In meteorology and aviation, terminal aerodrome forecast (TAF) is a format for reporting weather forecast information, particularly as it relates to aviation. TAFs are issued at least four times a day, every six hours, for major civil airfields: 0000, 0600, 1200 and 1800 UTC, and generally apply to a 24- or 30-hour period, and an area within approximately five statute miles (8.0 km) (or 5 nautical miles (9.3 km) in Canada) from the center of an airport runway complex. TAFs are issued every three hours for military airfields and some civil airfields and cover a period ranging from 3 hours to 30 hours.
TAFs complement and use similar encoding to METAR reports. They are produced by a human forecaster based on the ground. For this reason there are considerably fewer TAF locations than there are airports for which METARs are available. TAFs can be more accurate than Numerical Weather Forecasts, since they take into account local, small-scale, geographic effects.
In the United States the weather forecasters responsible for the TAFs in their respective areas are located within one of the 122 Weather Forecast Offices operated by the United States' National Weather Service. In contrast, a trend type forecast (TTF), which is similar to a TAF, is always produced by a person on-site where the TTF applies. In the United Kingdom most TAFs at military airfields are produced locally, however TAFs for civil airfields are produced at the Met Office headquarters in Exeter.
The United States Air Force employs active duty enlisted personnel as TAF writers. Air Force weather personnel are responsible for providing weather support for all Air Force and Army operations.
Different countries use different change criteria for their weather groups. In the United Kingdom, TAFs for military airfields use colour states as one of the change criteria. Civil airfields in the UK use slightly different criteria.
This TAF example of a 30-hour TAF, released on November 5, 2008 at 1730 UTC:
TAF KXYZ 051730Z 0518/0624 31008KT 3SM -SHRA BKN020 FM052300 30006KT 5SM -SHRA OVC030 PROB30 0604/0606 VRB20G35KT 1SM TSRA BKN015CB FM060600 25010KT 4SM -SHRA OVC050 TEMPO 0608/0611 2SM -SHRA OVC030 RMK NXT FCST BY 00Z=
The first line contains identification and validity times.
The remainder of the first line contain the initial forecast conditions. Variations of the codes used for various weather conditions are many.
Each line beginning with FM indicates a rapid change in the weather over a period of less than an hour.
The final line is for errata, comments, and remarks.