Terminal Aerodrome Forecast

In meteorology and aviation, TAF is a format for reporting weather forecast information, particularly as it relates to aviation. "TAF" is an acronym of Terminal Aerodrome Forecast or, in some countries, Terminal Area Forecast. Generally a TAF is a 9- or 12-hour forecast, though some TAFs can cover an 18- or 24-hour period. They are updated every 6 hours at 00:00Z, 06:00Z, 12:00Z, and 18:00Z.

Recently the ICAO announced that beginning November 5, 2008 TAFs for some major airports will cover 30 hours. Therefore the time group will have to carry a new format worldwide to include the day.

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 fewer TAF locations than there are METARs. 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 forecaster responsible for a TAF is not usually stationed at the location that the TAF applies to. The forecaster usually work from a centralised location responsible for many TAFs in a state or region, many of which are over 100 miles away from the forecaster's location. In contrast, a TTF (Trend Type Forecast), 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 TAF writers as enlisted personnel. 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.

TAF Code

This TAF example is from Calgary International Airport, Calgary, Alberta, and was released on October 19 2006 at 2038 UTC:

TAF CYYC 192038Z 192118 17008KT P6SM SCT020 OVC080 TEMPO 2203 P6SM -SHRABECMG 2223 24007KTFM0300Z 32010KT P6SM SCT007 BKN060FM0600Z 33015KT P6SM SCT010 BKN040 TEMPO 0612 5SM -RASN BR OVC010FM1200Z 34015G25KT P6SM SCT010 OVC030 TEMPO 1218 2SM -SHSN OVC010RMK NXT FCST BY 00Z=

*TAF indicates that the following is a terminal area forecast.
*CYYC indicates that the report came from Calgary International Airport.
*192038Z indicates that the report was issued at 2038 UTC on the 19th of the month.
*192118 indicates that the report is valid from 2100 UTC on the 19th until 1800 UTC on the following day.
*17008KT indicates that the forecast wind at 2100 UTC will initially be from 170 degrees at 8 knots.
*P6SM indicates that visibility is forecast to be at least six statute miles. Forecast visibility of six miles or more is always referred to as P6SM. The P stands for Plus.
*SCT020 OVC080 indicates that clouds are forecast to be scattered at 2000 feet and overcast at 8000 feet, all heights AGL.
*TEMPO 2203 P6SM -SHRA indicates that between 2200 and 0300 there may be at times light rain showers with visibility of at least six statute miles.
*BECMG 2223 24007KT indicates that a wind shift to 240 degrees at 7 knots is forecast to occur between 2200 and 2300 UTC.
*FM0300Z 32010KT P6SM SCT007 BKN060 indicates that beginning at 0300 UTC the wind will be from 320 degrees at 10 knots, visibility will be at least six statute miles, and clouds will be scattered at 700 feet and broken at 6000 feet.
*FM0600Z 33015KT P6SM SCT010 BKN040 TEMPO 0612 5SM -RASN BR OVC010 indicates that beginning at 0600 UTC the wind will be from 330 degrees at 15 knots, visibility will be at least six statute miles, and clouds will be scattered at 1000 feet and broken at 4000 feet. There is forecast to be at times between 0600 and 1200 hours visibility at 5 statute miles, light rain and snow, and mist with an overcast layer of cloud at 1000 feet.
*FM1200Z 34015G25KT P6SM SCT010 OVC030 TEMPO 1218 2SM -SHSN OVC010 indicates that beginning at 1200 UTC the wind will be from 340 degrees at 15 knots gusting to 25 knots, visibility will be at least six statute miles, and clouds will be scattered at 1000 feet and overcast at 3000 feet. There is also forecast to be at times between 1200 and 1800 hours visibility of two statute miles, light snow showers, and an overcast layer of cloud at 1000 feet.
*RMK NXT FCST BY 00Z indicates that the next forecast will be issued by 0000 UTC.

TAF Rules

TAF's must follow a set of rules that define what must be placed in each line and what criteria requires a new line. There are four different lines in a TAF. The first one gives location, valid time and given weather for that time until the next line of the forecast. A BECMG (becoming) line indicates that in the period given, the weather will start to change from the previous line to the next line; an FM (from) line indicates that after the given time, the weather will be what the line states; and a TEMPO line indicates that for period given the weather parameters in the line will happen for no more than 60 minutes of the hour, but the total periods will total no more than half the given period.

Trend

A Trend is a truncated version of a TAF giving the expected conditions in a two hour period following the issue of an observation. This short period forecast is appended to the end of a METAR.

METAR EGYM 291350Z 29010KT 8000 -RADZ FEW010 SCT037 OVC043 10/07 Q1008 BLU TEMPO 7000 -RADZ SCT020 WHT=

In this example the METAR indicates it is from EGYM (RAF Marham) at 1350 UTC on Day 29. The observation follows (see METAR for explanation), with the Trend added to the end of the observation.

The Trend reads TEMPO 7000 -RADZ SCT020 WHT i.e Temporary deterioration to 7 km visibility in slight rain or drizzle with scattered at 2000 ft, colour state White.

See also

*Colour State
*METAR
*Pilot Report
*Area forecast