Aviation Weather Training

Aviation Weather Training

Aviation Training / December 11, 2019

A Terminal Aerodrome Forecast (TAF) is a concise statement of the expected meteorological conditions at an airport during a specified period (usually 24 hours). Each ICAO state may modify the code as needed. The TAF code, as described here, is the one used in the United States. TAFs use the same weather code found in METAR weather reports.

TAF Report Elements

A TAF report contains the following sequence of elements in the following order:

The international TAF also contains forecast temperature, icing, and turbulence. These three elements are not included in National Weather Service (NWS) prepared TAFs. The U.S. has no requirement to forecast temperatures in an aerodrome forecast and the NWS will continue to forecast icing and turbulence in AIRMETs and SIGMETs.

Type of Report: ie. (TAF)

The report type header will always appear as the first element in the TAF forecast. There are two types of TAF reports, a routine forecast, TAF, and an amended forecast, TAF AMD. An amended TAF is issued when the current TAF no longer adequately describes the ongoing weather or the forecaster feels the TAF is not representative of the current or expected weather.

Corrected (COR) or delayed (RTD) TAFs are identified only in the communications header which precedes the forecast text.

ICAO Station Identifier: ie. (KOKC)

The TAF code uses the ICAO four-letter location identifiers. In the conterminous United States, the three-letter identifier is prefixed with a K. For example SEA (Seattle) becomes KSEA. Elsewhere, the first one or two letters of the ICAO identifier indicate in which region of the world and country (or state) the station is. Pacific locations such as Alaska, Hawaii, and the Marianas islands start with P followed by an A, H, or G respectively. The last two letters reflect the specific station identification. If the location's three-letter identification begins with an A, H, or G, the P is just added to the beginning. If the location's three-letter identification does not begin with an A, H, or G, the last letter is dropped and the P is added to the beginning.

Examples:

ANC (Anchorage, AK) becomes PANC
OME (Nome, AK) becomes PAOM
HNL (Honolulu, HI) becomes PHNL
KOA (Keahole Point, HI) becomes PHKO
GRO (Rota Becomesland) becomes PGRO
UAM (Anderson AFB) becomes PGUA

Canadian station identifiers start with C. Mexican and western Caribbean station identifiers start with M. The identifier for the eastern Caribbean is T, followed by the individual country's letter.

Date and Time of Origin: ie. (051130Z)

This element is the UTC date and time the forecast is actually prepared. The format is a two-digit date and four-digit time followed, without a space, by the letter Z. Routine TAFs are prepared and filed approximately one-half hour prior to scheduled issuance times. TAFs are scheduled for issuance foure times daily at 0000Z, 0600Z, 1200Z, and 1800Z.

Example:

091050Z - Forecast prepared on the ninth day of the month at 1050Z.

Valid Period Date and Time: ie. (051212)

The UTC valid period of the forecast is a two-digit date followed by the two-digit beginning hour and two-digit ending hour. Routine TAFs are valid for 24-hours. Valid periods beginning at 0000Z shall be indicated as 00. Valid periods ending at 0000Z shall be indicated as 24. The 24 indication applies to all time group ending times.

In the case of an amended forecast, or a forecast which is corrected or delayed, the valid period may be for less than 24 hours. Where an airport or terminal operates on a part-time basis (less than 24 hours/day) the TAFs issued for those locations will have the abbreviated statement NIL AMD SKED AFT (closing time)Z, added to the end of the forecast. For the TAFS issued while these locations are closed, the word NIL will appear in place of the forecast text. A delayed (RTD) forecast will then be issued for these locations after two complete observations are received.

091212 - Forecast valid from the ninth at 1200Z til the tenth at 1200Z.
110024 - Forecast valid from the eleventh at 0000Z till the twelfth at 0000Z.
010524 - Amended forecast valid from the first at 0500Z till the second at 0000Z.

This is the body of the TAF. The basic format is:

Wind - Visibility - Weather - Sky Condition - Optional Data (Wind Shear)

The wind, visibility, and sky condition elements are always included in the initial time group of the forecast. Weather is included in the initial time group only if significant to aviation. If a significant, lasting change in any of the elements is expected during the valid period, a new time period with changes is included. It should be noted that, with the exception of a FM group, the new time period will include only those elements which are expected to change; i.e., if a lowering of the visibility is expected but the wind is expected to remain the same, the new time period reflecting the lower visibility would not include a forecast wind. The forecast wind would remain the same as in the previous time period.

Any temporary conditions expected during a specific time period are included with that time period.

Wind: ie. (14008KT)

The wind group includes forecast surface winds. The surface wind is the expected wind direction (first three digits) and speed (last two or three digits if 100 knots or greater). The contraction KT follows to denote the units of wind speed in knots. Wind gusts are noted by the letter G appended to the wind speed followed by the highest expected gust (two or three digits if 100 knots or greater).

Calm winds (three knots or less) are encoded as 00000KT.

Variable winds are encoded when it is impossible to forecast a wind direction due to winds associated with convective activity or low wind speeds. A variable wind direction is noted by VRB where the three digit direction usually appears.

18010KT - Wind one eight zero at one zero knots
to note the units of measure. Statute miles followed by fractions of statute miles are separated with a space, for example, 1 1/2SM. Forecast visibility greater than 6 statute miles is indicated by coding P6SM. Directional or variable visibility is not forecasted and the visibility group is omitted if missing.

1/2SM - Visibility one-half statute mile
2 1/4SM - Visibility two and one-quarter statute miles
5SM - Visibility five statute miles
P6SM - Visibility more than six statute miles

Weather: ie. (BR)

The expected weather phenomenon or phenomena is coded in TAF reports using the same format, qualifiers, and phenomena contractions as METAR reports (except UP).

Qualifiers of Intensity or Proximity