Definition
AIRMETS are in-flight weather advisories issued by the National Weather Service to alert pilots of weather phenomena that may affect aircraft safety but are less severe than those described in SIGMETs. They cover conditions such as moderate icing, moderate turbulence, sustained surface winds of 30 knots or greater, widespread areas of ceilings less than 1,000 feet and/or visibility less than 3 miles, and extensive mountain obscurement. AIRMETS are of particular concern to pilots of light aircraft and those without adequate instrumentation or training for instrument flight.
Plain English
Weather warnings sent out to pilots while they're flying, telling them about weather that could cause trouble but isn't as dangerous as the worst stuff. Things like bumpy air, ice forming on the aircraft, strong surface winds, low clouds, poor visibility, or mountains hidden by clouds.
Context Anchor
Pilots encounter AIRMETS during preflight weather planning and in inflight weather advisory broadcasts such as Hazardous Inflight Weather Advisory Service broadcasts.
Derivation
From AIRman's METeorological information. The name signals that the advisory is aimed directly at pilots (airmen) and concerns weather (meteorology) that affects flight.
Why Pilots Care
Allows pilots to anticipate conditions that may require route changes, altitude adjustments, or delays to maintain safety.
Grounding Statement
An AIRMET means a weather problem is spread out enough, and important enough, that pilots in that area should plan around it.
Intuition Check
Do not treat an AIRMET as just a casual weather note. It is an official advisory about conditions that can matter to safety, even if they are not the most severe weather warnings.
Example Sentence 1
During the preflight briefing, the pilot noted an AIRMET for moderate icing between 6,000 and 12,000 feet along the planned route and chose to fly lower to stay clear of the freezing layer.
Example Sentence 2
AIRMETS indicated mountain obscuration, so the flight stayed over lower terrain.