MANOBS Manual of Surface Weather Observations: aviation routine weather report

16.1 General

Detailed coding instructions for each element of each group of the Aviation Routine Meteorological Report (METAR) code are given below, although not necessarily in the order in which elements are observed or that entries will be made by the observer. The type of report is usually determined after all other data have been observed. The observer may find that some weather elements are automatically encoded; however, the observer will need to possess a basic understanding of how these weather elements are observed.

16.2 Symbolic form of the Canadian METAR code

METAR or Special report (SPECI) CCCC YYGGggZ AUTO BBB dddffGfmfmKTdndndnVdxdxdxVVVVSM (RDRDR/VRVRVRVRFT/i or RDRDR/VRVRVRVRVVRVRVRVRFT/i) w’w’ (NsNsNshshshs and/or VVhshshs) T’T’/T’dT’dAPHPHPHPH(WS RWYDRDR or WS ALL RWY) RMK (Layer type and amount general remarks) SLPppp

Symbols shown in bold in the symbolic form above are included verbatim as part of the message, whenever the relevant group is included in the message. All other symbols are replaced by appropriate data as applicable.

16.3 The METAR code - detailed description and coding instructions

16.3.1 Type of report (METAR or SPECI)

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

METAR is the name of the international meteorological code for an Aviation Routine Weather Report. METAR observations are normally taken and disseminated on the hour.

SPECI is a report issued when selected changes in weather conditions significant to aviation occur off the hour. (See 16.4.4 for detailed SPECI criteria.).

16.3.1.1

When an hourly observation (during the period H-5 to H) reveals that one or more of the criteria specified as requirements for SPECI observations has occurred, the observation shall be designated as a METAR and released on the hour. By exception, threatening severe weather (see Introduction, Priority of Duties) shall require the immediate dissemination of a SPECI observation.

Note: Segments in examples of coded messages are bolded to highlight the section described.

16.3.2 International Civil Aviation Organization (ICAO) station identifier (CCCC)

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

Example: Weather observation from Toronto Lester B. Pearson International Airport.

METAR CYYZ 040600Z 35006KT 15SM BKN250 12/M01 A3013 RMK CI5 SLP208

16.3.3 Date/time of observation and other indicators (YYGGggZ AUTO BBB)

The date/time of observation (YYGGggZ) shall be included in all reports. The date and time of observation on the hour is used for all METAR reports. In SPECI reports the time refers to the time of occurrence (hour and minutes) of the change(s) in observed elements that required the issue of the SPECI report. The exception is with reporting the end of thunderstorms and precipitation. (See 16.4.4.6 and 16.4.4.7.)

YY: Day of month

GG: Hour of the day

gg: Minute of the hour

Z: Indicates UTC

AUTO: Automatic station indicator. Indicates the report is from an auto station

BBB: Correction indicator. 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.

Example (1): An automated aviation report taken at Moosonee (CYMO) airport on the 4th day at 0600Z.

METAR CYMO 040600Z AUTO 30002KT 9SM FEW014 BKN024 OVC085 01/01 A2976 RMK SLP078

Example (2): A special aviation observation taken at Quebec City Jean Lesage International (CYQB) Airport on the 10th day at 1211Z.

SPECI CYQB 101211Z 25007KT 4SM -SHRA BR BKN020TCU 13/12 A3003 RMK TCU6 SLP171

Example (3): Weather observation taken at Calgary International (CYYC) Airport on the 5th day at 1200Z. This is the second correction to the 1200Z METAR.

METAR CYYC 051200Z CCB 31009KT 40SM FEW050 BKN160 OVC240 07/M03 A2980 RMK CU1AC5CI2 SLP098

16.3.4 Wind velocity (dddffGfmfmKT)

ddd: The two-minute mean wind direction from which the surface wind is blowing and is always three digits, given in degrees true but rounded off to the nearest 10 degrees.

ff: The two-minute mean wind speed; two digits if under 100, three digits if over 100. (see 7.1.2.)

Gfmfm: Gust information will be included if gust speeds exceed the two-minute mean wind speed (ff) by 5 knots or more and the highest peak is at least 15 knots in the 10-minute period preceding the observation. If this condition is not met, this group shall not be reported. G indicates gust and fmfm is the peak gust speed reported, using two or three digits as required.

KT: Indicates the units are knots.

Note (1): When suitable wind instruments are lacking, or when the wind instruments are not in operating condition, the wind direction and speed shall be estimated (see 7.4) and remarks entered. (see 16.3.13.2.1.) Use the Beaufort scale knots average for the speed.

Example: Wind estimated 230 degrees true at 9 knots

METAR CYYC 051200Z 230009KT 15SM FEW050 BKN160 OVC240 07/M03 A2980 RMK CU1AC5CI2 WND ESTD SLP098

Note (2): CALM wind is reported for mean wind speeds of less than 2 knots.

Example: Calm wind.

SPECI CYQB 101211Z 00000KT 4SM BR FEW020 13/12 A3003 RMK FG1SC1 SLP171

Note (3): When squalls are observed, the peak wind speed shall be reported as a gust and “SQshall be reported in present weather. (see 7.1.3.2.)

Example: Squall with a peak wind speed of 36 knots.

METAR CYYT 241400Z 25015G36KT 10SM SQ OVC009 17/13 A2979 RMK SF8 VIS LWR N SLP089

Note (4): In the case of variable wind direction, ddd shall be coded as VRB when the wind speed is less than 3 knots. 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.

Example (1): Wind direction is varying from 030 degrees to 140 degrees and the mean wind direction is 080 degrees but the mean wind speed is 2 knots.

METAR CYQB 041500Z VRB02KT 30SM FEW040 18/10 A3003 RMK SC2 SLP169

Example (2): Wind direction is varying from 030 degrees to 240 degrees and the mean wind direction is undeterminable. The mean wind speed is 4 knots.

METAR CYQB 041500Z VRB04KT 30SM FEW040 18/10 A3003 RMK SC2 SLP169

16.3.5 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.

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 knots or greater, the observed two extreme directions between which the wind has varied shall be given for dndndnVdxdxdxin clockwise order. Otherwise the group shall not be included.

Example: Wind direction is varying from 060 degrees to 133 degrees. The mean wind direction is 100 degrees. The mean wind speed is 9 knots.

METAR CYQB 041300Z 10009KT 060V130 30SM FEW040 BKN070 16/09 A3003 RMK SC2AC4 SLP169

16.3.6 Prevailing visibility (VVVVSM)

The prevailing visibility shall be reported in statute miles and fractions of statute miles followed by the letters "SM" to indicate units. If the observed prevailing visibility is between two reportable values, the "lower" value shall be used (see 2.3).

VVVV: Prevailing visibility

SM: Indicates the units are statute miles

16.3.6.1 Reportable visibility values

The following values (in statute miles) shall be used for reporting visibility:

This table provides the reportable visibility values.
Increments of 1/8 SM 0 1/8 1/4 3/8 1/2 5/8 3/4
Increments of 1/4 SM 1 1 1/4 1 1/2 1 3/4 2 2 1/4 2 1/2
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.

Note: If suitable markers beyond 15 miles are lacking, 15 SM is the maximum reportable value.

Example: Prevailing visibility is observed as 3/4 SM.

METAR CYVR 241600Z 29005KT 3/4SM BR SCT015 SCT230 15/15 A3018 RMK FG2SF1CI1 SLP219

16.3.6.2 Sector visibilities

Sector Visibilities that are half or less, or double or more of the prevailing visibility shall be reported in Remarks.

Example (1): The prevailing visibility is 15 SM; visibility to the north quadrant is observed to be 3 SM.

METAR CYTH 241800Z 13017KT 15SM FEW020 FEW220 15/07 A3011 RMK SF1CI1 VIS N 3 SLP205

Example (2): The prevailing visibility is 3 SM; visibility to the south quadrant is observed to be 6 SM.

METAR CYGK 201600Z 11003KT 3SM BR FEW020 08/07 A2948 RMK FG1SC1 VIS S 6 SLP980

16.3.6.3 Variable visibility

If the prevailing visibility is observed to be fluctuating rapidly and increasing and decreasing from a mean value by 1/4 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.

Example (1): Prevailing visibility of 1 SM is varying between 3/4 and 1 1/4 SM.

METAR CYHZ 241800Z 35009KT 1SM BR OVC008 16/14 A2986 RMK SF8 VIS VRB 3/4-1 1/4 SLP112

Example (2): Prevailing visibility of 3 SM is varying between 1 SM and 5 SM.

METAR CYTS 251800Z 06010G25KT 3SM BLSN SKC M12/M15 A3041 RMK VIS VRB 1-5 SLP311

16.3.6.4 Point of observation

When observing visibility from elevated positions, such as a control tower or roof (see 2.6.1) and the visibility differs by a reportable value or more 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.

Example: Prevailing visibility is 3 SM in blowing snow; however, visibility from the roof is observed to be 10 SM.

METAR CYXU 251100Z 06015G25KT 3SM BLSN BKN025 M09/M10 A3026 RMK SC6 ROOF VIS 10 SLP248

16.3.6.4.1

With "blowing snow" conditions, the reporting of roof-top visibility is particularly important. Frequently, visibility is much better a short distance above ground level. Ground-level visibility alone in such circumstances does not give a full description of the visibility that would be experienced by the pilot of an aircraft.

16.3.6.4.2

Low-lying "fog" usually occurs with a clear sky or high thin cloud conditions. The observer should provide an estimate of the depth of the fog as well as the roof-top visibility.

Example: Prevailing visibility is 1/4 SM in fog; visibility from the roof is 10 SM. The fog is estimated by the observer to be 30 feet thick.

METAR CYSJ 081300Z 15012KT 1/4SM FG OVC230 08/08 A3003 RMK FG6CI2 ROOF VIS 10 FG 30FT THK SLP170

16.3.7 Runway visual range (RDRDR/VRVRVRVRFT/i)

Where RVR data are displayed, they shall be included in the METAR and SPECI observations for the active - or most aligned into the wind -runway(s) when the prevailing visibility is 1 SM or less and/or the RVR value for the designated runway(s) is 6000 feet or less. RVR data for runway(s) other than the active or most-aligned into-the-wind may be included. Stations with the capability to display values for multiple RVRs may record and transmit a maximum of four RVR values. All RVR values transmitted shall be representative of the touchdown zone of the active landing runway(s).

R: Group indicator that precedes the runway visual range information.

DRDR: Designator of each runway for which runway visual range is reported. Parallel runways should be distinguished by appending to DRDR the letters L, C or R indicating the left, central or right parallel runway, respectively. A suitable combination of these letters is used for up to, and including, five parallel runways (i.e. LL, L, C, R, RR). The letter(s) shall be appended to DRDR as necessary in accordance with the standard practice for runway designation.

VRVRVRVRFT: The 10-minute average runway visual range immediately preceding the observation. However, when the 10-minute period includes a marked discontinuity in the RVR (for example, sudden advection of fog, rapid onset or cessation of an obscuring snow shower), only the data after the discontinuity shall be used for obtaining mean RVR values and variations thereof, hence the time interval in these circumstances shall be correspondingly reduced. FT shall be appended to the measurement to indicate that the measurement is in feet.

i: Indicates the RVR trend. If the runway visual range values during the 10-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 minutes of the period, this shall be indicated by i = U for upward and i = D for downward tendency of runway visual range values. When no distinct change in runway visual range is observed, i = N shall be used. When it is not possible to determine the tendency, i shall be omitted. When the tendency is not displayed, i shall be omitted.

Example: The RVR for runway 33 is 4000 feet and the observed trend is down.

METAR CYXE 292000Z 30015G25KT 3/4SM R33/4000FT/D -SN BLSN BKN008 OVC040 M05/M08 A2992 RMK SF5SC3 SLP170

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

When the RVR at a runway varies significantly and when during the 10-minute period preceding the nominal observation time, the one-minute mean extreme values assessed vary from the mean value 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 given in that order in the form RDRDR/VRVRVRVRVVRVRVRVRFT/i instead of the 10-minute mean. The tendency shall also be indicated.

R: See 16.3.7

DRDR: See 16.3.7

VRVRVRVRVVRVRVRVR: The minimum one-minute mean RVR value followed by the maximum one-minute mean RVR value during the 10-minute period preceding the observation. These two values will be separated by the letter "V" indicating variable conditions.

i: See 16.3.7

Example: The RVR for runway 33 is varying between 1000 feet and 2400 feet; the trend is upward.

METAR CYXE 081200Z 30010KT 3/8SM R33/1000V2400FT/U SN VV004 M05/M06 A3002 RMK SN8 SLP170

16.3.7.2

When actual RVR values are outside the measuring range of the observing system in use, the following procedure shall apply:

  • When the RVR is greater than the maximum value that can be assessed with the system in use, a P shall be appended to the group VRVRVRVR i.e., P6000. The METAR encoder will convert this to the ICAO standard.
  • When the RVR is below the minimum value that can be assessed with the system in use, an M shall be appended to the group VRVRVRVR i.e., M0600. The METAR encoder will convert this to the ICAO standard.

16.3.8 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 16.3.8.1).

16.3.8.1 WMO Code Table 4678

Significant present and forecast weather codes. The w'w' groups shall be constructed by considering columns 1 to 5 in the following table in sequence; that is intensity, followed by description, followed by weather phenomena. An example could be: +SHRA (heavy shower(s) of rain).

Qualifier
1-
Intensity or proximity
Qualifier
2
Descriptor
Weather phenomena
3
Precipitation
Weather phenomena
4
Obscuration
Weather phenomena
5
Other

- Light

Moderate (no qualifier)

+ Heavy (well-developed in the case of dust/sand whirls, dust devils and funnel clouds)

VC In the Vicinity

MI Shallow

BC Patches

PR Partial (covering part of the aerodrome)

DR Low Drifting

BL Blowing

SH Shower(s)

TS Thunderstorm

FZ Freezing (supercooled)

DZ Drizzle

RA Rain

SN Snow

SG Snow Grains

IC Ice Crystals (diamond dust)

PL Ice Pellets

GR Hail

GS Small Hail and/or Snow Pellets

UP Unknown Precipitation (AWOS only)

BR Mist

FG Fog

FU Smoke

VA Volcanic Ash

DU Widespread Dust

SA Sand

HZ Haze

PO Dust/Sand Whirls (dust devils)

SQ Squalls

FC Funnel Cloud(s) (tornado or water-spout)

SS Sandstorm

DS Duststorm

16.3.8.2 Qualifiers

Weather phenomena are preceded by one or two qualifiers, one of which describes either the intensity or proximity to the station of the phenomena, the other of which describes the phenomena in some other manner.

16.3.8.3 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. (See 3.9 - Intensity of precipitation.)

  1. Intensity shall be indicated for the following:
    • precipitation (light, moderate, heavy)
      Note: Not applicable to ice crystals
    • showers (light, moderate, heavy)
    • precipitation associated with thunderstorms (light, moderate, heavy)
    • blowing dust, blowing sand or blowing snow (moderate, heavy)
    • dust storm or sandstorm (moderate, heavy)
    • tornadoes or waterspouts shall be reported as heavy (+FC)
  2. 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. Freezing precipitation shall be reported as a separate group. (See par. 16.3.8.6.)
  3. Intensity shall not be applied to precipitation associated with the proximity qualifier "VC".

Example (1): Light rain and mist.

METAR CYFC 251300Z CCA 36011KT 6SM -RA BR FEW009 OVC031 07/06 A3012 RMK SF2SC6 SLP199

Example (2): Moderate rain and light snow are occurring at the same time.

METAR CYHZ 231700Z 10006KT 6SM RASN OVC008 01/01 A2980 RMK SC8 SLP098

16.3.8.4 Vicinity

The vicinity qualifier VC shall be used when specific weather phenomena are observed within 5 SM, but are not occurring at the point of observation. Tornadoes, funnel clouds and waterspouts shall be reported as occurring "at the station" when within sight (at any distance). 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(duststorm)
  • VCSS(sandstorm)
  • VCVA(volcanic ash)

Example: Light snow showers are observed in the vicinity; drifting snow is occurring at the site.

METAR CYXE 231700Z 31012G17KT 12SM VCSH DRSN BKN028 M15/M18 A3019 RMK SC6 SLP269

16.3.8.5 Descriptors

Descriptors provide further clarification to the weather phenomena that are being observed. This becomes critical when observing obstructions to vision. The only exception is when widespread dust, volcanic ash or other weather phenomenon is observed (see 16.3.8.6 (2) and (3)). No present weather (w'w') group shall have no more than one descriptor.

The descriptors MI(shallow), BC(patches) and PR(partial) shall be used only in combination with fog (FG). (See 3.5.2.5, 3.5.2.6 and 3.6.2.)

Example: Shallow fog is observed.

METAR CYVR 231900Z 10004KT 7SM MIFG OVC047 03/03 A3050 RMK SC8 SLP328

The descriptors DR (drifting) and BL (blowing) shall be used only in combination with snow (SN), dust (DU) and sand (SA). (See 3.5.4, 3.5.8 and 3.6.1.)

Example: Drifting snow is observed.

METAR CYBG 301200Z 26009KT 8SM -SN DRSN SCT030 M18/M21 A3017 RMK SC4 SLP234

When blowing snow (BLSN) is observed with snow (SN), both phenomena shall be reported. When the observer cannot determine whether or not snow is also falling due to heavy blowing snow then only +BLSN shall be reported. (See 3.5.4.)

Example: Blowing snow is observed.

METAR CYMU 301300Z 23020KT 3/4SM -SN BLSN OVC020 M17/M19 A2982 RMK SN1SC7 SLP109

SH (shower) shall be used in combination with one or more of the precipitation types rain (RA), snow (SN), ice pellets (PL), hail (GR) and snow pellets (GS). (See 3.4.3.2 for SHGS and 3.4.3.5 for SHGR.)

Example: Rain showers are observed.

METAR CYXX 301300Z 06003KT 7SM -SHRA BKN018 OVC035 01/M02 A2992 RMK SC6SC2 CVCTV CLD EMBD SLP 134

TS(thunderstorm) (see 3.3) shall be reported alone or in combination with one or more of the precipitation types rain (RA), snow (SN), ice pellets (PL), hail (GR) and snow pellets (GS).

Example: Thunderstorms and heavy rain showers are observed.

METAR CYXU 301500Z 15012KT 10SM +TSRA BKN024CB 27/19 A2993 RMK CB6 SLP134

FZ (freezing) shall be used only in combination with the weather types drizzle (DZ), rain (RA) and fog (FG). (See 3.4.2and 3.5.3.1.)

Example: Freezing fog is observed.

METAR CYAM 301300Z 00000KT 1/4SM R12/1200FT/N FZFG VV001 M13/M13 A3011 RMK FG8 SLP211

16.3.8.6 Weather phenomena

16.3.8.6.1 Precipitation

See Appendix III. If different types of precipitation are combined in one group, the predominant type as determined by intensity shall be reported first. The intensity qualifier selected represents the overall intensity of the entire group, not just one component of the group. The one exception is freezing precipitation (FZRA and FZDZ), which shall always be reported as a separate w'w' group. Ice crystals shall be reported regardless of the prevailing visibility.

16.3.8.6.2 Ice Crystals

To meet Canadian standards, when ice crystals (IC) are observed it shall be reported in the METAR / SPECI with any visibility.

16.3.8.6.3 Obstruction to vision

See Appendix III. An obstruction to vision is generally reported if the prevailing visibility is 6 miles or less. If an obstruction to vision is reported when the prevailing visibility is greater than 6 miles, the weather phenomena shall be reported with a descriptor, except when widespread dust (DU) or volcanic ash (VA) is observed.

16.3.8.6.4 Other

See Chapter 3. When one of these weather phenomena is observed no descriptor shall be included. In the case of FC being reported the observer shall report in Remarks if it is a funnel cloud, tornado or a water spout (See 16.3.13.2.3). The letter abbreviation SQ shall be used to report squalls when a sudden increase in wind speed is observed of at least 16 knots, the speed rising to 22 knots or more and lasting for at least one minute.

Example: Squall is observed.
METAR CYGR 051800Z 27025G35KT 8SM SQ BKN005 OVC010 05/02 A2923 RMK SF5SF3 SLP897

16.3.8.7 Present weather

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

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

16.3.8.8

When more than one weather phenomenon other than a precipitation combination is observed, each weather phenomenon shall be reported in a separate w'w' group in the order of the columns from WMO Code table 4678; Precipitation, Obscuration, and Other (see 16.3.8.1).

Example (1): Light rain and light snow are observed.

SPECI CYDP 051916Z 03017KT 6SM -RASN OVC004 01/00 A2945 RMK ST8 SLP974

Example (2): Fog observed; temperature minus 1.0°C; visibility less than 5/8 SM. FZFG shall be reported whether or not evidence of rime ice deposit exists.

METAR CYSL 051800Z 30004KT 1/2SM FZFG OVC005 M01/M01 A2937 RMK FG5SC3 SLP956

Example (3): A thunderstorm with moderate rain shower is observed.

SPECI CYGQ 082346Z 23002KT 8SM TSRA FEW008 BKN015CB 18/17 A2962 RMK SF1CB6 SLP072

Example (4): A rain shower is observed in the vicinity of the station but is not occurring at the station.

METAR CYQK 082200Z 28012G22KT 15SM VCSH BKN030 OVC120 16/10 A2976 RMK CU6AC2 SLP080

Example (5): Light snow and blowing snow are observed.

METAR CYYZ 301800Z 26013G22KT 5SM -SN BLSN BKN030 OVC070 M05/M11 A2976 RMK SC6AC2 SLP088

Example (6): A thunderstorm with moderate rain shower, hail and a tornado are observed at the station at 2012Z.

SPECI CYGK 312012Z 27022G28KT 3SM TSRAGR+FC SCT010 OVC030CB 25/23 A2977 RMK SF4CB4 TORNADO S MOVG E FRQ LTGCG ALQDS HAIL DIAM 12 MM SLP080

16.3.9 Sky condition

All layers of cloud or weather phenomena that are observed shall be reported as a layer aloft and entered in Remarks (see examples in 16.3.9.8). Only significant convective clouds, whose base is observed, shall be identified by appending the letter abbreviations CB (cumulonimbus) or TCU (towering cumulus), as appropriate, to the cloud group without a space. When a layer consists of two or more cloud types, e.g., CU (cumulus) and SC (stratocumulus), the predominating type by amount shall be recorded. If a cloud layer consists of any amount of TCU or CB, the TCU or CB shall be reported as the predominant type. 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.

When observing a surface-based layer, the amount of this phenomenon is added to the amount of the first layer aloft and then reported in accordance with 16.3.9.3. The surface-based layer that is observed shall then be reported in Remarks with the appropriate weather abbreviation (refer to Appendix III for abbreviations) and amount observed. This will then be followed by any types of layers aloft observed with the appropriate abbreviations and the amount of each layer aloft type. The sequence of reporting will be by the lowest level to the highest level with no spaces in between.

16.3.9.1 Layers aloft (NSNSNShShShS)

This group is used to report sky condition for layers aloft. This includes clouds and any amount of weather phenomena that is aloft. The amount of any surface-based obscuration shall be added to the coverage amount of any layers aloft to calculate the summation amount.

NSNSNS: The amount of each layer shall be determined using the summation amount principle and reported using the three-letter symbol abbreviations (see 16.3.9.2) followed, without a space, by the height of the base of the layer hShShS.

hShShS: The height of layers aloft shall be reported to the nearest:

  • 100 feet from the surface up to 10 000 feet
  • 1000 feet above 10 000 feet

The layers aloft group shall be repeated to report each layer aloft starting with the lowest layer. If there are no clouds the abbreviation SKC shall be used alone.

Note: If the actual observed height is halfway between any two values that satisfy the increments in 16.3.9.1 (ii), the lower value shall be used.

16.3.9.2 Cloud amount

Layer amount is the amount in oktas of the whole sky that is observed to be covered (not necessarily concealed) by a layer aloft or concealed by a surface-based layer.

This table provides terminology used for Sky Cover and the 3-letter Symbol Abbreviation used for recording to indicate Cloud Amount.
Three-letter symbol abbreviation Terminology Layer as defined by summation amount
SKC sky clear No cloud or layer present
FEW few Less than 1/8 to 2/8 summation amount
SCT scattered 3/8 to 4/8 summation amount
BKN broken 5/8 to less than 8/8 summation amount
OVC overcast 8/8 summation amount

16.3.9.3 Determining layer height

When determining the height of a layer aloft or vertical visibility the following order of priority shall apply:

  1. Measured
  2. Aircraft
  3. Balloon* (daylight hours, ceiling 1000 ft or less)
  4. Estimated

*Note: It is not required to release a ceiling balloon if there is a laser ceilometer in operation.

16.3.9.4 Vertical visibility (VVhShShS)

Vertical visibility (VV) shall be reported when the sky is obscured and information on vertical visibility is available. The existence of a vertical visibility will constitute an obscured ceiling.

VV: Group indicator that precedes the vertical visibility information.

hShShS:Vertical visibility shall be reported to the nearest:

  • 100 feet from the surface up to 10 000 feet
  • 1000 feet above 10 000 feet

Note: If the actual observed height is between any two values that satisfy the increments in paragraph 16.3.9.4 hShShS, the lower value shall be used.

Example (1): Sky obscured by snow.

METAR CYDF 182100Z 25005KT 1/4SM +SN VV002 M02/M02 A2926 RMK SN8 SLP911

Example (2): The vertical visibility is observed as 250 feet in fog.

METAR CYGK 241800Z 23005KT 1/4SM FG VV002 09/09 A2936 RMK FG8 SLP963

16.3.9.5 Variable heights

When the height of a layer aloft or into a vertical visibility is observed to be "variable", i.e., increasing and decreasing from the mean value by 1/4 or more of the mean value, the range of variation shall be indicated in Remarks.

Example: The vertical visibility into a surface-based obscuration is observed as variable between 200 and 400 feet, with a mean value of 300 feet.

METAR CYYR 121100Z 29013KT 1SM -SN DRSN VV003 M09/M11 A2945 RMK SN8 CIG VRB 2-4 SLP976

16.3.9.6 Ceiling

Ceiling is the lesser of the height above ground or water of the base of the lowest layer of cloud where the summation amount exceeds half the sky (more than 4/8); or the vertical visibility in a surface-based layer that completely obscures the whole sky.

16.3.9.7 Variable Ceiling

When the ceiling is 3000 feet or less and is observed to be “variable,” i.e., rising and falling from the mean value by 1/4 or more of the mean value (see 1.6.5), the range of variation shall be indicated in Remarks.

Example: Overcast ceiling (700 ft) varies between 500 and 900 feet.
METAR CYYT 071800Z 26004KT 1 1/2SM BR OVC007 00/00 A2926 RMK SC8 CIG VRB 5-9 SLP910

16.3.9.8 Sky condition examples

Example (1):

Celestial Dome, Example 1 (See long description below)
Description of image

The following Celestial Dome illustration provides an example with no cloud or surface based obscuration.

Observed: No cloud or surface-based obscuration.

Reported: METAR CYOW 061800Z 30015KT 15SM SKC M07/M10 A2974 RMK SLP079

Example (2):

Celestial Dome, Example 2 (See long description below)
Description of image

The following Celestial Dome illustration provides an example with TCU (2/8) and CB (1/8) based at 2000 feet.

Observed: TCU (2/8) and CB (1/8) based at 2000 feet.

Reported: METAR CYPQ 311800Z 30015KT 15SM SCT020CB 24/18 A2947 RMK CB3 CB NW SLP979

Example (3):

Celestial Dome, Example 3 (See long description below)
Description of image

The following Celestial Dome illustration provides an example with no cloud, Mist (2/8), visibility 2 SM.

Observed : No cloud, Mist (2/8), visibility 2 SM.

Reported : METAR CYSN 061700Z 30004KT 2SM BR SKC 09/08 A2994 RMK FG2 SLP140

Example (4):

Celestial Dome, Example 4 (See long description below)
Description of image

The following Celestial Dome illustration provides an example with SC (1/8) based at 2000 feet, AC (trace) based at 8000 feet.

Observed: SC (1/8) based at 2000 feet, AC (trace) based at 8000 feet.

Reported: METAR CYTS 061800Z 30010G15KT 15SM DRSN FEW020 FEW080 M13/M15 A3001 RMK SC1AC1 SLP190

Example (5):

Celestial Dome, Example 5 (See long description below)
Description of image

The following Celestial Dome illustration provides an example with FG (4/8), SC (1/8) based at 2000 feet.

Observed: FG (4/8), SC (1/8) based at 2000 feet.

Reported: METAR CYMX 062000Z 26003KT 1/2SM FG BKN020 05/05 A2965 RMK FG4SC1 SLP045

Example (6):

Celestial Dome, Example 6 (See long description below)
Description of image

The following Celestial Dome illustration provides an example with BR (2/8), SC (1/8) based at 2000 feet, AC (3/8 visible) based at 8000 feet, CI (2/8 visible) based at 23000 feet.

Observed: BR (2/8), SC (1/8) based at 2000 feet, AC (3/8 visible) based at 8000 feet, CI (2/8 visible) based at 23 000 feet.

Reported: METAR CYXX 071400Z 07008KT 4SM BR SCT020 BKN080 OVC230 07/07 A3020 RMK FG2SC1AC3CI2 SLP230

Example (7):

Celestial Dome, Example 7 (See long description below)
Description of image

The following Celestial Dome illustration provides an example with FG (6/8), SC (1/8) based at 2000 feet, CI (1/8) based at 23000 feet.

Observed: FG (6/8), SC (1/8) based at 2000 feet, CI (1/8) based at 23 000 feet.

Reported: METAR CWCA 071500Z 32005KT 3/8SM FG BKN020 OVC230 07/07 A2930 RMK FG6SC1CI1 SLP922

Example (8):

Celestial Dome, Example 8 (See long description below)
Description of image

The following Celestial Dome illustration provides an example with SC (4/8) based at 2000 feet, TCU (1/8) based at 2000 feet.

Observed: SC (4/8) based at 2000 feet, TCU (1/8) based at 2000 feet.

Reported: METAR CYOJ 012100Z 11012KT 15SM BKN020TCU 24/18 A3010 RMK TCU5 TCU NE SLP197

Example (9):

Celestial Dome, Example 9 (See long description below)
Description of image

The following Celestial Dome illustration provides an example with SC (2/8) based at 2000 feet, TCU (2/8) based at 2000 feet.

Observed: SC (2/8) based at 2000 feet, TCU (2/8) based at 2000 feet.

Reported: METAR CYXU 012000Z 21010KT 15SM SCT020TCU 27/22 A3008 RMK TCU4 SLP178

Example (10):

Celestial Dome, Example 10 (See long description below)
Description of image

The following Celestial Dome illustration provides an example with SF (1/8) based at 200 feet, BR (7/8) vertical visibility 400 feet.

Observed: SF (1/8) based at 200 feet, BR (7/8) vertical visibility 400 feet.

Reported: METAR CYGK 051700Z 10005KT 1SM BR FEW002 VV004 09/09 A3010 RMK SF1FG7 SLP197

Example (11):

Celestial Dome, Example 11 (See long description below)
Description of image

The following Celestial Dome illustration provides an example with ST (8/8) based at 1000 feet, AC (3/8) based at 8000 feet.

Observed: ST (8/8) based at 1000 feet, AC (3/8) based at 8000 feet

Reported: METAR CYOW 141800Z 18010KT 15SM OVC010 OVC080 22/20 A3010 RMK ST8AC3 SLP197

Example (12):

Celestial Dome, Example 12 (See long description below)
Description of image

The following Celestial Dome illustration provides an example with ST (4/8) based at 1200 feet, AC (5/8) based at 13 000 feet.

Observed: ST (4/8) based at 1200 feet, AS (5/8) based at 13 000 feet.

Reported: METAR CYZT 251300Z 14017KT 15SM SCT012 BKN130 07/06 A3012 RMK ST4AS5 SLP199

16.3.10 Temperature/dewpoint temperature (T’T’/T’dT’d)

The dry-bulb temperature and the dewpoint temperature shall be observed to the nearest tenth of a degree Celsius.

The air temperature and dewpoint temperature in the METAR shall be rounded to the nearest whole degree Celsius. Observed values involving 0.5°C shall be rounded up to the next highest (warmer) Celsius degree.

T'T': Dry-bulb temperature

T'dT'd: Dewpoint temperature

Example (1): Observed temperature of -9.5°C will be rounded to M09 in the METAR.

Example (2): Observed temperature of -0.1°C to -0.5°C will be rounded to M00 in the METAR.

16.3.11 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.

Example: A3012 would represent an altimeter setting of 30.12 inches of mercury.

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

Information on the existence of low level wind shear along the runway takeoff or approach path 1500 feet AGL and below that is considered significant to aircraft operations shall be reported.

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 reporting (see 16.3.7), 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.

16.3.13 Remarks (RMK)

The Remarks portion of the METAR observation is used to describe meteorological information of importance. Entries in Remarks are by no means restricted to the examples shown in this document. Directions in Remarks shall be recorded in a clockwise order.

Example: Prevailing visibility is 7 miles in light rain. Visibility to the east-southeast is reduced to 2 miles in mist.

METAR CYBX 111300Z 29008KT 7SM -RA OVC020 13/12 A2904 RMK SC8 VIS 2 E-SE BR SLP836

Remarks shall appear in the following order:

  1. Layer type and amount.
  2. General aviation remarks.
  3. MSL pressure (SLPppp).

16.3.13.1 Layer type and amount (oktas)

For each layer reported in the layer aloft section (see 16.3.9), a corresponding cloud (from the list below) and amount shall be recorded. When vertical visibility is observed, the obscuring phenomenon abbreviation and amount shall be recorded. The amount will be a single digit.

When surface based layers (see 1.2.5) are observed to obscure portions of the celestial dome, the obscuring phenomenon abbreviation and amount shall be recorded.

Table for clouds abbrivations and definitions
Clouds Abbreviations
Altocumulus AC
Altocumulus Castellanus ACC
Altostratus AS
Cirrocumulus CC
Cirrostratus CS
Cirrus CI
Cumulonimbus CB
Cumulus CU
Cumulus Fractus CF
Towering Cumulus TCU
Nimbostratus NS
Stratocumulus SC
Stratus ST
Stratus Fractus SF

Note: The cloud type described in the International Cloud Atlas as "Cumulus Congestus" is listed above as "Towering Cumulus....TCU".

Table for Obscuring Phenomena and its Abbreviations
Obscuring Phenomena Abbreviations
Rain (any form including SHRA and FZRA) RA
Hail GR
Ice Pellets (including Ice Pellet Showers) PL
Drizzle (including Freezing Drizzle) DZ
Ice Crystals IC
Snow (Snow Showers, Snow Pellets, Snow Grains) SN
Blowing Snow BLSN
Fog (any form) FG
Blowing Dust BLDU
Dust Storm DS
Haze HZ
Blowing Sand BLSA
Sandstorm SS
Smoke FU
Volcanic Ash VA

16.3.13.2 General aviation remarks

General aviation remarks will include remarks that are significant to aircraft operations. The observer should note that these Remarks will be disseminated globally and discretion should be used as to the content of the Remarks. MANAB (Manual of Word Abbreviations) abbreviations are to be used. Observers are encouraged to use the Remarks section and are not restricted to the examples over the next few pages.

16.3.13.2.1 Wind remarks
METAR…27040G55
...RMK… WSHFT 0850
METAR…05009
...RMK… WND ESTD DUE ICE ACCRETION
METAR…14015
...RMK… WND ESTD

If winds are estimated due to ice accretion, the remark shall be included in the report.

If winds are estimated for reasons other than ice accretion, the remark shall be included in the report.

16.3.13.2.2 Visibility remarks
METAR…1/2SM FG
…RMK… VIS VRB 1/4-3/4
METAR…4SM BR
…RMK… VIS VRB 2-6
METAR…10SM PRFG
…RMK… FG BANK W VIS 2
METAR…3/4SM BR
…RMK… VIS IMPRG 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 DRFTG OVR FLD VIS N 1
METAR…3/8SM
…RMK… RVR RWY 06R 1600FT
METAR…6SM -RA BR
…RMK… BCFG SE VIS 1/4
METAR…1/2SM FG
…RMK… PRFG SE-N
METAR…10SM BCFG
…RMK… BCFG SE QUAD VIS 1/2
METAR…10SM MIFG
…RMK… MIFG OVER APCH RWY 27
METAR…6SM
…RMK… SF8 FG BANK ALQDS
16.3.13.2.3 Weather remarks
METAR…OVC030CB 7SM +FC
…RMK… TORNADO SW MOVG E
METAR…BKN035TCU 8SM -SHRA
…RMK… FUNNEL CLOUD REPD 1435Z 15 S MOVG NE (1)  
METAR…BKN045CB 10SM TS
…RMK… CB W MOVG N (2)  
METAR…OVC040 8SM -RA
…RMK… -RA INTMT
METAR…OVC040 8SM
…RMK… INTMT -RA (3)
METAR…SCT035 10SM
…RMK… CB TOPS SW OCNL LTGIC SW (4)
METAR…SCT035 15SM
…RMK… OCNL -SHRA (5)
METAR…VV007 1/2SM SN
…RMK… SN WET  
METAR…BKN030 15SM
…RMK… VIRGA N  
METAR…BKN025CB 4SM TSRAGR
…RMK… HAIL DIAM nn MM (6)
METAR…SKC 25SM
…RMK… FROIN (7)
  1. If a tornado, waterspout or funnel cloud is reported by the public, indicate:
    1. the location with respect to the station, city or town;
    2. the direction towards which it is moving; and
    3. the time the phenomenon was observed.
  2. Observed cloud layer is combination of TCU and CB.
  3. Intermittent rain was not occurring at the time but was active within 15 minutes preceding the time of the observation.
  4. When lightning is observed, indicate frequency (OCNL, FRQ, CONTUS), type (LTGCG, LTGIC and LTGCC) and direction from station. CB not reported since base of observed CB clouds not visible. The following may be used as a guide for the frequency of lightning:
    1. OCNL less than one flash per minute
    2. FRQ one to six flashes per minute
    3. CONTUS more than six flashes/minute
  5. Rain showers were not occurring at the time but were active within 15 minutes preceding the time of the observation.
  6. When hail is observed at the station, the average size of the hail shall be estimated in whole millimetres, and recorded in Remarks. Where "nn" is the average diameter in whole millimetres.
  7. FROIN is used to report frost on the Ice Accretion Indicator.
16.3.13.2.4 Sky condition remarks

Sky cover

METAR…BKN070
…RMK… AC XTNDG RPDLY FM SW
METAR…OVC007
…RMK… OVC TPG HILLS NE
METAR…FEW250
…RMK… CONTRAILS (1)
  1. Shall be used when middle (CM) or high (CH) cloud consists in whole or in part of persistent (15 minutes or more) condensation trails. Rapidly dissipating condensation trails shall not be reported.

Ceiling

METAR…BKN008
…RMK… ACFT REPD CIG
METAR…OVC006
…RMK… CIG LWR SE
METAR…OVC003
…RMK… CIG DFUS VERT VIS 5
METAR…OVC000
…RMK… CIG 35 FT
METAR…OVC004
…RMK… BLN DSAPRD 550 FT
METAR…OVC007
…RMK… CIG VRB 5-9
METAR…VV002
…RMK… CIG VRB 1-3

Convective clouds

If clouds which indicate unstable conditions (CB, TCU or ACC) are observed, they shall be reported in Remarks.

METAR …BKN100
…RMK… AC6 ACC W
METAR …FEW040
…RMK… CB1 CB TOPS NW (1)
METAR …SCT030CB
…RMK… CB4 CB MOVG RPDLY FM SE
  1. If TCU or CB clouds base are not observed and not reported in the sky condition, they shallbe reported in Remarks.

Orographic clouds

When observed, orographic clouds, also known as standing wave clouds shall be reported in Remarks whether or not the clouds are predominant. These clouds sometimes indicate severe turbulence aloft and are normally seen in areas up to 350 km to the leeward of mountains or hills and may occur for a period of 5 or 6 hours or longer.

METAR …SCT040 SCT090
…RMK… SC3AC1 ACSL OVR RDG NW (1)
METAR …SCT060TCU
…RMK… TCU3 ROTOR CLDS NW  
  1. ACSL indicates standing lenticular altocumulus.
16.3.13.2.5 Pressure change remarks
METAR ...SCT040
…RMK… PRESRR   (1)
METAR …BKN100
…RMK… PRESFR   (2)
  1. PRESRR is used when the barograph trace indicates that the station pressure is rising at the rate of 2.0 hPa or more per hour.
  2. PRESFR is used when the barograph trace indicates that the station pressure is falling at the rate of 2.0 hPa or more per hour.

Note: If the barograph trace shows a steady increase of 0.5 hPa during the last 15 minutes, the rate of increase would be 2.0 hPa per hour and the remark PRESRR would be appropriate. If the barograph trace shows a steady decrease of 0.5 hPa during the last 15 minutes, the rate of decrease would be 2.0 hPa per hour and the remark PRESFR would be appropriate.

16.3.13.2.6 Snowfall remarks

The increasing depth of newly fallen snow, since the time of the last main synoptic report, shall be reported in the Remarks section of a METAR report by means of a /Sss/ group. The letter "S" identifies the precipitation as snow and "ss" the units as whole centimetres.

The accumulating depth of newly fallen snow, since the last main synoptic report, is normally obtained by ruler and rounded off to whole centimetres.

/Sss/ shall be reported only at the hours when the accumulated (rounded) value increases to equal or exceed 1cm, or exceeds the previously reported value by 1 cm or more.

This provides examples on how to properly code newly fallen snow in Remarks.
Time(UTC) Accumulated snowfall (cm) Recorded snowfall
0700 0.2 -
0800 1.4 /S01/
0900 3.2 /S03/
1000 3.8 /S04/
1100 4.4 -
1200 5.8 /S06/
1300 1.4 /S01/

Example: Observer reports 1 cm of newly fallen snow since the last main synoptic report.

METAR CYYQ 121500Z 30006KT 15SM -SN OVC007 M12/M14 A2956 RMK SC8 /S01/ SLP012

Note: If all the snow melts as it hits the ground, /Sss/ would not be reported.

16.3.13.2.7 Rainfall remarks

All sites equipped with a recording rain gauge, the standard type B rain gauge or the AWOS precipitation gauge shall report the accumulated rainfall, since the time of the last main synoptic report, in the Remarks section of the METAR observation by means of an /Rrr/ group.

The letter "R" identifies the precipitation as rain and the "rr" the units in whole millimetres. /Rrr/ is the accumulative rainfall, rounded off to the nearest whole millimetre.

/Rrr/ is the accumulative rainfall, rounded off to the nearest whole millimetre.

The /Rrr/ group shall be recorded and transmitted only at the hours when the rainfall 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.

This provides examples on how to properly code recorded rainfall in Remarks.
Time (UTC) Accumulated rainfall (mm) Recorded rainfall
0700 3.2 -
0800 9.8 /R10/
0900 20.2 /R20/
1000 29.7 /R30/
1100 39.1 -
1200 43.4 /R43/
1300 10.1 /R10/
16.3.13.2.8 Snowfall (or rainfall) reporting procedures for part-time stations

Part-time stations are defined as operating daily but fewer than 24 hours. When the station reopens, the first observation will indicate the reportable snowfall (or rainfall) amount, using the format /Sss AFT HH/ (or /Rrr AFT HH/), where HH is the hour (UTC) of the main synoptic at or prior to the time of closing.

If the closed period includes a main synoptic hour, and if the reopening time is at a non-synoptic hour, the second and subsequent snow (or rain) reports will take the form / Ss1s1 AFT H1H1UTC/, where the flag indicates that H1H1UTC is the time the station reopened and s1s1 is the snowfall (or rainfall) amount since the station reopened. Note that for rainfall, Ss1s1 is replaced by Rr1r1.

The following diagram shows three closing and opening situations. The reporting procedures for coding and reporting each situation is described below the diagrams.

Part-Time Stations Diagram (See long description below)
Description of image

This diagram illustrates three closing and opening situations for Part-Time Stations. Example 1: station opened from

Example (1): Opening time 1400 UTC (opening can be from 13 UTC to 17 UTC)

First report, use the format:
/Sss AFT 00UTC/ 
Subsequent reports, up to and including 18 UTC, use format
/Ss1s1 AFT 14UTC/ 

Example (2): Opening time 0000 UTC

First report, use the format:
/Sss AFT 06UTC/ 
Subsequent reports, use conventional format
/Sss/ 

Example (3): Opening time 0900 UTC (opening can be from 07 UTC to 11 UTC)

First report, use the format:
/Sss AFT 00UTC/ 
Subsequent reports, up to and including 12 UTC, use format
/Ss 1 s 1 AFT 09UTC/ 

Note: For rainfall, Sss is replaced by Rrr.

16.3.13.3 Late weather observations

In order that users of weather observations may have confidence in the observations and use them safely, it cannot be overstressed that hourly observations must be accurate and adhere to the schedules specified in Chapter 9. Every effort must be made to ensure that weather observations are taken on time. However, should an occasion arise, beyond the control of the observer, that necessitates taking the observation late (see 9.2.1 and 9.2.2), the following shall apply.

The number of minutes after the hour that the observation has been taken shall be entered as the first of the general weather remarks. 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 121300Z 00000KT 15SM FEW012 FEW220 M20/M22 A3039 RMK SC1CI1 OBS TAKEN +18 SLP308

16.3.13.4 Observational program status

In order that users of weather observations can determine if a station is staffed or when the next observation will be, Remarks indicating the status of operation are required.

At sites with less than a 24-hour observing program and observations not supplemented with an auto 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 10Z.

METAR CYGK 010300Z 20005KT 15SM SCT090 BKN110 21/17 A2994 RMK AC3AC2 LAST OBS/NEXT 011000UTC SLP138

At sites with a 24-hour program and a staff/machine mix for observations, enter 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

16.3.13.5 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.

Example: The MSL pressure is observed as 1002.9 hPa.

METAR CYWH 121500Z 00000KT 15SM FEW008 FEW020 BKN050 OVC120 09/08 A2962 RMK SF1SC2SC4AC2 SLP029

16.4 Types of observations

16.4.1

Observations are divided into two main types: METAR and SPECI. Synoptic observations are discussed in Part C.

16.4.2 Hourly observation

METAR observations are the observations taken to meet scheduled transmission times at the hour "H" during the period H-5 to H.

16.4.3 SPECI observation

A SPECI observation shall be taken and transmitted whenever one or more of the elements listed in 16.4.4 have changed in the amount specified. A SPECI should be transmitted within Time of SPECI +5 minutes. The amount of change is with reference to the preceding METAR or SPECI observation.

16.4.4 Criteria for taking SPECI

16.4.4.1 Ceiling

Ceiling decreases to less than or if below, increases to equal or exceed the following coded values of height:

  1. 15
  2. 10
  3. 5
  4. 4*
  5. 3
  6. 2*
  7. 1*
  8. The additional limit as specified in Appendix V entitled "IFR Approach and alternate limits for Canadian aerodromes."

Note: Criteria marked with an asterisk (*) are applicable only at aerodromes with approved precision approaches and only down to and including the lowest published minima for these aerodromes.

16.4.4.2 Obstruction to vision

SPECI shall be taken to report the beginning and ending of freezing fog.

16.4.4.3 Sky condition

A layer aloft is observed below

  1. 1000 feet and no layer aloft was reported below this height in the report immediately previous; or
  2. the highest minimum for IFR straight-in landing or take-off, and no layer was reported below this height in the report immediately previous.

Note: Under rapidly varying conditions of low ceiling and/or visibility, observers should, when possible, apply the provisions of 16.3.9.7 for the reporting of variation.

16.4.4.4 Visibility

Prevailing visibility decreases to less than or if below, increases to equal or exceed the following values:

  1. 3 miles
  2. 1 1/2 miles
  3. 1 mile
  4. 3/4 mile*
  5. 1/2 mile
  6. 1/4 mile*
  7. The additional limit as specified in Appendix V entitled "IFR Approach and alternate limits for Canadian aerodromes".

Note: Criteria marked with an asterisk (*) are applicable only at aerodromes with approved precision approaches and only down to and including the lowest published minima for these aerodromes.

16.4.4.5 Tornado, waterspout or funnel cloud

  1. Is observed
  2. Disappears from sight

16.4.4.6 Thunderstorm

  1. Begins
  2. Ends (SPECI observation shall be made when 15 minutes have elapsed without the occurrence of thunderstorm activity; see 3.3.3).

16.4.4.7 Precipitation

When any of the following begin, end or change intensity:

  • freezing rain
  • freezing drizzle
  • ice pellets (showery and non-showery)
  • rain
  • rain showers
  • drizzle
  • snow
  • snow showers
  • snow grains
  • hail
  • snow pellets
  • ice crystals

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

Changes in 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 of the precipitation.

Example:
-RA begins or -RA ends: SPECI is required
-RA changes to RA: SPECI is required
-RA changes to SHRA: SPECI is required
-RA changes to -SHRA: SPECI is not required
-RA changes to -RA INTMT: SPECI is not required

16.4.4.8 Temperature

  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.

Note: Stations where SPECI are required for temperature changes, as designated by NAV CANADA, are listed in Appendix II.

16.4.4.9 Wind

  1. Speed (two-minute mean) increases suddenly to at least double the previously reported value and exceeds 30 knots.
  2. Direction changes sufficiently to fulfill criteria required for a "wind shift" (see par. 7.1.4.1).

16.4.4.10 Volcanic eruption

The occurrence of a volcanic eruption shall be reported by a SPECI observation when 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 (SM) of the volcano.
  3. Date / Time (UTC) of eruption.
  4. Height and direction of movement of ash cloud.
  5. Other pertinent data.

Example: METAR ... RMK MT ST HELEN VOLCANO 60 MI WNW ERUPTED 091025 ASH CLOUD TO 300 MOVG RPDLY SE

Post-eruption volcanic ash clouds should be included in Remarks of METAR and SPECI observations as long as significant.

16.4.4.11 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 to take 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 will be transmitted as a SPECI.

  • A pilot report is received from an aircraft within 1 1/2 SM of the boundary of an airfield, and the PIREP indicates that weather conditions as observed by the pilot differ significantly from those reported by the current observation and when a pilot reports wind shear in the lower layers (see 16.3.12).
  • On request of a forecast centre, Air Traffic Controller (ATC).
  • Immediately upon learning of an aircraft accident, at or in the vicinity of the weather observing station. The observer shall issue an Accident Observation unless a complete METAR has issued made subsequent to the accident. The Accident Observation shall be as complete and accurate as possible, with particular care being taken to include in "Remarks" any meteorological facts that might relate to the accident, or which might be of significance to the aircraft accident investigator.
  • Observer's initiative.

16.4.4.12 Graphic reference guide for reporting a SPECI

Appendix I, graphic reference guide, may be used to assist in the identification of criteria for the issuance of special (SPECI) weather observations. Note that temperature criteria are only to be applied at sites specified by NAV CANADA.

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