SIGMET

What is SIGMET?

A SIGMET (Significant Meteorological Information) is a weather advisory issued by Meteorological Watch Offices alerting pilots to en-route hazards including thunderstorms, severe turbulence, severe icing, mountain waves, and volcanic ash. SIGMETs cover large geographic regions with validity periods typically of four to six hours.

TS

Thunderstorms

TURB

Severe turbulence

ICE

Severe icing

MTW

Mountain wave

VA

Volcanic ash

How is SIGMET used?

SIGMETs are distributed through Aeronautical Information Services, ATIS broadcasts at major airports, and pre-flight briefing systems. A typical SIGMET such as 'SIGMET 1 VALID 1200/1800 EDUB TS FCST EMBD TS MOV NE SEV TURB SFC/FL300' tells the pilot there are embedded thunderstorms forecast to move northeast with severe turbulence from surface to flight level 300 between 12:00 and 18:00 UTC. Pilots reroute around SIGMET-affected areas where possible, or delay departure to avoid the advisory window. Commercial operators review SIGMETs in pre-departure briefings and file amended routes to avoid areas of severe weather. Volcanic ash SIGMETs are treated with particular seriousness because jet engines can flame out in ash clouds, as demonstrated during the 2010 Eyjafjallajokull eruption that closed European airspace for days. EASA theoretical knowledge exams test SIGMET format and interpretation in both Meteorology and Operational Procedures subjects.