Weather

TAF Explained: How to Decode an Aviation Forecast

15 July 2026 · 2 min read

Where a METAR tells you the weather now, a TAF (Terminal Aerodrome Forecast) tells you what to expect over the next 24 to 30 hours around an airport. It uses almost the same codes as a METAR, plus a handful of “change groups” that describe how conditions will evolve. Master those and you can plan a flight with confidence.

Try it yourself: Decode any airport in seconds with our free Live METAR & TAF Decoder — it turns the raw code into plain English instantly.

The structure of a TAF

A TAF starts with the station and issue time, then a validity period, then a base forecast, followed by any changes. Here is an example:

TAF EGLL 150854Z 1509/1615 05010KT 9999 SCT025 BECMG 1512/1515 20015KT PROB40 TEMPO 1518/1522 7000 -RA BKN012

Validity period

1509/1615 means the forecast is valid from the 15th at 09:00Z until the 16th at 15:00Z. The two pairs are day-and-hour in UTC.

Base forecast

The groups straight after the validity are the prevailing conditions expected at the start: wind 05010KT (from 050° at 10 kt), visibility 9999 (10 km+) and SCT025 (scattered cloud at 2,500 ft). These read exactly like a METAR.

Change groups — the heart of a TAF

FM (From): a rapid, permanent change at a specific time. FM151600 means “from 16:00Z on the 15th, conditions become…” and everything after replaces the previous picture.
BECMG (Becoming): a gradual change over a stated window. BECMG 1512/1515 means the change happens progressively between 12:00Z and 15:00Z.
TEMPO (Temporarily): short-lived fluctuations, each lasting under an hour and totalling less than half the period. Good for showers or gusts that come and go.
PROB30 / PROB40: a 30% or 40% probability of the conditions that follow. Often paired with TEMPO, as in PROB40 TEMPO.

So in our example, the wind is forecast to become 200° at 15 kt between 12:00 and 15:00Z, with a 40% chance of temporary rain reducing visibility to 7,000 m with cloud broken at 1,200 ft between 18:00 and 22:00Z.

Why TAFs matter for planning

A TAF lets you answer the key questions before you commit: will I need an alternate? Is there a risk of the destination going below minimums while I am en route? Reading the change groups tells you not just what the weather will be, but when and how likely.

Frequently asked questions

How long is a TAF valid?

Most TAFs cover 24 hours; major airports issue 30-hour TAFs, updated every six hours.

What does TAF AMD mean?

AMD is an amended TAF, reissued when the forecast changes materially. COR is a correction to a previous one.

Is a TAF a guarantee?

No — it is a forecast. Always cross-check the latest METAR and, for real flights, an approved briefing source. New to the codes? Start with our guide to reading a METAR.

Explore more in the Aviation Weather hub.