Definition
An in-flight weather advisory issued by the National Weather Service to alert pilots of weather phenomena that are potentially hazardous to all aircraft, regardless of size or type. SIGMETs cover conditions such as severe or extreme turbulence, severe icing, and widespread dust storms, sandstorms, or volcanic ash that reduce visibility to less than three miles. A separate category, Convective SIGMET, addresses thunderstorm-related hazards.
Plain English
A weather warning sent to pilots in flight when conditions are dangerous enough to threaten any aircraft, not just small ones. It covers things like very rough air, heavy ice buildup, ash from volcanoes, or massive dust storms.
Context Anchor
Seen in aviation weather briefings, flight planning tools, and in-flight weather updates.
Derivation
Built from 'significant' (meaning notable or important enough to matter), 'meteorological' (from Greek meteoros, 'high in the air,' the study of atmospheric conditions), and 'information.' The combined term signals weather information important enough that every pilot needs to know about it.
Why Pilots Care
These advisories directly affect route planning, altitude choices, and go/no-go decisions to prevent encounters that could cause loss of aircraft control.
Intuition Check
Significant does not mean merely interesting or noticeable here. It means serious enough to matter to the safety of all aircraft in the affected area.
Example Sentence 1
Center advised us of a SIGMET for severe turbulence over the ridge line, so we requested a lower altitude before entering the area.
Example Sentence 2
A Significant Meteorological Information report for severe icing forced the crew to descend and divert to an alternate airport.