AIM 

6/17/21 

1.  Type of Report. 

There are two types of TAF 

issuances, a routine forecast issuance (TAF) and an 
amended forecast (TAF AMD). An amended TAF is 
issued when the current TAF no longer adequately 
describes the on-going 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 communica-
tions header which precedes the actual forecasts. 

2.  ICAO Station Identifier. 

The TAF code 

uses ICAO 4

−

letter location identifiers as described 

in the METAR section. 

3.  Date and Time of Origin. 

This element is 

the 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.” 

4.  Valid Period Date and Time. 

The UTC 

valid period of the forecast consists of two four

−

digit 

sets, separated by a “/”. The first four

−

digit set is a 

two

−

digit date followed by the two

−

digit beginning 

hour, and the second four

−

digit set is a two

−

digit date 

followed by the two

−

digit ending hour. Although 

most airports have a 24

−

hour TAF, a select number of 

airports have a 30

−

hour TAF. 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 “AMD NOT SKED” added to the end of 
the forecasts. The time observations are scheduled to 
end and/or resume will be indicated by expanding the 
AMD NOT SKED statement. Expanded statements 
will include: 

(a) 

Observation ending time (AFT DDHH-

mm; for example, AFT 120200) 

(b) 

Scheduled observations resumption time 

(TIL DDHHmm; for example, TIL 171200Z) or 

(c) 

Period of observation unavailability 

(DDHH/DDHH); for example, 2502/2512). 

5.  Forecast Meteorological Conditions. 

This 

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

WIND/VISIBILITY/WEATHER/SKY CONDI-
TION/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 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. 

(a)  Wind. 

This five (or six) digit group 

includes the expected wind direction (first 3 digits) 
and speed (last 2 digits or 3 digits if 100 knots or 
greater). The contraction “KT” follows to denote the 
units of wind speed. Wind gusts are noted by the letter 
“G” appended to the wind speed followed by the 
highest expected gust. A variable wind direction is 
noted by “VRB” where the three digit direction 
usually appears. A calm wind (3 knots or less) is 
forecast as “00000KT.” 

EXAMPLE

−

 

18010KT . . . . .  

 wind 

one 

eight zero at one zero (wind is 

blowing from 180). 

35012G20KT  . .  wind three five zero at one two gust two 

zero. 

(b)  Visibility. 

The expected prevailing visi-

bility up to and including 6 miles is forecast in statute 
miles, including fractions of miles, followed by “SM” 
to note the units of measure. Expected visibilities 
greater than 6 miles are forecast as P6SM (plus 
six statute miles). 

EXAMPLE

−

 

1

/

2

SM 

−

 visibility one

−

half 

4SM 

−

 visibility four 

P6SM 

−

 visibility more than six 

(c)  Weather Phenomena. 

The expected 

weather phenomena is coded in TAF reports using the 
same format, qualifiers, and phenomena contractions 
as METAR reports (except UP). 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 
phenomena group is omitted for that time period. If, 
after a time period in which significant weather 
phenomena has been forecast, a change to a forecast 

7

−

1

−

68 

Meteorology