Definition
A SIGMET is an in-flight weather advisory issued by the National Weather Service to warn pilots of weather phenomena that are potentially hazardous to all aircraft, regardless of size or type. SIGMETs cover severe icing not associated with thunderstorms, severe or extreme turbulence not associated with thunderstorms, dust storms or sandstorms lowering visibility to less than three miles, and volcanic ash. A separate category, Convective SIGMET, covers thunderstorm-related hazards.
Plain English
A SIGMET is a weather warning sent out during flight to alert all pilots about serious weather that could be dangerous to any aircraft, such as severe turbulence, severe icing, dust storms, or volcanic ash.
Context Anchor
Pilots encounter SIGMETs during weather briefings, flight planning, and in-flight weather updates, especially before or during instrument flights.
Derivation
Built from SIG (significant) + MET (meteorological). The name signals the threshold: only weather significant enough to threaten any aircraft earns a SIGMET. Lesser hazards are issued as AIRMETs (Airmen's Meteorological Information) instead.
Why Pilots Care
Pilots review SIGMETs to avoid weather that could cause loss of aircraft control or structural damage.
Grounding Statement
If a SIGMET covers your planned route, treat it as a serious weather warning, not just a routine weather note.
Intuition Check
“Significant” does not just mean noticeable or interesting here. In a SIGMET, it means important enough to be a possible safety hazard for aircraft.
Example Sentence 1
During the preflight briefing, the dispatcher pointed out a SIGMET for severe turbulence between FL280 and FL360 along the planned route.
Example Sentence 2
A convective SIGMET warned of embedded thunderstorms along the planned route.