Aero Academic
Aero Academic
In-flight weather advisories: AIRMETs cover hazards significant to light aircraft, SIGMETs cover hazards significant to all aircraft.
AIRMETs (Airmen's Meteorological Information) and SIGMETs (Significant Meteorological Information) are both in-flight weather advisories issued to warn pilots of hazardous conditions en route, but they differ in severity and who they are written for. An AIRMET covers weather that is significant to smaller aircraft or less experienced pilots but may not be hazardous to larger, faster aircraft.
There are three AIRMET series. AIRMET Sierra covers IFR conditions (ceilings below 1,000 ft and/or visibility below 3 statute miles) and mountain obscuration. AIRMET Tango covers moderate turbulence, sustained surface winds of 30 knots or greater, and low-level wind shear. AIRMET Zulu covers moderate icing and freezing levels.
A SIGMET, by contrast, warns of weather hazardous to all aircraft regardless of size — severe turbulence, severe icing, dust storms, volcanic ash, and widespread duststorms or sandstorms reducing visibility below 3 statute miles. A Convective SIGMET specifically covers thunderstorm-related hazards: embedded or severe thunderstorms, lines of thunderstorms, or hail 3/4 inch or greater.