SIGMET

SIGMETs exist to flag weather dangerous enough to affect the safety of aircraft in flight, distinct from routine forecasts. They are issued for a defined list of phenomena — among them thunderstorms, severe or extreme turbulence, severe icing, severe mountain waves, dust and sandstorms, volcanic ash and tropical cyclones — by the meteorological watch office responsible for a flight information region, and they specify the area affected, the altitudes, the movement and the period of validity.

Because they concern hazardous en-route conditions, SIGMETs feed directly into flight planning and in-flight decisions about routing, altitude and timing. Volcanic ash SIGMETs in particular can have far-reaching operational effects, since ash can damage engines and force large-scale rerouting or airspace avoidance. SIGMETs complement other meteorological products and pilot reports to build a current picture of the en-route environment.

SIGMETs sit on the safety side of operational risk rather than the security side. AeroVigil's focus is the consolidation of security and airspace-risk signals; advisories such as SIGMETs illustrate the kind of authoritative, time-bound hazard information that, alongside security intelligence, shapes how a route is flown.