MANAIR Manual of Standards and Procedures for Aviation Forecasts: chapter 5

Chapter 5 SIGMET Information

• 5.1 Definition
• 5.2 Domain
• 5.3 Projection
• 5.4 Language
• 5.5 Units
• 5.6 Types of SIGMET
• 5.7 Structure of the SIGMET message
• 5.8 Format of SIGMET

5.1 Definition

SIGMET: Information message issued by a meteorological watch office (MWO) to advise pilots of the occurrence or expected occurrence of specified weather phenomena, which may affect the safety of aircraft operations, and the development of those phenomena in time and space.

5.2 Domain

The message shall describe specified weather phenomena up to and including 60,000 feet (FL600) for the Canadian Flight Information Regions (FIR) and by international agreement, the Gander Oceanic flight information region. Refer to D.1 of Appendix D for the map of the Canadian SIGMET information domain.

5.3 Projection

As per the Technical Regulations, Volume II, Meteorological Service for International Air Navigation, section [C.3.3] 3.2.2 (WMO-No. 49), the depiction of the location of the phenomenon shall use the polar stereographic projection true at 60 degrees latitude north with lines between coordinate points as orthodromes (great circles).

5.4 Language

SIGMET messages are prepared in abbreviated English language using approved MSC abbreviations as published in Manual of Word Abbreviations (MANAB). Abbreviations and words to be used in SIGMET messages are given in D.2 of Appendix D.

5.5 Units

The only units explicitly stated are:

• nautical miles (NM) for a distance associated to the abbreviation WTN (within)
• knots (KT) for speed
• zulu (Z) for time in UTC, with midnight being indicated by the numerals zero and zero “00”
• Heights are stated in hundreds of feet and preceded by the abbreviation FL.

5.6 Types of SIGMET

Although ICAO Annex 3 provides one general SIGMET format, which encompasses all of the specified weather phenomena, it is convenient to distinguish between three types of SIGMET, as follows:

• WS SIGMET for TS, TURB, ICG, MTW, LLWS, DS, SS, RDOACT CLD
• WV SIGMET for volcanic ash (VA)
• WC SIGMET for tropical cyclones (TC)

The type of SIGMET can be identified through the data type designator included in the WMO abbreviated heading of the SIGMET message as explained in 5.7.

5.7 Structure of the SIGMET message

A SIGMET message consists of:

• WMO heading: all SIGMET are preceded by an appropriate WMO heading;
• First line: containing location indicators of the relevant ATS unit serving the FIR and MWO, alphanumeric identification and period of validity;
• Meteorological part: containing meteorological information concerning the phenomenon for which the SIGMET is issued; and
• Equal sign “=”: indicates the end of the message.

The first two parts of the SIGMET message are common for all SIGMET types. The content and format of the meteorological part is different depending on the type of SIGMET. Therefore, in the following paragraphs, the meteorological part of the WS, WV and WC types of SIGMET is described separately.

5.8 Format of SIGMET

5.8.1 WMO header

The Manual on the Global Telecommunication System (WMO-No. 386) recommends the use of the following abbreviated headings for bulletins containing meteorological information.

5.8.1.1 Data type designator

T₁: W for Warnings (WMO-No. 386, table A, A.II 5/2)

T₂: S for SIGMET (WMO-No. 386, table B1, A.II-5/6)

T₂: C for Tropical Cyclone (WC SIGMET)

T₂: V for Volcanic Ash (WV SIGMET)

5.8.1.2 Geographical designator

The geographic designator is where the meteorological information applies to, not the issuing country.

A₁A₂: CN for Canada (all FIRs but CZQX Oceanic) (WMO-No. 386, table C1, A.II-5/9)

A₁A₂: NT for North Atlantic area (CZQX Oceanic) (WMO-No. 386, table C1, A.II-5/12)

5.8.1.3 Bulletin number

ii: number with two digits

• 01-19 for global distribution
• 20-39 for inter-regional distribution (as per WMO regions)

5.8.1.4 International four-letter location indicator of the centre originating or compiling the bulletins

CCCC: As standardized practice, all SIGMET messages issued by Canada will be under CWAO which refers to the Canadian Meteorological Centre/Network Operations (CMC/NETOPS) as the centre compiling the bulletins.

5.8.1.5 Correction identifier

CCx: Since there are no provisions in ICAO documentation for correcting a SIGMET, the correction identifier will not be used. Refer to 5.8.6 for details.

5.8.1.6 Bulletin scheme

SIGMET messages will be issued in a set of two bulletins. The first one is aimed at international distribution while the second one will contain additional information for National purposes. Refer to D.3 of Appendix D for the full bulletin scheme.

5.8.2 First line--CCCC SIGMET [n]nn VALID YYGGgg/YYGGgg CCCC-

5.8.2.1 Daily alphanumeric sequence

1. A SIGMET message shall be identified by a letter:
   • Letter attribution rules and the lettering scheme are defined in D.4 of Appendix D.
2. A SIGMET message letter shall be numerically sequenced:
   • numbering of a SIGMET message (of the letter) begins at one;
   • the number is incremented by one when updating the message, including cancellation;
   • the sequence number shall correspond with the number of SIGMET messages issued for an event within a FIR since 0000Z on the day concerned; and
   • the numbering is thus reset at 0000Z (messages are not updated at 0000Z for the sole purpose of resetting the number).

Figure 3: Diagram of numeric sequence of SIGMET messages.

Example: CZUL SIGMET M3 VALID 161220/161620 CWUL-

5.8.2.2 Validity period and lead time of SIGMET

1. The period of validity of a WS SIGMET is four hours.
2. The period of validity of a WV SIGMET and a WC SIGMET is six hours.
3. In the case of a SIGMET for an ongoing phenomenon:
   • the date/time group indicating the start of the SIGMET period will be rounded back to five minutes from the filing time (date/time group in the WMO heading).
4. In the case of a SIGMET for an expected phenomenon:
   • The beginning of the validity period will be the time of the expected commencement (occurrence) of the phenomenon.
   • For a WS SIGMET, the lead time (the time of issuance of the SIGMET) can be up to four hours before the start of the validity period (i.e. expected time of occurrence of the phenomenon).
   • For a WV SIGMET and a WC SIGMET, the lead time can be up to 12 hours before the start of the validity period.
   • A SIGMET for an expected phenomenon is issued only for the first appearance of an event in Canadian airspace (i.e. moving in from the U.S. or onset inside a Canadian FIR). A phenomenon moving from one FIR to another is treated as an ongoing phenomenon. No forecast event SIGMET messages would be sent for the second FIR.

Example (1): For an ongoing phenomenon:

WSCN05 CWAO 161220
CZUL SIGMET M3 VALID 161220/161620 CWUL-

Example (2): For an expected phenomenon (expected time of occurrence 0315Z):

WSCN01 CWAO 040115
CZVR SIGMET U1 VALID 040315/040715 CWEG-

5.8.2.3 Meteorological Watch Office (MWO)

• CWUL for Canadian Meteorological Aviation Center East (CMAC-E) in Montréal.
• CWEG for Canadian Meteorological Aviation Center West (CMAC-W) in Edmonton.

5.8.3 Format of the meteorological part of a WS SIGMET

The meteorological part of a WS SIGMET consists of nine elements identified in the following table (this table has been divided into two parts due to horizontal space constraints):

5.8.3.1 Location indicator and name of the FIR (element 1 and 2)

Example (1): CZUL MONTREAL FIR

Example (2): CZVR VANCOUVER FIR

5.8.3.2 Description of the phenomenon (element 3)

The description of the phenomenon consists of a qualifier and a phenomenon abbreviation. SIGMET will be issued for the following phenomena (with only one phenomenon in each SIGMET):

• Thunderstorm (TS): FRQ or SQLN, with hail, tornado/waterspout as necessary
• Turbulence (TURB): only SEV
• Icing (ICG): only SEV with or without FZRA
• Mountain waves (MTW): only SEV
• Low Level wind shear (LLWS)
• Dust storm (DS): only HVY
• Sand storm (SS): only HVY
• Radioactive cloud: RDOACT CLD¹

The appropriate abbreviations and combinations thereof, and their meaning are given in D.5 of Appendix D.

5.8.3.3 Indication if the phenomenon is observed or forecast (element 4)

OBS [AT <GGggZ>] or FCST

The use of “OBS” occurs if either:

• there has been a recent¹ direct observation of the phenomenon (i.e. METAR, PIREP); or
• there has been a recent¹ indirect observation of the phenomena (i.e. remote sensing imagery) or the observation of a meteorological element (i.e. strong wind, freezing precipitation), which leads the forecaster to believe that the phenomenon is occurring.

The code OBS is optionally followed by the time group in the form AT GGggZ, where GGgg is the time of the observation in hours and minutes UTC. If the exact time of the observation is not known the time is not included. No additional information will be given, i.e. aircraft type reporting the phenomenon.

The use of “FCST” occurs if either:

• the phenomenon is not directly or indirectly observed but there is strong meteorological evidence (i.e. numerical guidance) to suggest that the phenomenon is occurring; or
• there is an expected phenomenon. In other words, there is meteorological evidence (i.e. numerical guidance) to suggest that the phenomenon will be occurring within the prescribed lead time (refer to 5.8.2.2).

When FCST is used, it is assumed that the time of the occurrence or commencement of the phenomenon coincides with the beginning of the period of validity in the first line of the SIGMET.

Example (1): OBS AT 0140Z

Example (2): FCST

5.8.3.4 Location of the phenomenon (element 5)

The location of the phenomenon is depicted as an area using coordinate points:

• the description always begins with the abbreviation WTN (within);
• the area can be described as a circle, a line or a polygon; and
• distances are in nautical miles (NM), direction to one of the eight points of compass (octants¹).

Coordinate points:

1. The international (ICAO) SIGMET message describes a coordinate point using a latitude and longitude only (resolution defined in D.6 of Appendix D).
2. The national SIGMET message describes a coordinate point using a latitude and longitude. Additionally, an equivalent description with respect to an aviation reference site³ is given and is an approximation of the coordinate point in latitude and longitude.

There are two exceptions to this rule:

1. Any coordinate point located within Gander Oceanic FIR will be described in latitude and longitude only. These points will be limited to the resolution as defined in D.6 of Appendix D.
2. Any coordinate point north of N72°00’ will be described with respect to an aviation reference site only if within a 90 nautical mile radius of that site. Otherwise the coordinate point will be represented in latitude and longitude only. This is due to the sparse number of aviation reference sites over northern Canada.

5.8.3.5 Flight level and extent (element 6)

FL<nnn/nnn>
SFC/FL<nnn>
TOP FL<nnn>

The location and extent of the phenomenon in the vertical is given by one or more of the above abbreviations, as follows:

• Reporting a layer “FL<nnn/nnn>”, where the lower level is reported first; this is used particularly in reporting turbulence and icing
• Reporting a layer with reference to one FL using “SFC/”
• Reporting the level of the tops of the TS clouds using the abbreviation “TOP”

Example (1): SEV TURB…FL220/270

Example (2): SEV ICG (FZRA)…SFC/FL030

Example (3): FRQ TS…TOP FL340

5.8.3.6 Movement or expected movement (element 7)

MOV <direction, speed>KT or QS

Direction of movement is given with reference to one of the sixteen points of compass (radials¹). Speed is given in knots (KT). The abbreviation QS is used if no significant movement is expected.

Example: MOV SSE 15KT

5.8.3.7 Change in intensity (element 8)

The expected evolution of the phenomenon’s intensity is indicated by one of the following abbreviations:

• INTSFYG: intensifying
• WKNG: weakening
• NC: no change

5.8.3.8 Remark (element 9)

The remark (RMK) is found only in the National SIGMET message. It begins on a new line. The purpose is to allow additional information of national interest to be conveyed in the SIGMET message. Items listed in the remark line will be separated by a forward slash (/).

• The GFA region(s) the SIGMET message applies to (refer to Figure 4)
• Cross-referencing SIGMET messages when a phenomenon straddles one or several FIR boundaries (refer to Figure 4)
• For a phenomenon that has moved out of an FIR, the cancelled SIGMET message will refer to the continuing SIGMET message in neighbouring FIR(s) within Canada’s Area of Responsibility (AOR), (refer to Figure 5)

Symbolic form

RMK [GFACN<nn>] / [CCCC <name> FIR SIGMET[n]nn]¹

Figure 4: SIGMET phenomenon covering two FIR

The above phenomenon requires two SIGMET messages, one per FIR. The description will be identical in both messages (1) and (2) below:

Message (1):

WSCN22 CWAO 161220
CZEG SIGMET B1 VALID 161220/161620 CWEG-
CZEG EDMONTON FIR «meteorological part»
RMK GFACN32/CZWG WINNIPEG FIR SIGMET A1=

Message (2)

WSCN23 CWAO 161220
CZWG SIGMET A1 VALID 161220/161620 CWEG-
CZWG WINNIPEG FIR «meteorological part»
RMK GFACN32/CZEG EDMONTON FIR SIGMET B1=

Figure 5: SIGMET phenomenon now within only one FIR

The above phenomenon is a continuation of Figure 4. In other words, the area has moved southeastward with time. SIGMET A2 is an update of A1 while SIGMET B2 is a cancellation of B1 since the phenomenon no longer affects the Edmonton FIR. The messages would look like this:

Message (1):

WSCN22 CWAO 161530
CZEG SIGMET B2 VALID 1615300/161620 CWEG-
CZEG EDMONTON FIR CNCL SIGMET B1 161220/161620
RMK GFACN32/CZWG WINNIPEG FIR SIGMET A2=

Message (2):

WSCN23 CWAO 161530
CZWG SIGMET A2 VALID 161530/161930 CWEG-
CZWG WINNIPEG FIR «meteorological part»
RMK GFACN32=

5.8.3.9 RDOACT CLD event with limited information

In the case of a RDOACT CLD event and that limited information is available to the forecaster (i.e. first issuance of a RDOACT CLD SIGMET), the following elements may be set as ‘’UNKNOWN’’:

• Level unknown (element 6): FL UNKNOWN
• Movement unknown (element 7): MOV UNKNOWN
• Change in intensity unknown (element 8): INTSTY UNKNOWN

Example (1):

WSCN04 CWAO 161220
CZYZ SIGMET R1 VALID 161220/161620 CWUL-
CZYZ TORONTO FIR RDOACT CLD OBS AT 1205Z WTN 10 NM OF N4350 W07905
FL UNKNOWN MOV UNKNOWN INTSTY UNKNOWN=

Example (2):

WSCN24 CWAO 161220
CZYZ SIGMET R1 VALID 161220/161620 CWUL-
CZYZ TORONTO FIR RDOACT CLD OBS AT 1205Z WTN 10 NM OF /N4350 W07905/25 E CYYZ FL UNKNOWN MOV UNKNOWN INTSTY UNKNOWN
RMK GFACN33=

5.8.4 Format of the meteorological part of a WV SIGMET

The meteorological part of a WV SIGMET consists of the eight elements identified in the following table (this table has been divided into three parts due to horizontal space constraints):

5.8.4.1 Location indicator and name of the FIR (element 1 and 2)

Refer to 5.8.3.1.

5.8.4.2 Information on the volcano eruption (element 3)

VA ERUPTION [<name>] [PSN<Nnnnn Wnnnnn>]

• The name of the volcano is preceded by the words VA ERUPTION.
• The position of the volcano is given by the abbreviation PSN followed by the latitude and longitude in degrees and minutes (Nnnnn Wnnnnn).
• If the FIR is affected by a VA cloud with limited information about the eruption which generated the cloud, then parts of element 3 may be set as “unknown” (refer to 5.8.4.9 for details).

Example: VA ERUPTION GARIBALDI PSN N4951 W12300

5.8.4.3 Volcanic ash cloud (element 4)

VA CLD OBS AT <GGggZ> or VA CLD FCST

Time of observation of the VA CLD. The time of observation is taken from the source of the observation (satellite image, special air-report, report from ground volcano logical station, etc.). If the VA cloud is not yet observed over the FIR but the volcanic ash advisory received from the responsible VAAC indicates that the cloud will be affecting the FIR after a certain time within the next 12 hours, a SIGMET shall be issued, and the abbreviation VA CLD FCST shall be used.

Example (1): VA CLD OBS AT 0110Z

Example (2): VA CLD FCST

5.8.4.4 Extent of the cloud (element 5)

Vertical: Refer to 5.8.3.5.

Horizontal: Refer to 5.8.3.4.

5.8.4.5 Movement or expected movement (element 6)

Refer to 5.8.3.6.

Square brackets indicate that element 6 is optional. Given parts of a VA cloud may have differing motion (speed and direction) this element is omitted. Movement of the VA cloud is indicated by the forecast position at the end of the period of validity (element 7).

If at the end of the period of validity the VA cloud is expected to have left entirely Canada’s area of responsibility, then element 6 is used while element 7 is omitted.

5.8.4.6 Volcanic ash cloud forecast at the end of the period of validity (element 7)

FCST <GGggZ>

The “GGggZ” group should indicate the end of the validity period given in the first line of the SIGMET message.

Geographical location of the phenomenon as per 5.8.3.4. This is always preceded by the abbreviations VA CLD APRX.

Square brackets indicate that element 7 is optional. Specifically, if at the end of the period of validity the VA cloud is expected to have left Canada’s area of responsibility entirely, then element 7 is omitted and element 6 is used.

5.8.4.7 Remark (element 8)

Refer to 5.8.3.8

5.8.4.8 Example of a WV SIGMET

Example:

WVCN01 CWAO 111155
CZVR SIGMET S1 VALID 111200/111800 CWEG-
CZVR VANCOUVER FIR VA ERUPTION KASATOCHI PSN N5210 W17530
VA CLD OBS AT 1200Z FL270/400 WTN 30NM OF LINE N5415 W13502 -
N5045 W13255MOV E 5KT FCST 1800Z VA CLD APRX WTN 30NM OF LINE
N5415 W13411 - N5156 W13213 - N4956 W13100=

5.8.4.9 Special case: VA event with limited information

In the case of a VA cloud event and that limited information is available to the forecaster (i.e. first issuance of a VA SIGMET), the following elements may be set as “unknown’’:

• Eruption unknown (element 3): VA ERUPTION UNKNOWN PSN UNKNOWN
• Extent of the cloud unknown (element 5): FL UNKNOWN WTN UNKNOWN
• Movement unknown (element 6): MOV UNKNOWN

Example:

Eruption of Mount Garibaldi observed on satellite pictures, no AIREP and no volcanic ash advisory from Montréal VAAC.

WVCN01 CWAO 161220
CZVR SIGMET U1 VALID 161220/161820 CWEG-
CZVR VANCOUVER FIR VA ERUPTION GARIBALDI PSN N4951 W12300
VA CLD OBS AT 1205Z FL UNKNOWN WTN 60 NM OF N4951 W12300
MOV UNKNOWN =

5.8.5 Format of the meteorological part of a WC SIGMET

The meteorological part of a WC SIGMET consists of the 11 elements identified in the following table (this table has been divided into three parts due to horizontal space constraints):

5.8.5.1 Location indicator and name of the FIR (element 1 and 2)

Refer to 5.8.3.1.

5.8.5.2 Phenomenon and name (element 3)

TC <name>

The description of the tropical cyclone consists of the abbreviation “TC” followed by the international name of the tropical cyclone given by the Tropical Cyclone Advisory Centre (TCAC).

Example: TC GLORIA

5.8.5.3 Indication if the phenomenon is observed or forecast (element 4)

OBS [AT <GGggz>] or FCST

Refer to 5.8.3.3 Normally, time is taken from the forecaster’s observations or from a TC advisory received from a Tropical Cyclone Advisory Centre (TCAC) such as the Canadian Hurricane Centre (CHC). If the TC is not yet observed in the FIR but the tropical cyclone advisory or TC forecast indicate that the TC is going to affect the FIR within the next 12 hours, a SIGMET may be issued in which case the abbreviation FCST shall be used.

5.8.5.4 Location of TC centre (element 5)

Refer to 5.8.3.4.

5.8.5.5 Vertical/horizontal extent of CB cloud formation around the TC centre (element 6 and 7)

CB TOP FL<nnn> WTN <nnnNM> OF CENTRE

Example: CB TOP FL450 WTN 200NM OF CENTRE

5.8.5.6 Movement or expected movement (element 8)

Refer to 5.8.3.6.

5.8.5.7 Change in intensity (element 9)

Refer to 5.8.3.7.

5.8.5.8 Forecast position of centre at the end of the period of validity (element 10)

FCST <GGggZ>

The GGggZ group should indicate the end of the validity period given in the first line of the SIGMET message.

The geographical location of the TC centre is as per 5.8.3.4. This is always preceded by the abbreviations “TC CENTRE”.

Square brackets indicate that element 10 is optional. If at the end of the period of validity the area described in the SIGMET is expected to have left entirely Canada’s area of responsibility, then element 10 is omitted.

Example:

WCNT01 CWAO 1612220
CZQX SIGMET U2 VALID 161220/161820 CWUL-
CZQX GANDER OCEANIC FIR TC OLIVIA OBS AT 1200Z N4730 W03300
CB TOP FL360 WTN 120NM OF CENTRE MOV NE 25KT WKNG=

5.8.5.9 Remark (element 11)

Refer to 5.8.3.8.

5.8.5.10 Example of a WC SIGMET

Example: Tropical cyclone Bertha with centre inside Gander Oceanic FIR at N45º45’ W041º30’.

WCNT01 CWAO 1612220
CZQX SIGMET W3 VALID 161220/161820 CWUL-
CZQX GANDER OCEANIC FIR TC BERTHA OBS AT 1200Z N4545 W04130
CB TOP FL380 WTN 150NM OF CENTRE MOV NE 20KT WKNG
FCST 1820Z TC CENTRE N5230 W03430=

5.8.6 Correcting a SIGMET

In the event of a SIGMET message transmitted with an error, a correction is sent by updating the SIGMET according to 5.8.7.

5.8.7 Updating a SIGMET

An updated SIGMET, when issued, automatically replaces the previous SIGMET in the same series (i.e. the previous SIGMET with the same letter):

• A WS SIGMET must be updated every four hours (from date/time group in the WMO heading. (Refer to 5.8.1).
• A WV and a WC SIGMET must be updated every six hours (from date/time group in the WMO heading). (Refer to 5.8.1)
• However, a forecaster may update a SIGMET at any time if it is considered necessary.

For rules regarding the alphanumeric sequence, refer to 5.8.2.1.

Example (1): For an ongoing phenomena:

WSCN05 CWAO 161220
CZUL SIGMET M3 VALID 161220/161620 CWUL-

Updated four hours later (i.e. before 1620Z) as:

WSCN05 CWAO 161605
CZUL SIGMET M4 VALID 161605/162005 CWUL-

Example (2): For an expected phenomenon (expected time of occurrence 0315Z):

WSCN01 CWAO 040115
CZVR SIGMET U1 VALID 040315/040715 CWEG-

Updated at 0245Z as event occurred earlier (30 minutes) than expected:

WSCN01 CWAO 040245
CZVR SIGMET U2 VALID 040245/040645 CWEG-

Example (3): For an expected VA event (expected time of occurrence 1800Z):

WVCN02 CWAO 280920
CZEG SIGMET J1 VALID 281800/290000 CWEG-

Updated six hours later (i.e. before 1520Z) as:

WVCN02 CWAO 281510
CZEG SIGMET J2 VALID 281800/290000 CWEG-

Updated by the forecaster at the start of the occurrence as:

WVCN02 CWAO 281800
CZEG SIGMET J3 VALID 281800/290000 CWEG-

5.8.8 Cancelling a SIGMET

If, during the validity period of a SIGMET, the phenomenon for which the SIGMET had been issued is no longer occurring or no longer expected to occur, this SIGMET shall be cancelled by the issuing MWO. The cancellation is done by issuing the same type of SIGMET.

5.8.8.1 WMO header

Same data type designator. Refer to 5.8.1.

5.8.8.2 First line--CCCC SIGMET [n]nn VALID YYGGgg/YYGGgg CCCC-

5.8.8.2.1 Daily alphanumeric sequence

Number incremented by one. Refer to 5.8.2.1 for details.

5.8.8.2.2 Validity period of SIGMET

In the case of a SIGMET for an ongoing phenomenon:

• the date/time group indicating the start of the SIGMET period will be rounded back to five minutes from the filing time (date/time group in the WMO heading) while the date/time group indicating the end of the SIGMET period remains the same (as the SIGMET it cancels).
• if the validity period has expired, the date/time group indicating the start and end of the SIGMET period will all be the same, and those will be rounded back to five minutes from the filling time.

In the case of a SIGMET for an expected phenomenon:

• the validity period remains unchanged.

5.8.8.3 Second line

The second line of a cancelled SIGMET consists of seven elements identified in the following table (this table has been divided into two parts due to horizontal space constraints):

5.8.8.3.1 Location indicator and name of the FIR (element 1 and 2)

Refer to 5.8.3.1.

5.8.8.3.2 Cancellation (element 3)

Indicated by the abbreviation CNCL.

5.8.8.3.3 SIGMET message being cancelled (element 4)

The abbreviation SIGMET followed by the alphanumeric sequence of the message being cancelled.

5.8.8.3.4 Validity period of SIGMET message being cancelled (element 5)

A reference to the valid period for the SIGMET being cancelled.

5.8.8.3.5 VA movement (element 6)

Indication of VA moving into another FIR (optional). Coordination with neighbouring meteorological watch offices (MWO) is required if VA is moving into a FIR outside Canada’s area of responsibility.

5.8.8.3.6 Remark (element 7)

Refer to 5.8.3.8.

Example (1): For an ongoing phenomena:

WSCN05 CWAO 161220
CZUL SIGMET M3 VALID 161220/161620 CWUL-
CZUL MONTREAL FIR <<meteorological part>>
Cancelled as:
WSCN05 CWAO 161430
CZUL SIGMET M4 VALID 161430/161620 CWUL-
CZUL MONTREAL FIR CNCL SIGMET M3 161220/161620=

Example (2): For an ongoing phenomena:

WSCN05 CWAO 161220
CZUL SIGMET M3 VALID 161220/161620 CWUL-
CZUL MONTREAL FIR <<meteorological part>>
Cancelled late as the validity period had expired:
WSCN05 CWAO 161630
CZUL SIGMET M4 VALID 161630/161630 CWUL-
CZUL MONTREAL FIR CNCL SIGMET M3 161220/161620=

Example (3): For an expected phenomenon (expected time of occurrence 1500Z):

WSCN05 CWAO 161220
CZUL SIGMET M1 VALID 161500/161900 CWUL-
CZUL MONTREAL FIR <<meteorological part>>
Cancelled before the expected time of commencement of the phenomenon as:
WSCN05 CWAO 161430
CZUL SIGMET M2 VALID 161500/161900 CWUL-
CZUL MONTREAL FIR CNCL SIGMET M1 161500/161900=

5.8.9 Test SIGMET

There may be occasions when test SIGMET messages are transmitted by the MWO. The test SIGMET messages will be identifiable by the letter “T” in the alphanumeric sequence (refer to 5.8.2.1). Additionally, the statement “THIS IS A TEST” will be added at the beginning and end of the message.

Examples of a test message:

International (ICAO)

WSCN03 CWAO 162225
CZWG SIGMET T1 VALID 162225/170225 CWEG-
CZWG WINNIPEG FIR THIS IS A TEST SQLN TS OBS WTN 20NM OF LINE N4929 W09449 - N5104 W09348 - N5209 W09120 TOP FL340 MOV E 15KT NC THIS IS A TEST=

National

WSCN23 CWAO 162225
CZWG SIGMET T1 VALID 162225/170225 CWEG-
CZWG WINNIPEG FIR THIS IS A TEST SQLN TS OBS WTN 20NM OF LINE /N4929 W09449/25 SW CYQK - /N5104 W09348/CYRL  - /N5209 W09120/60 NW CYPL TOP FL340 MOV E 15KT NC THIS IS A TEST
RMK GFACN33=

Examples of a cancellation of test message:

International (ICAO)

WSCN03 CWAO 162300
CZWG SIGMET T2 VALID 162300/170225 CWEG-
CZWG WINNIPEG FIR THIS IS A TEST CNCL SIGMET T1 162225/170225 THIS IS A TEST=

National

WSCN23 CWAO 162300
CZWG SIGMET T2 VALID 162300/170225 CWEG-
CZWG WINNIPEG FIR THIS IS A TEST CNCL SIGMET T1 162225/170225 THIS IS A TEST
RMK GFACN33=

5.8.10 Relationship to GFA and Sig Wx prognostic charts

A SIGMET will be issued to advise pilots of the occurrence or expected occurrence of specified weather phenomena, regardless of the fact that the phenomena may or may not be included in the Graphic Area Forecasts (GFA). Once issued, a SIGMET message automatically amends the current GFA. Because a SIGMET may be covering a greater vertical extent than the GFA, it may also amend the Sig Wx prognostic charts.

5.8.11 Relationship to AIRMET

A SIGMET is always issued for its specified weather phenomena. On the other hand, an AIRMET is issued for its specified weather phenomena if not included in the GFA.

In a situation where a phenomenon described in a SIGMET decreases in intensity to now meet the AIRMET criteria (e.g. SEV TURB becomes MDT TURB), the SIGMET shall then be cancelled. An AIRMET shall be issued, if and only if the phenomenon was not forecast in the current GFA. If the phenomenon was forecast in the currently valid GFA, the issuance of an AIRMET is not required.

Conversely, a phenomenon that had resulted in the issuance of an AIRMET may increase in intensity to the SIGMET criteria. In this situation, the AIRMET shall be cancelled while a SIGMET shall be issued.