Warning Messages — Page 512, Lesson 494

I want to walk you through SIGMETs and volcanic ash advisories — two critical warning messages you'll rely on as a professional pilot. Let's start with SIGMET. A SIGMET is a warning about significant weather hazards that could affect aircraft within a flight information region, or FIR. Importantly, SIGMETs are not issued for hazards at aerodromes — they cover en-route conditions. The competent meteorological watch office issues a SIGMET when hazardous conditions are either forecast or have been reported by aircraft. ICAO requires that SIGMETs are valid for 4 hours. However, there are two exceptions: SIGMETs for tropical cyclones — identified by the code WC — and SIGMETs for volcanic ash — identified by the code WV — are valid for 6 hours. In practice, the validity period is whatever is stated in the message itself. Now, what hazards trigger a SIGMET? The list includes: thunderstorm, heavy hail, tropical cyclone, freezing rain, severe turbulence not associated with convective cloud, severe icing not associated with convective cloud, severe mountain waves, heavy sand or dust storm, and volcanic ash cloud. The SIGMET message uses an abbreviated text format that's relatively easy to interpret once you know the codes. Let me run through the common abbreviations you'll see. BTN means between. CNL means cancelled. EMBD means embedded — that's when cumulonimbus or thunderstorm clouds are contained within stratiform cloud. FRQ means frequent, indicating little or no separation between adjacent thunderstorms. INTSF means intensifying. ISOL means isolated — individual CB or thunderstorm cells. MTW stands for mountain waves. NC means no change. OBS means obscured — CB or thunderstorms hidden by haze, smoke, or darkness. OCNL means occasional — well-separated CB or thunderstorms. OTLK means outlook. SQL means squall line — a line of thunderstorms with little or no separation between individual clouds. STNR means stationary. TC is tropical cyclone. VA is volcanic ash. WKN means weakening. Let me walk you through a real SIGMET example so you can see how this all comes together. The message reads: EGPX SIGMET 02 VALID 091115/091715 EGRR- Breaking that down: EGPX is the Scottish flight information region. This is the second SIGMET issued for that FIR — that's the 02. It's valid from 1115 Zulu to 1715 Zulu on the 9th of the month. EGRR is the meteorological watch office at Exeter that issued it. Then the body: SEV TURB FCST AND OBS BLW FL060 NW OF A LINE N5425 W00810 TO N5900 E00200 MOV SE AT 20KT AND SE OF LINE N5800 W01000 TO N6100 W00800 MOV SE AT 25KT NC. So severe turbulence is both forecast and observed below flight level 060. Northwest of a line from 5425 North, 00810 West to 5900 North, 00200 East, that turbulence is moving southeast at 20 knots. And southeast of a line from 5800 North, 01000 West to 6100 North, 00800 West, it's moving southeast at 25 knots. NC at the end means no change in intensity expected. Now let's move to volcanic ash. ICAO, in conjunction with the World Meteorological Organization, has established 9 volcanic ash advisory centres, or VAACs. These centres are operated by the national meteorological services of their respective countries. Their responsibility is detecting volcanic ash clouds, tracking them, and forecasting their future movement both horizontally and vertically. Here's an example of a VAAC advisory message. Note that these messages may be reissued as a SIGMET with the code WV by the meteorological watch office. The message starts with FVFE01 RJTD 010045 — that's the message identifier. Then VA ADVISORY tells you the type of message. DTG is the date-time group: 2012/08/01 at 0045 Zulu. VAAC: TOKYO is the issuing centre. VOLCANO: SAKURAJIMA 0802-08 gives you the volcano name and its international identity number. PSN: N3135E13040 is the position — 31 degrees 35 minutes North, 130 degrees 40 minutes East. AREA: JAPAN. SUMMIT ELEV: 1060 metres. ADVISORY NR: 2012/656 is the sequence number. INFO SOURCE: JMA — that's the Japan Meteorological Agency. And AVIATION COLOUR CODE: NIL — we'll cover what that colour code means in a moment. That's the core of how SIGMETs and volcanic ash advisories work. You'll need to be able to read these messages quickly and accurately in flight planning and in the air.