ADDS - Aviation Digital Data Service

ADDS - AIRMETs Help Page (2 of 4)
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An AIRMET (AIRman's METeorological Information) advises of weather potentially hazardous to all aircraft but that does not meet SIGMET criteria.
   AIRMETs are issued by the National Weather Service's Aviation Weather Center (for the lower 48 states and adjacent coastal waters) for the following weather-impacted reasons:
  • Instrument Flight Rules (IFR) or Mountain Obscuration -
    • Ceilings less than 1000 feet and/or visibility less than 3 miles affecting over 50% of the area at one time.
    • Extensive mountain obscuration
  • Turbulence
    • Moderate Turbulence
    • Sustained surface winds of greater than 30 knots at the surface
  • Icing
    • Moderate icing
    • Freezing levels
   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.
   AIRMETs are routinely issued for 6 hour periods beginning at 0245 UTC. AIRMETS are also amended as necessary due to changing weather conditions or issuance/cancellation of a SIGMET.