TAF Decoder

How to read a TAF

A TAF is a coded aviation weather forecast for an aerodrome. It describes expected conditions during a defined forecast period, including wind, visibility, significant weather and cloud cover.

Reading a TAF from left to right starts with the report identity, aerodrome, issue time and validity period. The prevailing forecast follows, with additional groups describing expected changes or temporary conditions later in the period.

TAF format and forecast groups

A TAF normally contains an aerodrome identifier, issue time, validity period and prevailing forecast conditions. Depending on the forecast, it can also contain FM, TEMPO, BECMG or probability groups, as well as forecast maximum and minimum temperatures where applicable.

Aerodrome and issue time

The aerodrome identifier shows which location the forecast applies to. The issue-time group uses UTC. For example,151100Z means the forecast was issued on the 15th day of the month at 11:00 UTC.

TAF validity period

The validity group defines when the forecast applies. A group such as 1512/1618 means the forecast is valid from 12:00 UTC on the 15th until 18:00 UTC on the 16th.

Wind

TAF wind groups use the same compact direction-and-speed style familiar from aerodrome weather reports. For example,24010KT forecasts wind from 240 degrees at 10 knots. Gusts and variable wind can also appear in TAF wind groups.

Visibility, weather and CAVOK

Forecast visibility can be followed by significant weather such as rain, snow, fog, showers or thunderstorms.9999 represents visibility of 10 kilometres or more. CAVOK may be used when the applicable visibility, weather and cloud criteria are forecast to be met.

Individual abbreviations such as SHRA,TSRA and cloud amount codes can be checked in the Aviation Weather Codes reference.

Cloud groups

Forecast cloud groups combine cloud amount and height. For example, BKN010 means broken cloud at 1,000 feet. TAFs can also contain significant convective cloud types and applicable clear-sky or no-significant-cloud forms.

TAF change groups

A major part of reading a TAF is understanding when forecast conditions change. Change groups divide the forecast into periods or describe conditions expected only during part of the validity window.

FM — from

An FM group introduces a new set of prevailing forecast conditions beginning at the stated time. Conditions following the FM group replace the previous prevailing conditions for the subsequent period until another applicable change occurs.

TEMPO — temporary conditions

TEMPO describes temporary fluctuations expected during a stated interval. The conditions in the TEMPO group do not replace the prevailing forecast for the entire interval.

BECMG — becoming

BECMG indicates a transition to forecast conditions during a specified period. AviationDecoder keeps the interval separate from the surrounding forecast so the change can be read in context.

TAF probability groups: PROB30 and PROB40

Probability groups express a 30 or 40 percent probability of specified forecast conditions. They appear asPROB30 or PROB40 and can also be associated with temporary-condition groups.

The decoder presents probability and validity information separately so a possible condition is not confused with the prevailing forecast.

TAF example decoded

TAF EGLL 151100Z 1512/1618 24010KT 9999 SCT025 TEMPO 1518/1522 3000 SHRA BKN010

This example is a forecast for EGLL issued at 11:00 UTC on the 15th and valid from 12:00 UTC on the 15th until 18:00 UTC on the 16th. The prevailing forecast has wind from 240 degrees at 10 knots, visibility of at least 10 km and scattered cloud at 2,500 feet.

Between 18:00 and 22:00 UTC on the 15th, temporary conditions forecast visibility of 3,000 metres, rain showers and broken cloud at 1,000 feet.

Forecast temperatures

Some TAF formats include forecast maximum and minimum temperatures. TX and TN groups give the temperature and associated forecast time, including negative-temperature notation.

TAF decoder coverage

Decoded TAF groups include wind and gusts, visibility, significant weather, cloud layers, CAVOK, NSW, clear-sky conditions, FM periods, TEMPO and BECMG intervals, PROB30 and PROB40 groups, PROB/TEMPO combinations and forecast maximum and minimum temperatures.

Unsupported forecast content is preserved rather than silently assigned an invented interpretation, keeping the decoded result traceable to the original TAF.

Related aviation weather tools

Decode current aerodrome observations with the METAR Decoder. Individual forecast weather and cloud abbreviations can be checked in the Aviation Weather Codes reference. For pilot-reported conditions, use the PIREP Decoder.