AIRMET (AIRman's METeorological Information) advises of weather that
maybe hazardous, other than convective activity, to single engine, other
light aircraft, and Visual Flight Rule (VFR) pilots. However, operators
of large aircraft may also be concerned with these phenomena. The items
AIRMET Sierra (IFR):
- Ceilings less than 1000 feet and/or visibility less than 3 miles
affecting over 50% of the area at one time.
- Extensive mountain obscuration
AIRMET Tango (Turbulence):
- Moderate turbulence
- Sustained surface winds of 30 knots or more at the surface
AIRMET Zulu (Icing):
These AIRMET items are considered to be widespread because they must be
affecting or be forecast to affect an area of at least 3000 square miles
at any one time. However, if the total area to be affected during the
forecast period is very large, it could be that only a small portion of
this total area would be affected at any one time.
- Moderate icing
- Freezing levels
AIRMETs are routinely
issued for 6 hour periods beginning at 0145 UTC during Central Daylight
Time and at 0245 UTC during Central Standard Time. AIRMETS are also amended
as necessary due to changing weather conditions or issuance/cancelation
of a SIGMET .