TAF (Terminal Aerodrome Forecast) is the ICAO coded forecast for an aerodrome, issued every 6 hours with 24–30-hour validity. It uses the same format as METAR with additional groups (BECMG, TEMPO, PROB) indicating expected changes.
Change groups
BECMG (becoming): gradual permanent change. TEMPO: temporary fluctuation lasting less than 1 hour. PROB30/PROB40: 30–40% probability. TAFs are mandatory for flight planning; a pilot cannot legally depart for a destination whose TAF indicates conditions below landing minima.