An AIRMET is an advisory that includes hazardous weather phenomena for light aircraft.
An AIRMET is issued every six hours with updates issued as needed. The information in an AIRMET is of operational interest for all aircraft, but the weather section includes potentially hazardous phenomena for light aircraft. Three types of AIRMETs are listed below.
AIRMET Sierra describes IFR (instrument flight rules) conditions and/or extensive mountain obscurations.
AIRMET Tango describes moderate turbulence, sustained surface winds of 30 knots or greater, and Non-Convective low-level wind shear.
AIRMET Zulu describes moderate icing and provides freezing-level heights.
FAA AC 00-45H Aviation Weather Services pg. 5-16, 5-21
FAA-H-8083-25B Pilot’s Handbook of Aeronautical Knowledge pg. 13-8