USAviation.info explains the subject in plain language. For flight, maintenance, certification or regulatory decisions, use the current official source and applicable approvals, procedures and guidance.
METAR — airport observation
A METAR is a coded surface weather observation for an airport or reporting station. It can include wind, visibility, weather phenomena, cloud information, temperature/dew point and altimeter setting. It describes observed conditions rather than a forecast.
TAF — terminal forecast
A TAF is a coded forecast for conditions expected in the vicinity of a terminal during its valid period. It commonly addresses wind, visibility, significant weather and cloud/ceiling conditions.
PIREP / AIREP — reports from aircraft
Pilot Reports (PIREPs) and aircraft reports provide observations from aircraft in flight. They can supply operationally important information on turbulence, icing, cloud tops/bases, visibility, winds and other conditions that may not be captured by surface observations alone.
SIGMET and G-AIRMET — hazard information
SIGMETs provide warnings for significant aviation weather hazards. G-AIRMETs provide graphical advisory information for the contiguous United States. The Aviation Weather Center states that CONUS text AIRMETs were discontinued in January 2025 and replaced by G-AIRMETs; Alaska continues to use AIRMET products.
Use a complete briefing source
These products are components of weather awareness, not substitutes for a complete preflight briefing. For operational decisions, use current official products and an appropriate briefing source such as Flight Service.