Aviation Weather Guide · 6 min read
A TAF (Terminal Aerodrome Forecast) is a weather forecast for the airspace within 5 statute miles of an airport, issued every 6 hours and valid for 24–30 hours. It uses the same format as a METAR but adds change groups to describe how conditions will evolve.
TAFTAF is a standard forecast. TAF AMD is an amended forecast issued when conditions change significantly before the next scheduled issuance.
KLAX 151720ZSame as METAR: 4-letter ICAO identifier and the UTC date/time the forecast was issued (day 15, 17:20Z).
1518/1624The forecast is valid from day 15 at 18:00Z through day 16 at 24:00Z (midnight). Format is DDHH/DDHH.
The first line after the header describes expected conditions at the start of the valid period — same fields as a METAR (wind, visibility, sky conditions).
FM160200A permanent change. From day 16 at 02:00Z, all previous conditions are replaced by the new line. Use FM when a front or significant shift is expected.
TEMPO 1518/1522Conditions that last less than half the time during the period and each occurrence lasts less than 60 minutes. The base conditions still apply outside the TEMPO window. Here: between 18:00Z and 22:00Z on day 15, expect gusts to 25 kt and 4SM visibility in mist with a broken ceiling at 1,500 ft.
BECMG 1608/1610A gradual, permanent change expected to occur between the two times. By 10:00Z on day 16, winds will have become variable at 3 kt. Unlike FM, the change happens gradually over the window.
PROB30 or PROB40 indicates a 30% or 40% probability of the following conditions. You won't see PROB50 or higher — forecasters use TEMPO instead. PROB30 is a heads-up; PROB40 warrants more attention.