MET.TR.250 SIGMET

AIRSPACE In cases where the airspace is divided into a flight information region (FIR) and an upper-flight information region (UIR), the SIGMET should be identified by the location indicator of the ATS unit serving the FIR.

SIGMET — CODE FORM SIGMET, and cancellations thereof, should be encoded using:

(a)the IWXXM GML form as specified in point (a) of AMC1 MET.TR.115(a);

(b)abbreviated plain language as specified in point (c) of AMC1 MET.TR.115(a).

FORMAT SIGMET, when issued in graphical format, should be as specified below:

(a)SIGMET FOR TROPICAL CYCLONE — MODEL STC [Figure or form omitted from this preview — available in the Avioverse workspace library.]

(b)SIGMET FOR VOLCANIC ASH — MODEL SVA, MERCATOR PROJECTION [Figure or form omitted from this preview — available in the Avioverse workspace library.]

(c)SIGMET FOR VOLCANIC ASH — MODEL SVA, POLAR STEREOGRAPHIC PROJECTION [Figure or form omitted from this preview — available in the Avioverse workspace library.]

(d)SIGMET FOR PHENOMENA OTHER THAN TROPICAL CYCLONES AND VOLCANIC ASH — MODEL SGE [Figure or form omitted from this preview — available in the Avioverse workspace library.]

COORDINATION WITH NEIGHBOURING METEOROLOGICAL WATCH OFFICES (MWOs) An MWO should coordinate SIGMET with neighbouring MWO(s), especially when the en-route weather phenomenon extends or is expected to extend beyond the MWO’s specified area of responsibility, to ensure harmonised SIGMET provision.

FLIGHT INFORMATION REGION The SIGMET applies to the whole airspace within the lateral limits of the FIR, i.e. to the FIR and to the UIR. The particular areas and/or flight levels affected by the meteorological phenomena causing the issuance of the SIGMET are given in the text of the message.

EXAMPLE OF SIGMET, AND THE CORRESPONDING CANCELLATIONS

EXAMPLE OF SIGMET FOR TROPICAL CYCLONE

EXAMPLE OF SIGMET FOR VOLCANIC ASH

EXAMPLE OF SIGMET FOR RADIOACTIVE CLOUD

EXAMPLE OF SIGMET FOR SEVERE TURBULENCE

COORDINATION WITH NEIGHBOURING METEOROLOGICAL WATCH OFFICES (MWOs) Guidance on the bilateral or multilateral coordination between MWOs of neighbouring States for the provision of SIGMET can be found in ICAO EUR Doc 014 ‘EUR SIGMET and AIRMET Guide’.

SEQUENCE NUMBER

(a)The three-character sequence number should be constructed using a single letter identifying the phenomenon, followed by two numeric characters corresponding to the number of SIGMET issued for that phenomenon for the specified flight information region since 00.01 UTC on the day concerned.

(b)The letters to be used as the first character for the SIGMET sequence number to indicate the specified en-route weather and other phenomena for which the SIGMET has been issued should be:

(c)When SIGMET is issued for test purposes (‘TEST’ status indicator used in the SIGMET), then the appropriate letter for exchange test purposes should be used, i.e. ‘Y’ for a TEST volcanic ash SIGMET. When SIGMET is issued for exercise purposes (‘EXER’ status indicator used in the SIGMET), then the letter chosen should correspond to that used under normal circumstances, i.e. ‘A’ for a SIGMET issued during a volcanic ash exercise.

CRITERIA RELATED TO PHENOMENA Sandstorm/dust storm should be considered:

(a)heavy whenever the visibility is below 200 m and the sky is obscured; and

(b)moderate whenever the visibility is:

(1)below 200 m and the sky is not obscured; or

(2)between 200 and 600 m.

CRITERIA RELATED TO PHENOMENA

(a)An area of thunderstorms and cumulonimbus clouds is considered:

(1)obscured (OBSC) if it is obscured by haze or smoke or cannot be readily seen due to darkness;

(2)embedded (EMBD) if it is embedded within cloud layers and cannot be readily recognised;

(3)isolated (ISOL) if it consists of individual features which affect, or are forecast to affect, an area with a maximum spatial coverage less than 50 % of the area concerned (at a fixed time or during the period of validity); and

(4)occasional (OCNL) if it consists of well-separated features which affect, or are forecast to affect, an area with a maximum spatial coverage between 50 and 75 % of the area concerned (at a fixed time or during the period of validity).

(b)An area of thunderstorms is considered frequent (FRQ) if within that area there is little or no separation between adjacent thunderstorms with a maximum spatial coverage greater than 75 % of the area affected, or forecast to be affected, by the phenomenon (at a fixed time or during the period of validity).

(c)Squall line (SQL) indicates a thunderstorm along a line with little or no space between individual clouds.

(d)Hail (GR) is used as a further description of the thunderstorm, as necessary.

(e)Severe and moderate turbulence (TURB) refers only to: low-level turbulence associated with strong surface winds; rotor streaming; or turbulence whether in cloud or not (CAT). Turbulence is not used in connection with convective clouds.

(f)Turbulence is considered:

(1)severe whenever the peak value of the EDR equals or exceeds 0.45; and

(2)moderate whenever the peak value of the EDR is equal to or above 0.20 and below 0.45.

(g)Severe and moderate icing (ICE) refers to icing in other than convective clouds. Freezing rain (FZRA) should refer to severe icing conditions caused by freezing rain.

(h)A mountain wave (MTW) is considered:

(1)severe whenever an accompanying downdraft of 600 ft/min (3.0 m/s) or more and/or severe turbulence is observed or forecast; and

(2)moderate whenever an accompanying downdraft of 350–600 ft/min (1.75–3.0 m/s) and/or moderate turbulence is observed or forecast.