Definition
An in-flight weather advisory issued by the National Weather Service to warn pilots of weather phenomena considered hazardous to all aircraft, regardless of size or type. Sigmets cover severe icing not associated with thunderstorms, severe or extreme turbulence or clear air turbulence not associated with thunderstorms, dust storms or sandstorms lowering surface visibility to below three miles, and volcanic ash. Convective Sigmets, issued separately, cover thunderstorm-related hazards.
Plain English
A weather warning sent to pilots in flight about conditions dangerous enough to threaten any aircraft, like severe icing, severe turbulence, dust storms, or volcanic ash.
Context Anchor
Pilots see Sigmets during preflight weather planning, in weather briefings, and in cockpit weather displays while deciding whether a route is safe to fly.
Derivation
Formed from SIG (significant) + MET (meteorological). The construction signals that this is weather information important enough to warrant a specific warning, not a routine update.
Why Pilots Care
Pilots must know about these conditions so they can reroute, delay, or cancel a flight to avoid loss of aircraft control or structural damage.
Grounding Statement
If a Sigmet covers your planned route, picture a marked area of dangerous weather that you should not simply fly into without a clear plan.
Intuition Check
A Sigmet is not a forecast of bad weather in general. It is a specific warning that conditions are severe enough to threaten every aircraft in the affected area.
Example Sentence 1
Center advised us of a Sigmet for severe turbulence over the Rockies, so we requested a lower altitude to avoid the worst of it.
Example Sentence 2
During the weather briefing we reviewed the current SIGMETs before filing the flight plan.