1. TAF production, amendment and planningby
Jannie Stander

2. OBJECTIVES OF THIS PRESENTATION
After this presentation you will be able to:
Understand the TAF format
Write a TAF in accordance with ICAO Annex 3, WMO-No.49, regional and national formats, codes and technical regulations on content, accuracy and timeliness.
Focus on significant weather changes according to SPECI conditions when writing your TAFs
Asses whether a TAF needs to be amended while monitoring current weather conditions

3. TAF FORMAT
TAF - Terminal Aerodrome Forecast. A TAF is a detailed forecast of expected weather elements at an aerodrome that significantly affects the movement of aircraft.
A TAF should give the best description of weather likely to affect the airfield during the specified forecast period, subject to agreed tolerances.
The specific value of any of the elements given in a forecast shall be understood by the recipient to be the most probable value which the element is likely to assume during the period of the forecast.
TAF messages follow the general form of a METAR.

4. TAF FORMAT THE AVIATION TAF CODE Wind direction ICAO designator
Date & time of issue
Date & time of validity
Wind speed
Wind gust
THE
AVIATION
TAF
CODE
Cloud amount and height
Horizontal
Visibility
Present weather
Vertical visibility
Cloud and Visibility OK
No Significant Weather
FC max temperature
Date & time of validity
Date & time of validity
FC min temperature
Probability and significant change groups
Date & time of change
Horizontal
Visibility
Wind direction
Wind speed
Wind gust
Cloud and Visibility OK
Cloud amount and height
Present weather
No Significant Weather
Vertical visibility
No Significant Weather

5. TAF FORMAT-EXAMPLE
TAF FAGG Z 2307/ KT 9999 BKN015 TEMPO 2307/2309 BKN005 FM KT 9999 BKN015 PROB30 TEMPO 2312/ RA BKN005 TX20/2312ZTN18/2307Z=
1) TAF Message indicator
2) ICAO LOCATOR
3) Time of issue
4) Time of validity
5) Forecast (Body of TAF) which includes prevailing base conditions and significant change/conditional change groups from the base conditions.
6) Temperature forecast

6. 1. TAF MESSAGE INDICATOR:
Routine forecast issuance (TAF) – As per normal issuance
Recommendation.— The period of validity of a routine TAF should be not less than 6 hours nor more than 30 hours; the period of validity should be determined by regional air navigation agreement. Routine TAF valid for less than 12 hours should be issued every 3 hours and those valid for 12 to 30 hours should be issued every 6 hours.
Amended forecast (TAF AMD) – Issued when expected or observed conditions meet amendment criteria for the specified forecast element, expected to persist; there is sufficient, reliable information on which the forecaster can base their judgment.
Corrected (TAF COR) – This is used when you have made a coding or typing error and corrections need to be made to the TAF

7. No observation (TAF CNL) – This is used when TAF’s cannot be kept under continuous review with all attempts failing.
Meteorological offices preparing TAF shall keep the forecasts under continuous review and, when necessary, shall issue amendments promptly.
The length of the forecast messages and the number of changes indicated in the forecast shall be kept to a minimum.

8. 2. ICAO LOCATOR Identified by four-letter ICAO station indicator
e.g. FALE Location indicator for King Shaka Airport.
TAF FALE Z 1912/2018 CNL=

9. 3. TIME OF ISSUE: Consist of a six-digit group (ddhhhh)
First two digits representing the day of the month (19th) (dd)
Last four digits represent time of issue in UTC/Z time (0600Z) (hhhh)
TAF’s valid for less than 12 hours are issued every 3 hours.
TAF’s valid for more than 12 hours are issued every 6 hours.
For Example:
TAF AMD FAJS Z 1912/2018 ….
TAF COR FALE Z 1912/2018 ….

10. 4. TIME OF VALIDITY: Consist of eight-digit group (ddhh/ddhh).
Remember to include the day of the month as well as the time in
UTC/Z.
Validity period is per regional air navigation agreement but must be between 6 and 30 hours inclusive.
Routine TAF valid for less than 12 hours should be issued every 3
hours and those valid for 12 to 30 hours should be issued every 6
hours.
Long term (FT TAFS, 24hour-30hour)
Short term (FC TAF, 6 to 11 hours)
For Example
TAF FAOR Z 1906/2012

11. 5. FORECAST(BODY OF THE TAF):
The body of the TAF includes gives the base prevailing conditions in terms of surface wind, visibility, weather (if any) and cloud (amount and ceiling)
It follows the same format as the METAR code
- TAF FAGG Z 2307/ KT 9999 BKN015 (This is the now cast part of the TAF where the METAR and remote sensing tools provide guidance) and can be viewed and the prevailing base conditions.
Change Groups and Conditional change groups (This is the forecast part of the TAF where NWP/RADAR/SAT and experience provide guidance)
TAF FAGG Z 2307/ KT 9999 SCT015 TEMPO 2307/2308 BKN005 FM KT 9999 BKN015 PROB30 TEMPO 2312/ RA BKN005 TX20/2312ZTN18/2307Z=

12. 6. Temperature Forecast (AMF AC 2.1.1)
It gives the expected maximum temperature (TX) and minimum temperature (TN) and the date and time of occurrence TX23/1912ZTN18/1918Z=
Recommendation.— When forecast temperatures are included in accordance with regional air navigation agreement, the maximum and minimum temperatures expected to occur during the period of validity of the TAF should be given, together with their corresponding times of occurrence.
Remember temperature is important because it effects air density and consequently the length of the runway needed for take off.

13. Change Groups (BECMG + FM)
Recommendation.— The change indicator “BECMG” and the associated time group should be used to describe 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.
The time period should normally not exceed 2 hours but in any case should not exceed 4 hours.
e.g. BECMG 1909/1911 BKN030: Condition is expected to change gradually between 09Z and 11Z to a broken cloud at 3000ft and this condition will prevail until any further change expected and this will be indicated by another set of change group or again BECMG.

14. FM (From)
Recommendation.— Where one set of prevailing weather conditions is expected to change significantly and more or less completely to a different set of conditions, the period of validity should be subdivided into self-contained periods using the abbreviation “FM” followed immediately by a four-figure time group in whole hours and minutes UTC indicating
FM is used to indicate rapid change expected, usually within less than one hour. When FM is used the TAF starts all over again and the order of a TAF should be followed

15. Probability (PROB)
The probability information should be placed after the element or elements forecast and be followed by the alternative value of the element or elements. The probability of a forecast of temporary fluctuations in meteorological conditions should be indicated, as necessary, by use of the abbreviation
Change groups PROB & TEMPO shall always be used together e.g. PROB40 TEMPO 1915/1918
Options are PROB30 TEMPO, PROB40 TEMPO or just TEMPO.
“PROB” followed by the probability in tens of per cent, placed before the change indicator “TEMPO” and associated time group.

16. Probability (PROB)
A probability of an alternative value or change of less than 30 per cent should not be considered sufficiently significant to be indicated.
A probability of an alternative value or change of 50 per cent or more, for aviation purposes should not be considered a probability but instead should be indicated, as necessary, by use of the change indicators “BECMG” or “TEMPO”.
Recommendation.— The number of change and probability groups should be kept to a minimum and should not normally exceed five groups.

17. Conditional Change Group Terms: Tempo
Recommendation.—
“TEMPO” should be used to describe expected frequent or infrequent temporary fluctuations in the meteorological conditions which reach or pass specified threshold values and last for a period of less than one hour in each instance and, in the aggregate, cover less than one-half of the forecast period during which the fluctuations are expected to occur.
If the temporary fluctuation is expected to last one hour or longer, the change group “BECMG” should be used.
It is therefore advisable that all convective precipitation be put under TEMPO (Showers and thundershowers) since it is temporary except for continuous rain resulting from Nimbostratus cloud.

18. Clouds in a TAF
When several layers of cloud are forecast, their amount and height of base should be included in the following order:
a) the lowest layer or mass regardless of amount, to be forecast as FEW, SCT, BKN or OVC as appropriate;
b) the next layer or mass covering more than 2/8, to be forecast as SCT, BKN or OVC as appropriate;
c) the next higher layer or mass covering more than 4/8, to be forecast as BKN or OVC as appropriate; and
d) cumulonimbus clouds, whenever forecast and not already included under a) to c).
Cloud information should be limited to cloud of operational significance; when no cloud of operational significance is forecast, and “CAVOK” is not appropriate, the abbreviation “NSC” should be used.
Remember low cloud bases and CB,s are hazards to aviation

19. How to write concise TAFs focusing on significant weather changes
In order to assist in flight planning TAFs should be concise and focus on significant weather conditions. These significant weather conditions are also used to amend the TAF.
Aerodrome meteorological offices preparing TAF shall keep the forecasts under continuous review and, when necessary, shall issue amendments promptly. The length of the forecast messages and the number of changes indicated in the forecast shall be kept to a minimum (ICAO ANNEX 3, latest addition).
TAF that cannot be kept under continuous review shall be cancelled ((ICAO ANNEX 3, latest addition).

20. Forecasting significant changes in Surface Wind and Direction
Recommendation.— In forecasting surface wind, the expected prevailing direction should be given.
When it is not possible to forecast a prevailing surface wind direction due to its expected variability, for example, during light wind conditions (less than 6 km/h (3 kt)) or thunderstorms, the forecast wind direction should be indicated as variable using “VRB”.
When the wind is forecast to be less than 2 km/h (1 kt), the forecast wind speed should be indicated as calm.
When the forecast maximum speed (gust) exceeds the forecast mean wind speed by 20 km/h (10 kt) or more, the forecast maximum wind speed should be indicated.
Remember surface direction and speed is important because it determines which runway is used.
When the surface wind is forecast to change through values of operational significance*
changes that require change in use of runway
Changes in runway tailwind/crosswind component through values representative of operating limits of typical aircraft using the airport. Threshold values to be set by Met Authority in consultations with ATS authority/operators
Ave wind speed change of ≥ 10kts 1
Variation between gusts and ave wind speed is ≥ 10kts
The ave wind speed before and or after being ≥ 15 kts 2
Ave wind direction change of ≥ 60° The ave wind speed before and or after being ≥ 10 3
When these significant changes in wind occur change the wind using BECMG or FROM in the TAF

21. Forecasting significant changes in values of horizontal visibility
The prevailing visibility should be forecast. When visibility is forecast to vary in different directions and the prevailing visibility cannot be forecast, the lowest forecast visibility should be given.
Recommendation.— When the visibility is forecast < than 800 m, it should be expressed in steps of 50 m;
when it is forecast to be >= 800 m but < than 5 km, in steps of 100 m;
>= 5 km but < than 10 km, in 1 kilometer steps;
and when it is forecast to be >= 10 km, it should be expressed as 9999, except when CAVOK conditions are forecast.
Remember any reduction in visibility/poor vis is a hazard to aviation
When the surface prevailing visibility is forecast to improve and change to, or pass through, one or more of the following values, or when that visibility is
forecast to deteriorate and pass through one or more of the following values:
150, 350, 600, 800, 1 500, m and 5000m

22. Horizontal visibility
The criteria for the indication of change groups (BECMG+FM) and/or preparation of amendments to TAF for SURFACE VISIBILITY are as follows
Horizontal visibility
Horizontal visibility is deteriorating AND passes through the following…
A deterioration
Using RVR
Runway Visual Range
150m
350m
600m
800m
800m
1500m
3000m
5000m
Horizontal visibility
Using eyes & visibility markers
An improvement
Horizontal visibility is improving AND changes to or passes through the following
RTC-PRE-004.2 22

23. Forecasting significant changes in weather
When any of the weather phenomena to the right is forecast to begin, end or change in intensity.
If significant weather as indicated in the main body of the TAF message is forecast to end, after the change group, the w’w’ group is replaced by NSW, the abbreviation for Nil Significant Weather.
Freezing (FZ) precipitation;
– Freezing fog;
– Moderate or heavy precipitation (including showers – SH);
– Low drifting (DR) dust, sand or snow;
– Blowing (BL) dust, sand or snow;
– Duststorm (DS);
– Sandstorm (SS);
– Thunderstorm (TS);
– Squall (SQ);
– Funnel cloud (tornado or waterspout – FC);
– Other weather phenomena given in Code table 4678 which are expected to cause a significant change in visibility.
When these significant changes in weather phenomena occur they need to be forecast using BECMG or FROM in the TAF

24. Present weather – (the start or cessation of)
The criteria for the indication of change groups (BECMG+FM) and/or preparation of amendments to TAF for WEATHER are as follows
Present weather – (the start or cessation of)
marked by the advance
of a “wall of dust”
up to 3000m high
including showers
with or without precipitation
Moderate Heavy precipitation FC TS
course sand particles
up to a max of 20–30m
a sudden increase in wind speed
of at least 16 kts
with a new speed of at least 22 kts
and lasting for at least 1 minute
raised by the wind
to more than 2m agl
BLDU
BLSA
BLSN
raised by the wind
to less than 2m agl SQ DS SS
FZRA
FZFG
DRDU
DRSA
DRSN
Surface temperature must be < 0 °C for precipitation or fog to freeze on contact with the surface.

25. Forecasting significant changes in cloud amount
Cloud amount in a TAF will be reported as FEW(0-2) oktas; Scattered (SCT, 3-4 oktas); Broken (BKN, 5-7 oktas); Overcast (OVC, 8 oktas).
Type of the cloud is only mentioned if it is a TCU or Cumulonimbus cloud (Cb)
Recommendation.— Cloud amount should be forecast using the abbreviations “FEW”, “SCT”, “BKN” or “OVC” as necessary.
When the amount of a cloud layer or mass of cloud below 450 m (1 500 ft) is forecast to change
– from SCT or FEW, increasing to BKN or OVC or
– from BKN or OVC, decreasing to SCT or FEW.
When cumulonimbus clouds are expected to develop or dissipate.
When these significant changes in cloud height occur they need to be forecast using BECMG or FROM in the TAF

26. Cloud cover 7/8 6/8 5/8 8/8 BKN OVC SCT or less BKN or OVC or from
4/8
SCT or less BKN or OVC
or from
OVC or BKN SCT or less
Cloud cover changes from … … …
Cloud base ≤ 1500 ft

27. Forecasting significant changes in cloud height
When the height of the base of the lowest layer or mass of cloud covering 5/8 or more (BKN or OVC) is forecast to lift and change to, or pass through, one or
more of the following values or to lower and pass through one or more of the following values:
0, 60, 150 or 300 m (or 100, 200, 500 or ft), 1500ft added due to visual flight rules
When these significant changes in cloud height occur they need to be forecast using BECMG or FROM in the TAF

28. Temperature Cloud height
along with Cloud cover of BKN or OVC
Cloud height
TEMP An increase of ≥ 2°C at any given point in time
1500ft
1500ft
Cloud height lifting or improving AND changes to or passing through
Cloud height lowering or deteriorating AND passing through
1000ft
1000ft
500ft
500ft
200ft
200ft
100ft
100ft
Earth’s surface

29. Forecasting significant changes in cloud height
When vertical visibility is forecast to improve and change to, or pass through,
one or more of the following values, or to deteriorate and pass through one or
more of the following values:
30, 60, 150 or 300 m (100, 200, 500 or ft)
When these significant changes in cloud height and amount occur they need to be forecast in a BECMG or FROM in the TAF

30. Example TAF
FAOR Z 2112/ KT CAVOK BECMG 2119/ KT BECMG 2123/2201 BKN010 BECMG 2200/ KT TEMPO 2201/ BR BKN005 PROB30 TEMPO 2203/ FG OVC001 BECMG 2208/ KT BKN015 BECMG 2210/2212 SCT030 TX19/2112ZTN06/2204Z=

31. TAF Flight planning TYPE OF FORECAST AREA AIRSPACE COVERED
STAGE OF FLIGHT PLANNING
VALIDITY PERIOD OR FIXED TIME
RESPONSIBILITY
AMF Competency addressed
TAF
Aerodrome
Pre and In flight
From 6 to 30 Hours Inclusive
Aviation Meteorological Office (AMO)
AMF Competency 2:
Wind, Visibility, Temp, cloud (humidity) cloud base and cloud type, precipitation onset and duration and associated visibilities

32. Thank you