AIRMETS — IFR and Mountain Obscuration AIRMETS are depicted as solid yellow lines. The type of AIRMET is labeled as either IFR or MTOS (Mountain Obscuration). The start and expiration time of the AIRMET is depicted below the AIRMET label, with the two digit day of month followed by the 4 digit hour and minute in UTC. IFR & Mountain Obscuration AIRMETS (named SIERRA) are issued for areas where IFR or mountain obscuration conditions are expected over 50% of the defined area.
Maps are updated every hour and are available between 30 and 45 minutes past each hour to depict the most current AIRMETs. AIRMETs are issued by the AWC at 0145, 0745, 1345 and 1945 UTC.