An Aerodrome Forecast (TAF) is a concise statement of the expected meteorological conditions at an airport during a specified period (usually 24 hours). Each country is allowed to make modifications or exceptions to the code for use in each particular country. 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. Detailed explanations of weather coding is found only in the METAR sections of this workbook.
TAF
KOKC 051130Z 051212 14008KT 5SM BR BKN030 TEMPO 1316 1 1/2SM BR
FM1600 16010KT P6SM NSW SKC BECMG 2224 20013G20KT
4SM SHRA OVC020 PROB40 0006 2SM TSRA OVC008CB
BECMG 0608 21015KT P6SM NSW SCT040
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 NWS prepared TAF's, and therefore will not be covered in this manual.
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.
The following paragraphs describe the elements in a TAF report. A sample TAF report will accompany each paragraph with the subject element highlighted.
TAF
KOKC 051130Z 051212 14008KT 5SM BR BKN030 TEMPO 1316 1 1/2SM BR
FM1600 16010KT P6SM SKC BECMG 2224 20013G20KT
4SM SHRA OVC020 PROB40 0006 2SM TSRA OVC008CB
BECMG 0608 21015KT P6SM NSW SCT040 =
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. The communications header is not displayed when the TAF report is retrieved by the specialist.
Example: TAF - terminal forecast TAF AMD - amended terminal forecast
TAF
KOKC 051130Z 051212 14008KT 5SM BR BKN030 TEMPO 1316 1 1/2SM BR
FM1600 16010KT P6SM SKC BECMG 2224 20013G20KT
4SM SHRA OVC020 PROB40 0006 2SM TSRA OVC008CB
BECMG 0608 21015KT P6SM NSW SCT040 =
The TAF code uses ICAO four-letter location identifiers as described in the METAR section.
TAF
KOKC 051130Z 051212 14008KT 5SM BR BKN030 TEMPO 1316 1 1/2SM BR
FM1600 16010KT P6SM SKC BECMG 2224 20013G20KT
4SM SHRA OVC020 PROB40 0006 2SM TSRA OVC008CB
BECMG 0608 21015KT P6SM NSW SCT040 =
This element is the UTC date and time the forecast is actually prepared. The format is a twodigit 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 four times daily at 0000Z, 0600Z, 1200Z, and 1800Z.
Example: 091050Z - Forecast prepared on the ninth day of the month at 1050Z
TAF
KOKC 051130Z 051212 14008KT 5SM BR BKN030 TEMPO 1316 1 1/2SM BR
FM1600 16010KT P6SM SKC BECMG 2224 20013G20KT
4SM SHRA OVC020 PROB40 0006 2SM TSRA OVC008CB
BECMG 0608 21015KT P6SM NSW SCT040 =
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.
Example:
091212 - Forecast valid from the ninth at 1200Z till the tenth at
1200Z.
110024 - Forecast valid from the eleventh at 0000Z till the twelfth
at 0000Z.
(not 110000 or 112400)
010524 Amended forecast valid from the first at 0500Z till the
second at 0000Z.
TAF
KOKC 051130Z 051212 14008KT 5SM BR BKN030 TEMPO 1316 1 1/2SM BR
FM1600 16010KT P6SM SKC BECMG 2224 20013G20KT
4SM SHRA OVC020 PROB40 0006 2SM TSRA OVC008CB
BECMG 0608 21015KT P6SM NSW SCT040 =
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 the 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. The following describes the elements in the above format.
The wind group includes forecast surface winds. The surface wind forecast 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.
Example:
18010KT - "Wind one eight zero at one zero"
35012G20KT - "Wind three five zero at one two gust two
zero"
00000KT - "Wind calm"
VRB16G28KT - "Wind variable at one six gust two eight"
The expected prevailing visibility is forecast in statute miles and fractions of statute miles followed by SM 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.
Example: 1/2SM - "Visibility one-half" 2 1/4SM - "Visibility two and one-quarter" 5SM - "Visibility five" P6SM - "Visibility more than six"
Although not used in the U.S., the contraction "CAVOK" (ceiling and visibility OK) replaces visibility, weather, and sky condition if:
The expected weather phenomenon or phenomena is coded in TAF reports using the same format, qualifiers, and phenomena contractions as METAR reports (except UP). Weather code is found in the METAR Section.
Obscurations to vision will be forecast whenever the prevailing visibility is forecast to be 6 statute miles or less.
If no significant weather is expected to occur during a specific time period in the forecast, the weather group is omitted for that time period. If, after a time period in which significant weather has been forecast, a change to a forecast of no significant weather occurs, the contraction, NSW (No Significant Weather) will appear as the weather group in the new time period. However, NSW is only included in BECMG or TEMPO groups.
TAF sky condition forecasts use the METAR format described in METAR Section. Cumulonimbus clouds (CB) are the only cloud type forecast in TAFs.
When the sky is obscured due to a surfaced-based phenomenon, vertical visibility (VV) into the obscuration is forecast. The format for vertical visibility is "VV" followed by a three-digit height in hundreds of feet.
Note: Ceiling layers are not designated in the TAF code. For aviation purposes, the ceiling is the lowest broken or overcast layer or vertical visibility into a complete obscuration.
Example:
SKC - "Sky clear"
SCT005 BKN025CB BKN250 - "Five hundred scattered, ceiling two
thousand five hundred broken
cumulonimbus clouds, two five
thousand broken"
VV008 - "Indefinite ceiling eight hundred"
Wind shear is the forecast of non-convective low level winds (up to 2000 feet) and is entered after the sky conditions when wind shear is expected. The forecast includes the height of the wind shear followed by the wind direction and wind speed at the indicated height. Height is given in hundreds of feet AGL up to and including 2,000 feet. Wind shear is encoded with the contraction, WS, followed by a three-digit height, slant character "/," and winds at the height indicated in the same format as surface winds. The wind shear element is omitted if not expected to occur.
Example:
WS010/18040KT - "Low level wind shear at one thousand,
wind one eight zero at four zero"
Other items not included in domestic TAF reports that may appear in international or some military reports as optional data following wind shear are:
The probability or chance of thunderstorms or other precipitation events occurring, along with associated weather conditions (wind, visibility, and sky conditions).
TAF
KOKC 051130Z 051212 14008KT 5SM BR BKN030 TEMPO 1316 1 1/2SM BR
FM1600 16010KT P6SM SKC BECMG 2224 20013G20KT
4SM SHRA OVC020 PROB40 0006 2SM TSRA OVC008CB
BECMG 0608 21015KT P6SM NSW SCT040 =
The PROB40 group is used when the occurrence of thunderstorms or precipitation is in the 30% to less than 50% range, thus the probability value 40 is appended to the PROB contraction. This is followed by a four-digit group giving the beginning hour and ending hour of the time period during which the thunderstorms or precipitation is expected.
Note: PROB40 will not be shown during the first six hours of a forecast.
Example:
PROB40 2102 1/2SM +TSRA - "Chance between 2100Z and 0200Z of
visibility one-half thunderstorm, heavy
rain"
PROB40 1014 1SM RASN - "Chance between 1000Z and 1400Z of
visibility one rain and snow"
PROB40 2024 2SM FZRA - "Chance between 2000Z and 0000Z of
visibility two freezing rain"
The following change indicators are used when either a rapid, gradual, or temporary change is expected in some or all of the forecast meteorological conditions. Each change indicator marks a time group within the TAF report.
TAF
KOKC 051130Z 051212 14008KT 5SM BR BKN030 TEMPO 1316 1 1/2SM BR
FM1600 16010KT P6SM SKC BECMG 2224 20013G20KT
4SM SHRA OVC020 PROB40 0006 2SM TSRA OVC008CB
BECMG 0608 21015KT P6SM NSW SCT040 =
The FM group is used when a rapid change, usually occuring in less than one hour, in prevailing conditions is expected. Typically, a rapid change of prevailing conditions to more or less a completely new set of prevailing conditions is associated with a synoptic feature passing through the terminal area (cold or warm frontal passage). Appended to the FM indicator is the four-digit hour and minute the change is expected to begin and continues until the next change group or until the end of the current forecast.
A FM group will mark the beginning of a new line in a TAF report. Each FM group contains all the required elements -- wind, visibility, weather, and sky condition. Weather will be omitted in FM groups when it is not significant to aviation. FM groups will not include the contraction NSW.
Example:
FM0100 SKC - "After 0100Z sky clear"
FM1430 OVC020 - "After 1430Z ceiling two thousand
overcast"
TAF
KOKC 051130Z 051212 14008KT 5SM BR BKN030 TEMPO 1316 1 1/2SM BR
FM1600 16010KT P6SM SKC BECMG 2224 20013G20KT
4SM SHRA OVC020 PROB40 0006 2SM TSRA OVC008CB
BECMG 0608 21015KT P6SM NSW SCT040 =
The BECMG group is used when a gradual change in conditions is expected over a longer time period, usually two hours. The time period when the change is expected is a four-digit group with the beginning hour and ending hour of the change period which follows the BECMG indicator. The gradual change will occur at an unspecified time within this time period. Only the changing forecast meteorological conditions are included in BECMG groups. The omitted conditions are carried over from the previous time group.
Example:
OVC012 BECMG 1416 BKN020 - "Ceiling one thousand two
hundred overcast. Then a
gradual change to ceiling two
thousand broken between 1400Z
and 1600Z"
TAF
KOKC 051130Z 051212 14008KT 5SM BR BKN030 TEMPO 1316 1 1/2SM BR
FM1600 16010KT P6SM SKC BECMG 2224 20013G20KT
4SM SHRA OVC020 PROB40 0006 2SM TSRA OVC008CB
BECMG 0608 21015KT P6SM NSW SCT040 =
The TEMPO group is used for any conditions in wind, visibility, weather, or sky condition which are expected to last for generally less than an hour at a time (occasional), and are expected to occur during less than half the time period. The TEMPO indicator is followed by a four-digit group giving the beginning hour and ending hour of the time period during which the temporary conditions are expected. Only the changing forecast meteorological conditions are included in TEMPO groups. The omitted conditions are carried over from the previous time group.
Example:
SCT030 TEMPO 1923 BKN030 - "Three thousand scattered with
occasional ceilings three
thousand broken between 1900Z
and 2300Z."
4SM HZ TEMPO 0006 2SM BR HZ - "Visibility four in haze with
occasional visibility two in
mist and haze between 0000Z and
0600Z."
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