A terminal aerodrome forecast is a report established for the 5 statute mile radius around an airport. TAF reports are usually given for larger airports. Each TAF is valid for a 24-hour time period, and is updated four times a day at 0000Z, 0600Z, 1200Z, and 1800Z. The TAF utilizes the same descriptors and abbreviations as used in the METAR report.
The terminal forecast includes the following information in sequential order:
1. Type of Report A TAF can be either a routine forecast (TAF) or an amended forecast (TAF AMD).
2. ICAO Station Identifier The station identifier is the same as that used in a METAR.
3. Date and Time of Origin Time and date of TAF origination is given in the six-number code with the first two being the date, the last four being the time. Time is always given in UTC as denoted by the Z following the number group.
4. Valid Period Date and Time The valid forecast time period is given by a six-digit number group. The first two numbers indicate the date, followed by the two-digit beginning time for the valid period, and the last two digits are the ending time.
5. Forecast Wind The wind direction and speed forecast are given in a five-digit number group. The first three indicate the direction of the wind in reference to true north. The last two digits state the windspeed in knots as denoted by the letters “KT.” Like the METAR, winds greater than 99 knots are given in three digits.
6. Forecast Visibility The forecast visibility is given in statute miles and may be in whole numbers or fractions. If the forecast is greater than 6 miles, it will be coded as “P6SM.”
7. Forecast Significant Weather Weather phenomenon is coded in the TAF reports in the same format as the METAR. If no significant weather is expected during the forecast time period, the denotation “NSW” will be included in the “becoming” or “temporary” weather groups.
8. Forecast Sky Condition Forecast sky con- ditions are given in the same manner as the METAR. Only cumulonimbus (CB) clouds are forecast in this portion of the TAF report as opposed to CBs and towering cumulus in the METAR.
9. Forecast Change Group For any significant weather change forecast to occur during the TAF time period, the expected conditions and time period are included in this group. This information may be shown as From (FM), Becoming (BECMG), and Temporary (TEMPO). “From” is used when a rapid and significant change, usually within an hour, is expected. “Becoming” is used when a gradual change in the weather is expected over a period of no more than 2 hours. “Temporary” is used for temporary fluctuations of weather, expected to last for less than an hour.
10. Probability Forecast The probability forecast is given percentage that describes the probability of thunderstorms and precipitation occurring in the coming hours. This forecast is not used for the first 6 hours of the 24-hour forecast.
The period of validity should not be less than 6 HRs, no more than 30 HRs.
TAFs valid for less than 12 HRs should be issued every 3 HRs and those valid for 12 to 30 HRs every 6 HRs.
Application of initial part of TAF
(a) Applicable time period
From the start of the TAF validity period up to the time of applicability of the first subsequent “FM….” or “BECMG” or, if no “FM….” or “BECMG” is given, up to the end of the validity period of the TAF.
(b) Application of forecast
The prevailing weather conditions forecast in the initial part of the TAF should be fully applied with the exception of the mean wind and gusts (and crosswind) which should be applied in accordance with the policy in the column “BECMG AT” and “FM….” in the table on the next page. This may, however, be overruled temporarily by a “TEMPO” or “PROB” if applicable, according to the table on the next page.
|BECMG (becoming)||Changes where the meteorological conditions are expected to reach or pass through specified threshold values at a regular or irregular rate and at an unspecified time during the time period (starting 2300Z on the 8th day and ending at 0100Z on the 9th day).
Example TAF – FT:
NZZO 081140Z 0812/0918 VRB02KT 1800 BR BECMG 0823/0901 00000KT 0500 FG VV002
|TEMPO (temporary)||Describes expected frequent or infrequent temporary fluctuations in meteorological conditions which reach or pass specified threshold values and last for a period of less then 1 hour in each instance and in the aggregate, cover less than half of the fluctuation period (from 1800Z on the 8th day to 2300Z on the 8th day).
Example TAF – FC:
LFPG 081140Z 0812/0918 29010KT 5000 NSW TEMPO 0818/0823 1500 SHSN =
|PROB (probability)||Probability in percent of occurrence of an alternative weather development and the time period (from 1000Z on the 9th day to 1200Z on the 9th day). PROB30/40 alone or in combination with TEMPO are used.
Example TAF – FT 18/24:
VAAB 081140Z 0812/0918 26018KT 3000 RA SCT012 BKN030 PROB40 0910/0912 25028G40+RA =
|Time Divider FM (from)||Where one set of prevailing weather condition is expected to change significantly and more or less completely to a different set of conditions, the period of validity should be subdivided into a self-contained period giving the time group in whole hour and minutes UTC when the change is expected to occur (at 1000Z on the 9th day). The period following from should be self-contained and all forecast conditions given before should be superseded.
Example TAF – FT:
KBGR 081140Z 0812/0918 35008KT P6SM SCT200 FM091000 03005KT P6SM BKN120 =
|Optional Groups in TAF|
|Turbulence||Coded 6-figure group
1st figure: Group indicator 5
2nd figure: Type of turbulence
0 = none
1 = light 2 = moderate in clear air, infrequent
3 = moderate in clear air, frequent
4 = moderate in cloud, infrequent
5 = moderate in cloud, frequent
6 = severe in clear air, infrequent
7 = severe in clear air, frequent
8 = severe in cloud, infrequent
9 = severe in cloud, frequent
X = extreme (US AFB TAF only)
3rd to 5th figure: Height of lowest turbulence level in hundreds of feet above aerodrome elevation.
6th figure: Thickness of turbulent layer in thousands of feet; exception: 0 = top of clouds
Example: 590200 = severe in cloud, frequent, from 2000ft up to top of cloud.
|Icing||Coded 6-figure group
1st figure: Group indicator 6
2nd figure: Type of icing
0 = none
1 = light
2 = light in cloud
3 = light in precipitation
4 = moderate
5 = moderate in cloud
6 = moderate in precipitation
7 = severe
8 = severe in cloud
9 = severe in precipitation
3rd to 5th figure: Height of lowest icing level in hundreds of feet above aerodrome elevation.
6th figure: Thickness of icing layer in thousands of feet; exception: 0 = top of cloud
Example: 660083 = moderate in precipitation, from 800 upwards in layer 3000ft thick.
Source: ICAO, FAA