Plain English Meaning

A SIGMET is an official weather warning sent out to pilots in flight about serious weather that could be dangerous for any aircraft, such as severe turbulence, severe icing, dust storms, or volcanic ash.

Full Definition

A SIGMET is an in-flight weather advisory issued by the National Weather Service warning of weather hazards considered significant to all aircraft, regardless of size or type. SIGMETs cover non-convective hazards including severe or extreme turbulence not associated with thunderstorms, severe icing not associated with thunderstorms, and widespread dust storms, , or volcanic ash that lower or in-flight visibilities to below three miles. In the contiguous , SIGMETs are issued for four-hour periods (six hours for volcanic ash) and identified by an alphabetic designator from November through Yankee, excluding and .