(1) Canada: Short-term meteorological information intended primarily for aircraft in flight, to notify pilots of potentially hazardous weather conditions not described in the current area forecast and not requiring a SIGMET. The criteria for issuing an AIRMET are the unforeseen development, dissipation or non-occurrence of forecast

(a) instrument meteorological conditions (IMC): broken or overcast cloud condition at less than 1000 ft AGL and/or visibility less than 3 SM;

(b) freezing precipitation (not requiring a SIGMET);

(c) moderate icing;

(d) moderate turbulence;

(e) thunderstorms (isolated as opposed to a line);

(f) an increase in the surface mean wind over a large area to 20 kt or more, or an increase in gusts to 30 kt or more, when no winds were originally forecast; or

(g) a difference between the forecast and observed wind direction greater than 60°.

(2) U.S.: In-flight weather advisories issued only to amend the area forecast concerning weather phenomena which are of operational interest to all aircraft and potentially hazardous to aircraft having limited capability because of lack of equipment, instrumentation, or pilot qualifications. AIRMETs concern weather of less severity than that covered by SIGMETs or convective SIGMETs. AIRMETs cover moderate icing, moderate turbulence, sustained winds of 30 kt or more at the surface, widespread areas of ceilings less than 1000 ft and/or visibility less than 3 mi., and extensive mountain obscurement.