SIGMETs are issued to provide urgent advice to aircraft of actual or expected weather developments or trends that are potentially hazardous. SIGMETs are issued to advise of the occurrence or expected occurrence of the following phenomena: Code and Description OBSC TS - Obscured thunderstorm(s) EMBD TS - Frequent thunderstorm(s) SQL TS - Squall line thunderstorms OBSC TSGR - Obscured thunderstorm(s) with hail EMBD TSGR - Embedded thunderstorm(s) with hail FRQ TSGR - Frequent thunderstorm(s) with hail SQL TSGR - Squall line thunderstorms with hail TC - Tropical cyclone SEV TURB - Severe Turbulence SEV ICE - Severe icing SEV ICE FZRA - Severe icing due to freezing rain SEV MTW - Severe mountain wave HVY DS - Heavy duststorm HVY SS - Heavy sandstorm VA - Volcanic ash RDOACT CLD - Radioactive Cloud Pilots in command of aircraft encountering any of the above phenomena not notified by SIGMET advices must report details of the phenomena in an AIREP SPECIAL. SIGMET for thunderstorms are only issued when they are: obscured (OBSC) by haze or smoke embedded (EMBD) within cloud layers frequent (FRQ), i.e. with little or no separation between clouds and covering more than 75% of the area affected squall line (SQL) thunderstorms along a line of about 100 nautical miles or more in length, with little or no separation between clouds SIGMET for thunderstorms and tropical cyclones do not include reference to icing and turbulence as these are implied as occurring with thunderstorms and tropical cyclones. Responsibility for the issuance of SIGMET within Australian FIRs SIGMETs for volcanic ash are the responsibility of the Volcanic Ash Advisory Centre, Darwin. SIGMETs for tropical cyclones are the responsibility of the Tropical Cyclone Advisory Centres in Perth, Darwin and Brisbane. SIGMETs for turbulence and icing above FL185 are the responsibility of the Aviation Weather Centre, Melbourne. SIGMET for all other phenomenon are the responsibility of the Meteorological Watch Offices located in Perth, Darwin, Adelaide, Hobart, Melbourne, Sydney, Brisbane and Townsville. SIGMET Structure Bulletin Identification WCAU01 for SIGMET on tropical cyclones WVAU01 for SIGMET on volcanic ash cloud WSAU21 for SIGMET for other phenomena Originating Office (WMO Indicator) The World Meteorological Organisation (WMO) location indicators for Australian Meteorological Watch Offices are: APRM - Adelaide Regional Forecasting Centre APRF - Perth Regional Forecasting Centre ABRF - Brisbane Regional Forecasting Centre ASRF - Sydney Regional Forecasting Centre ADRM - Darwin Regional Forecasting Centre AMRF - Melbourne Regional Forecasting Centre AMHF - Hobart Regional Forecasting Centre ABTL - Townsville Meteorological Office AMMC - Melbourne Aviation Weather Centre Note: These differ from the ICAO indicators (beginning with Y) used elsewhere in the message. Issue Date/Time Issue date/time is given in UTC in the form DDHHMM, where DD is day of month, and HHMM is time in hours and minutes. Flight Information Region Gives the abbreviation for the FIR (YMMM or YBBB) in which the phenomenon is located. Identifier The message identifier is SIGMET. Daily Sequence Number The four-character sequence number consists of: a two-letter designator to indicate the general location of the event (as given in the two maps below), and a two-digit number, giving the sequence number of SIGMETs issued by the relevant office within the FIR (Brisbane or Melbourne) since 0000 UTC. The tropical cyclone and low-level SIGMET two-letter designators and their associated geographical extent are: The high-level (above FL185) icing and turbulence SIGMET two-letter designators and their general associated geographical extent are: Validity Period The validity period is given in the format DDHHMM/DDHHMM, where DD is the day of the month and HHMM is the time in hours and minutes UTC. Tropical cyclone and volcanic ash SIGMETs can have a validity of up to six hours. SIGMETs for other phenomena can be valid for up to four hours. Originating Office (ICAO Indicator) The International Civil Aviation Organization (ICAO) location indicators for Australian Meteorological Watch Offices are: YPRM - Adelaide Regional Forecasting Centre YPRF - Perth Regional Forecasting Centre YBRF - Brisbane Regional Forecasting Centre YSRF - Sydney Regional Forecasting Centre YPDM - Darwin Regional Forecasting Centre YMRF - Melbourne Regional Forecasting Centre YMHF - Hobart Regional Forecasting Centre YBTL - Townsville Meteorological Office YMMC - Melbourne Aviation Weather Centre Flight Information Region This gives the abbreviation and full name for the FIR in which the phenomenon is located. Meteorological Information This section includes: type of phenomenon observed or forecast location, both horizontal and vertical extents movement or expected movement expected change in intensity SIGMET for tropical cyclone and volcanic ash cloud include a forecast position for the end of the validity period message status Cancel SIGMET If during the validity period of a SIGMET, the phenomenon for which the SIGMET is no longer occurring or is no longer expected, the SIGMET is cancelled by issuing a SIGMET with the abbreviation CNL in lieu of meteorological information. SIGMET Status The status line indicates whether the SIGMET is: NEW - the SIGMET is for a new phenomenon. REV - the SIGMET reviews an earlier SIGMET for the phenomenon. CNL - cancels a current SIGMET. The following abbreviations are used in SIGMET: Code and Description A - Altitude ABV - Above APRX - Approximately BLW - Below CNL - Cancel DS - Dust storm EMBD - Embedded FIR - Flight Information Region FCST - Forecast FL - Flight level FRQ - Frequent FZRA - Freezing rain GR - Hail HVY - Heavy ICE - Icing INTSF - Intensifying LOC - Location MOV - Moving NC - No Change (intensity) OBS - Observed OBSC - Obscured RDOACT CLD - Radioactive cloud REV - Review SEV - Severe SQL - Squall line SS - Sand storm STNR - Stationary STS - Status TC - Tropical cyclone TS - Thunderstorm TURB - Turbulence VA - Volcanic ash WI - Within (area) WKN - Weakening (intensity) Z - Universal Time SIGMET Examples WSAU21 AMMC 180357 YMMM SIGMET MM01 VALID 180439/180839 YMMC- YMMM MELBOURNE FIR SEV TURB FCST WI S3200 E12800 - S3200 E13000 - S4700 E13600 - S4700 E13400 FL260/400 MOV E 25KT NC STS:NEW WSAU21 AMMC 180720 YMMM SIGMET MM02 VALID 180720/180839 YMMC- YMMM MELBOURNE FIR CNL SIGMET MM01 180439/180839 STS:CNL SIGMET MM01 180439/180839 WCAU01 APRF 180217 YMMM SIGMET PH01 VALID 180215/180815 YPRF- YMMM MELBOURNE FIR TC ILSA OBS AT 0000Z S1330 E11324 CB TOP FL500 WI 120NM OF CENTRE MOV WSW 17KT INTSF FCST 0815Z TC CENTRE S1418 E11036 STS:NEW WVAU01 ADRM 200100 YBBB SIGMET BT04 VALID 200100/200700 YPDM- YBBB BRISBANE FIR VA ERUPTION LOC S0416 E15212 VA CLD OBS AT 200100Z A100/180 APRX 120NM BY 40NM S1130 E14530 - S1330 E14900 - S1030 E15030 - S0830 E14700 - S1130 E14430 MOV SW 20KT FCST 0700Z VA CLD APRX S110 E144530 - S1230 E14930 - S1050 E15130 - S0800 E14700 - S1130 E14400 STS:REV SIGMET BT03 191900/200100
