol fmfm indicates the maximum wind speed, in knots, for the 24-hour period ending at 0600 UTC. The speed may be either a mean or gust speed, but fmfm is encoded only when the maximum speed for the period exceeds 16 kt. The units and tens values recorded shall be the value encoded for fmfm.

15.7.7 Interpretation of group 4fhftftfi

This group is reported whenever group 3dmdmfmfm is reported. At stations equipped to record entries, or at stations where there has been a period of wind equipment unserviceability, the group 4fhftftfi shall be reported only when fi can be coded as a 2 or 3 (i.e., recorded in the format 4xxxfi).

15.7.7.1 4 – Numerical indicator figure

The figure 4 indicates that group 4fhftftfi is included in the report.

15.7.7.2 fh – Hundreds digit of the maximum wind speed

The symbol fh indicates the hundreds digit of the maximum wind speed for the 24–hour period ending at 0600 UTC. Normally fh is encoded 0; however, if, for example, a gust of 108 kt was observed, fh would be encoded 1.

15.7.7.3 ftft – Time of occurrence of maximum wind speed

The symbol ftft indicates the time of occurrence, UTC, of the maximum wind speed reported by group 3dmdmfmfm. The time encoded shall be derived from the time of the last occurrence.

15.7.7.4 fi – Speed range of the maximum wind speed

The symbol fi indicates the index value that is used to identify the speed range of the maximum two–minute mean wind speed for the 24–hour period ending at 0600 UTC. Table 15 – 34 shall be used to specify code figures for fi.

Appendix 1 Stations where SPECI reports are required for temperature changes

This appendix contains a list of NAV CANADA designated sites that are required to issue special (SPECI) reports when temperature changes occur. In accordance with ICAO (International Civil Aviation Organization) Annex 3, Appendix 3, Section 2.3, designated sites are required to issue SPECI reports when temperature changes occur that are of concern to aviation operations. Designated sites include the following airports:

• Calgary Intl., AB
• Edmonton Intl., AB
• Gander Intl., NL
• Moncton, Greater Moncton Intl., NB
• Montréal, Pierre Elliot Trudeau Intl., QC
• Montréal Intl, Mirabel, QC
• Ottawa, Macdonald-Cartier Intl., ON
• St. John's Intl., NL
• Toronto, Lester B. Pearson Intl., ON
• Vancouver, BC
• Victoria Intl., BC
• Halifax Intl., NS
• London, ON
• Québec City, Jean Lesage Intl., QC
• Whitehorse Intl., YT
• Winnipeg Intl., MB
• Yellowknife, NT
• Charlottetown, PE
• Fredericton, NB
• Prince George, BC
• Regina Intl., SK
• Saint John, NB
• Saskatoon, John G. Diefenbaker Intl., SK
• Thunder Bay, ON

Appendix 2 METAR weather phenomena

Appendix 3 Limited Aviation Weather Observations (LAWO)

Services provided in accordance with this appendix do not meet the requirements for routine or special aerodrome reports (METAR / SPECI).

A Limited Aviation Weather Observation or LAWO is an observation issued by an airport controller. It is designed to provide details on the observation of limited elements in order to support local flight operations.

These limited observations are normally included in the local ATIS recording and updated as required or passed verbally to aircraft arriving and departing the local airport.

These observations are not designed to be transmitted outside of the local control zone covered by the control tower as they only provide an indication of the conditions present at the airport from the vantage point of the tower cab. This indication can sometimes be slightly different from an observation that would be conducted from a regular exterior observation point.

Parameters that are required for the LAWO service are restricted to:

1. Tower visibility
2. Tower Ceiling

Definitions

Tower visibility

The prevailing visibility observed from inside the control tower cab.

Tower ceiling

A ceiling observed from inside the control tower cab.

Tower visibility

Prevailing visibility is the maximum visibility value common to sectors comprising one half or more of the horizon circle.

Requirements

In order to be able to report a tower prevailing visibility, the following requirements shall be met:

1. Visibility markers shall be used to determine the tower prevailing visibility.
2. A visibility marker chart with suitable markers shall be displayed at each LAWO site.
3. Only the markers shown on the visibility chart can be used in the determination of the tower visibility.

Procedures

1. To determine prevailing tower visibility, the horizon circle shall be divided into as many sectors as there are different values of visibility. The highest visibility value that is common to sectors which cover one half or more of the horizon circle shall be taken as the prevailing visibility.
2. The tower visibility shall be reported in statute miles and the following values shall be used:

   Increments of ⅛ SM	0	⅛	¼	⅜	½	⅝	¾
   Increments of ¼ SM	1	1 ¼	1 ½	1 ¾	2	2 ¼	2 ½
   Increments of 1 SM	3	4	5	6	7	8	up to 15
   Increments of 5 SM	20	25	30	35	etc. – shall be used only if suitable markers are available.

3. If the observed prevailing tower visibility is between two reportable values, the lower value shall be used.
4. Visibility at night shall be determined with the aid of markers in the form of lights. Very powerful or focused light should be used with caution, as their great penetrating power tends to result in too high a value for the visibility. However, obstruction lights on towers and buildings and the various marker lights around an airport may be used for visibility markers. Additionally, extreme caution must be used when determining visibility at night due to the fact that you observe from the inside of a lighted area (tower cab) that may affect your ability to properly assess the visibility value.
5. If suitable markers beyond 15 SM are lacking, 15 SM is the maximum reportable value.
6. Optical devices such as binoculars shall not be used by the observer when determining tower visibility.
7. If the observed tower visibility appears to be different from the prevailing visibility that would be observed at ground level, a remark indicating that the ground visibility is likely higher or lower than the tower visibility must be included in the information passed to pilots. When practical, the observer should provide an estimate of the ground visibility.
8. Should the visibility in one or more sector be different by half or less or by double or more than the reported prevailing visibility, the observer shall make every effort to supplement the prevailing visibility with a sector visibility remark to pilots as per NC-SWOP 3.7.
9. The use of other tools such as weather camera images to help determine tower visibility shall be approved by the competent authority before being allowed.
10. The reported tower visibility report shall be updated when the tower visibility decreases to less than or if below, increases to equal or exceed the following values:
    1. 3 SM
    2. 1 SM
    3. ¾ SM*
    4. ½ SM
    5. ¼ SM*
    6. The additional limits as specified in the Unit Operations Manual

Tower ceiling

Requirements

In order to be able to report a tower ceiling, the following requirements shall be met:

1. The layer shall be measured either by a laser ceilometer or when available by a known feature such as a mountain top, a pilot report or radar altitude readings for visually identified aircraft entering the layer.
2. The layer seen from the cab shall be either broken (BKN) or Overcast (OVC) or the vertical visibility (VV).
3. The controller shall be able to visually assess the layer extent from your observation point.

Procedures

1. An observation of the tower ceiling requires the examination and identification of the clouds and obscuring phenomena (fog, smoke, precipitation, etc.) which prevent an uninterrupted view of the sun, moon, stars or the clear blue of the celestial dome viewed from the inside of the tower cab.
2. Each layer is evaluated individually and then coded into a sky condition in accordance with the rules and procedures for coding sky condition included in NC-SWOP Chapter 5.
3. The tower ceiling to be reported is the height above the ground of the first layer that is coded as being broken or OVC or is the value of the VV into a surface-based layer that completely obscures the sky.
4. Layers that are present below the ceiling height shall also be reported. Should these layers not be detected by the ceilometer they shall be reported as layers below (example: Tower ceiling 3500 BKN, SCT below).
5. When all layers are measured, they shall be reported from the lowest to the highest (example: 1500 SCT, tower ceiling 2500 BKN, 4000 OVC).
6. If the ceilometer is unserviceable or does not identify the height of the ceiling layer, the controller shall be limited to report the tower ceiling as indeterminate unless you obtain a pilot reported ceiling, can use known measured features (mountains, buildings…) or radar altitude readings for visually identified aircraft at the local airport entering the layer.
7. If the airport lights prevent you from making an observation of the sky condition during night observations and the ceilometer is giving you a measurement then the controller shall report the ceiling as indeterminate (example: tower ceiling indeterminate, layer detected at 1900 feet).
8. The reported tower ceiling report shall be updated whenever ceiling decreases to less than, or if below, increases to equal or exceed the following values of height:
   • 1500 feet
   • 1000 feet
   • 500 feet
   • The additional limits as specified in the Unit Operations Manual.

Appendix 4 Specified non-METAR/SPECI aviation weather services

The provision of METAR / SPECI, by human or automated methods, and LWIS must be in full compliance with the requirements of The Standards for Weather Observing Programs in Part A of The Manual of Surface Weather Observation Standards.

For automated weather observation services, except for NAV CANADA services that provide AUTO METAR / SPECI and LWIS, the service provider shall either meet the requirements of QAMS Chapter 2.2 of MANOBS or the alternative quality assurance requirements below inpart A.3 of this appendix.

Notification Requirements for all specified non-METAR/SPECI aviation weather services:

1. the name, address and telephone number (and e-mail address, as applicable) of the service provider (The person named is responsible for all aspects of the service being provided and is liable for meeting all requirements);
2. the aerodrome or meteorological station, its elevation and the elevation of any pressure sensor with reference to a survey result or benchmark and its geographical coordinates, where the meteorological reports originate;
3. a summary description of the service to be provided including specification of the meteorological elements to be reported;
4.  method(s) by which meteorological reports will be disseminated;
5. the schedule (including specification of an ‘on request’ basis, as applicable), at which meteorological reports will be provided;

And, as applicable, each of the following:

6. the manufacturer, model, and type of meteorological instrumentation used to make the meteorological observations, as applicable;
7. a summary description of any irregularities with respect to the exposure of meteorological instruments;
8. the name, address, telephone number and e-mail address (as applicable), of the person providing calibration of the altimeters to be used;
9. the name, address and telephone number (and e-mail as applicable) of the person who inspected the aircraft altimeters to ensure compliance with the accuracy and quality control requirements of section 3 of part A.1 of this appendix.

A.1 Use of Dual Altimeters to report altimeter setting for Approach UNICOM

Meteorological observations of atmospheric pressure measured by dual aircraft altimeters shall not be used in the preparation of aviation routine aviation weather reports (METAR/SPECI).

Any services being provided in compliance with the exemption to The Manual of Surface Weather Observation Standards, as referenced by CAR 804.01 (1) (c), signed 1 April 2007, pertaining to the use of dual aircraft altimeter to provide reports of altimeter settings, will be deemed to be in compliance with these provisions upon publication.

1 Installation, siting, testing and maintenance

1.1 The service provider shall establish and follow all practices, procedures and specifications for safe operation and maintenance.

1.2 The service provider shall document all the practices, procedures and specifications established and followed in accordance with section 1.1 and shall provide all the relevant information to the Minister upon reasonable notice given by the Minister.

1.3 The service provider shall obtain written authorization to measure and report station atmospheric pressure from the operator of the aerodrome or station, where the services are being provided, and shall notify the operator of the aerodrome or station of any change to the level of service being provided.

1.4 The following shall apply to the installation, siting, safe operation and maintenance of the aircraft altimeters used to obtain station meteorological observations of atmospheric pressure and provided as meteorological reports of the current altimeter setting for an aerodrome or station:

1. A minimum of two independent aircraft altimeters, each meeting the requirements of Technical Standard Order (TSO) C-10b or C10c, or successor version, as adopted by the Airworthiness Manual Chapter - 537 Airworthiness Standards Appliances and Parts Subchapter B - Technical Standard Orders 537.103 shall be used;
2. The altimeters shall be of similar make, model and performance;
3. The altimeters shall each be located so as to measure supply data which is representative of the aerodrome or station for which the altimeter setting is required;
4. The altimeters shall be mounted in a box or instrument rack that precludes damage from mishandling and ensures a permanent location;
5. The position and height of the altimeters shall minimize reading errors due to parallax when viewed from the front and a step shall be available to offset such errors as necessary;
6. The altimeters shall be kept away free from sources of moisture or sources of forced ventilation or drafts near windows, and kept at a consistent temperature;
7. The altimeters shall not be located within a pressurized building or in a location within a building that may experience fluctuations in ambient air pressure due to wind venting or, forced air heating and/or cooling systems, or other causes that may induce an error of greater than one hundredth of an inch of mercury, equivalent;
8. The altimeters shall be vented to an outside vent, or a static source, should they not meet the conditions of paragraph (g);
9. The altimeters shall both be tagged, or otherwise marked, in plain view showing the following:
   1. the elevation of the altimeters above Mean Sea Level:
   2. the date of the last inspection of both altimeters;
   3. that they are “NOT FOR USE IN AIRCRAFT”; and
   4. that they are not to be used and shall be marked “UNSERVICEABLE” to provide the altimeter setting if the altimeter comparison differs by more than 5 hundredths of an inch of mercury.
10. The altimeters shall each be calibrated, at an avionics facility or other qualified facility where internal adjustments and repairs to an altimeter can be made, in accordance with the provisions of Canadian Aviation Regulation 571.02 and appendix B to the Airworthiness Manual within one year prior to installation and shall:
    1. meet the allowable scale error tolerances in Table I to Appendix B of the Airworthiness Manual up to and including for the full range of atmospheric pressures expected over the aerodrome for which the altimeters are intended for use;
    2. meet requirements for hysteresis up to and including the second test point greater in altitude than the elevation of the aerodrome for which the altimeters are intended for use for after effect and case leak test tolerance in Table II to Appendix B of the Airworthiness Manual and case leak and friction altitude tolerances in Table III to Appendix B of the Airworthiness Manual that are appropriate for the full range of atmospheric pressures and rates of change of atmospheric pressure expected over the aerodrome for which the altimeters are intended for use;
    3. meet the barometric scale error requirements of Table IV to Appendix B of the Airworthiness Manual with a tolerance of 25 feet; and
    4. include a correction card for each altimeter (if necessary) indicating any corrections that must be applied to obtain an accurate reading.
11. An on-site inspection by a qualified person shall be carried out following installation and prior to the first use of the altimeters to ensure that the accuracy provisions of section 3 to this appendix are met.

2 Observations and reports

2.1 The reference elevation used to compute the altimeter setting shall use the elevation of the aircraft altimeters measured to the nearest foot above or below mean sea level as determined from a nearby benchmark or survey.

2.2 The altimeter setting shall be read, from each altimeter, and rounded to the nearest lower hundredth of an inch of mercury.

2.3 The reading from each altimeter, pursuant to section 2.2 shall be corrected as indicated by the correction card supplied by the calibration facility in accordance with paragraph 1.4(j).

2.4 The airport or stations official meteorological report of altimeter setting reported by the service provider shall use the lower of the altimeter setting readings obtained pursuant to sections 2.1 to 2.3.

2.5 All meteorological reports of altimeter setting shall contain the following information:

1. the location station identifier;
2. the time of the altimeter reading; and
3. the altimeter setting rounded to the nearest lower hundredth of an inch of mercury.

2.6 All dates and times entered in a meteorological report shall be made with reference to the 24 hour clock in Coordinated Universal Time.

2.7 The meteorological report of altimeter setting shall be considered valid for a period of no more than 90 minutes.

2.8 Altimeter settings in excess of 31 inches of mercury shall be reported as “ALTIMETER SETTING IN EXCESS OF 31 INCHES”.

3 Accuracy and quality control

3.1 The difference in readings between the altimeters shall be 5 hundredths of an inch of mercury equivalent, or less.

3.2 The altimeters shall receive on-site inspections at least once each year to:

1. verify that each altimeter reads within 4 hundredths of an inch of mercury compared to the value of the inspection barometer; and
2. ensure both altimeters provide atmospheric pressure readings that are representative of the aerodrome or station for which they are intended.

3.3 The person performing the inspection pursuant to section 3.2 shall:

1. be independent from the manufacturer of the altimeters or from the service provider; and
2. have significant experience with meteorological instrumentation, access to an inspection barometer with a pressure standard adequate to verify accuracy to within 1 hundredth of an inch of mercury equivalent and have demonstrated experience in establishing traceability of measurements to a known standard.

3.4 If, following three immediately consecutive attempts to obtain a reading and the altimeters do not meet the tolerance required by section 3.1, then they shall be immediately tagged or otherwise clearly marked as unserviceable and shall be re-calibrated, or reconditioned or replaced prior to any further use.

3.5 If any of the altimeters do not meet the requirements of section 3.2, then they shall be immediately tagged or otherwise clearly marked as unserviceable and shall remain unserviceable until such time as an inspection by a qualified person shows that they meet these conditions.

3.6 The service provider shall ensure that the accuracy of the timing device used to establish the time of the meteorological observation is accurate to within 1 minute of the Coordinated Universal Time.

3.7 The service provider shall establish and maintain documentation containing:

1. the following meteorological station information:
   1. contact information for the service provider and the qualified person providing maintenance services for the meteorological station;
   2. contact information for the qualified person providing inspection services for the aircraft altimeters;
   3. contact information for the calibration facility that calibrated the aircraft altimeters;
   4. location of the aircraft altimeters within the building;
   5. station climatological description;

   6. the person(s) authorized by the service provider to take observations and disseminate reports;

      Note: The inclusion of photographs of the equipment or the details of its location in the service documentation are recommended.

   7. the following information for each altimeter:
      1. the type including manufacturer, model and serial number;
      2. written confirmation of the date and results of the last calibration;
      3. the correction card resulting from the last calibration; and
      4. written confirmation of the date and results of the last inspection.

4 Training

4.1 The service provider shall ensure, and maintain documentation showing, that a qualified person(s) providing meteorological observations of atmospheric pressure obtained from aircraft altimeters, and provided as meteorological reports of the current altimeter setting to be used to permit the execution of instrument procedures, has/have received training which includes, as a minimum:

1. adjusting the altimeter setting button until the known altitude of the altimeter above mean sea level is indicated on the subscale;
2. activating any buzzer mechanism or tapping the instrument to eliminate effects due to friction of the mechanism;
3. reading both the altimeters and interpolating values as necessary;
4. using the correction cards;
5. determining the correct reading in accordance with section 3;
6. established quality assurance routines including the comparison of the determined altimeter setting value with previous or nearby altimeter settings;
7. approved dissemination methods; and
8. the use and importance of the altimeter setting in civil aviation.

4.2 The service provider shall provide to the Minister, upon reasonable notice given by the Minister, a copy of the documentation required by section 5.1.

A.2 Assessment of wind direction and speed for Approach UNICOM

Any services being provided in compliance with the exemption to The Manual of Surface Weather Observation Standards, as referenced by CAR 804.01 (1) (c), signed 1 February. 2007 pertaining to the assessment and reporting of wind direction and speed for Approach UNICOM, will be deemed to be in compliance with the provisions of this appendix upon its publication.

1.1 No person shall assess wind direction and speed in support of a straight in landing from an instrument procedure unless the aerodrome has a wind direction indicator that meets the requirements of subsection 301.06 of the Canadian Aviation Regulations.

1.2 The wind direction indicator pursuant to 1.1 shall have a functioning light source should the meteorological observation be made at night.

1.3 The wind direction and speed shall be specifically reported as “estimated” unless measured in accordance with the full requirements as otherwise set out in Chapter 3 of The Manual of Surface Weather Observation Standards and / or with the use of instrumentation that meets the requirements of Chapter 12 of The Manual of Surface Weather Observations Standards.

1.4 The service provider shall obtain authorization to report station wind direction and speed from the operator of the aerodrome or station, where the services are being provided, and shall notify the operator of the aerodrome or station of any change to the level of service.

1.5 All meteorological reports and record thereof of estimated wind direction and speed shall contain the following information:

1. aerodrome or station name or location identifier;
2. time of the meteorological observation, to the nearest minute;
3. notice that the wind direction and speed are “estimated.”
4. whether the wind direction is based on true or magnetic direction.

1.6  The qualified person shall immediately report the wind direction and speed as assessed and the time of the observation to the nearest minute in accordance with 1.5, to the person who requested the report.

1.7 The meteorological observation of wind direction and speed shall be considered current for a period not exceeding ten minutes.

1.8 The qualified person estimating wind shall not report any other elements of a meteorological report unless done so in accordance with the applicable requirements of The Manual of Surface Weather Observation Standards.

1.9 Wind direction and speed shall be estimated:

1. by a qualified person;
2. only to the nearest 8 points of the compass from which it is blowing; and
3. based on its effects upon:
   1. the aerodrome wind direction indicator(s) and;
   2. using the Beaufort wind scale, in an exposed out-of-doors location.

1.10 The training to estimate wind direction and speed shall ensure, at a minimum, that the qualified person:

1. understands and has successfully demonstrated, under practical conditions, correct procedures for using all appropriate aids to estimate the wind direction and speed, including as applicable:
   1. use of the aerodrome or station wind direction indicator(s);
   2. use of the Beaufort wind scale;
   3. use of any instrumental aids; and
   4. all other available and appropriate aids.
       

   b. has demonstrated an estimation accuracy that differs by no more than one scale of the Beaufort wind scale or equivalent, from the actual wind speed;

   c. understands and has demonstrated, under practical conditions, how to estimate and report the wind direction and speed;

   d. understands the difference between true and magnetic compass directions and when and how to use each, as  applicable;

   e. knows the orientation and numbering of the runway(s) at the aerodrome;

   f. has demonstrated knowledge, to at least the 8 points of the compass, of the directions from the point of observation;

   g. understands and has demonstrated correct use of dissemination procedures for meteorological reports in accordance with section 1.5;

   h. understands the need to keep the wind direction indicator in good condition and free from accumulations of ice, snow, nesting activity or other objects and knows the contact procedures to initiate maintenance, as necessary.

A.3 Quality control for specified automated weather observations

The provision of METAR / SPECI, by human or automated methods, and LWIS must be in full compliance with the requirements of The Standards for Weather Observing Programs in Part A of The Manual of Surface Weather Observation Standards.

Other service providers who provide aviation weather services consisting of automated observation and reporting of any or all of the following: wind direction, speed and character; visibility; present weather; sky condition; temperature; dewpoint temperature or atmospheric pressure using automated weather observation systems shall meet either the requirements for Quality Assurance Management Systems in Section 2.2 of Chapter 2 of the Manual of Surface Weather Observation Standards or the quality assurance established below.

The service provider shall establish and maintain a station history at the meteorological station for each station that it operates containing:

1. the type of the meteorological system;
2. the following meteorological station information including:
   1. contact information for the service provider and the person providing maintenance services for the meteorological station;
   2. location using geographical coordinates and elevation;
   3. descriptions of remote and immediate surroundings and obstacles;
   4. instrument layout;
   5. facilities including data transmissions, power supply and cabling; and
   6. climatological description; and
3. the following individual instrument information including:
   1. type including manufacturer, model, serial number, and operating principles;
   2. performance characteristics;
   3. calibration data and time;
   4. siting and exposure including location, shielding and height above ground;
   5. measuring or observing program;
   6. time of meteorological observations;
   7. data acquisition including sampling and averaging;
   8. data processing methods and algorithms;
   9. preventive and corrective maintenance; and
   10. data quality

4. A description of the training provided to any personnel providing commissioning, inspection or maintenance services;
5. station operation manuals used by staff providing services;
6. a description of the minimum qualifications, training and currency limitations established by the service provider for staff providing services.