Aviation Meteorology - Terminal Aerodrome Forecasts

Terminal Aerodrome Forescasts (TAF)CAHIT KUTAY UYSAL S004992

OUTLINE What is TAF?

Decoding TAF

Type of Report

ICAO Station Identifier

Date and Time of Origin

Valid Period Date and Time

Forecast Meteorological Conditions

Wind

Visibility

Weather

Clouds Coverage

Forecast Change Indicators

The From (FM) Gruop

The Becoming (BECMG) Group

The Temporary (TEMPO) Group

The Probability (PROB) Indicator

End of Message

Bibliography

What is TAF?• Basically, TAF is a forecast of the weather for a specified aerodrome, over a definied period of time.• TAF’s coding system is very similar with METAR’s coding system. Many of the coding groups idential in

both the METAR and TAF. • As a basis, TAF reports can transmit in short and long period.

• At the same time, some major airports issue TAFs covering of 30 hours to meet the operational requirements of international carriers.

• Short Periot(9-12 Hours) TAFs are issued every 3 hours, Long Period (18-30 Hours) TAFs every 6 hours.

Decoding TAF A TAF report contains the following sequence of elements in the following order.

1. Type of Report

2. ICAO Station Identifier

3. Date and Time of Origin

4. Valid Period Date and Time

5. Forecast Meteorological Conditions

Decoding TAF Istanbul Ataturk Airport’s 10 October 2015 TAF;

TAF LTBA 100440Z 1006/1112 04009KT CAVOK

TEMPO 1006/1010 SCT030

PROB30 1101/1105 4000 BR SCT010

BECMG 1105/1108 SCT030 BKN100=

Type of Report• 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.• Our example is a routine forecast; TAF LTBA 100440Z 1006/1112 04009KT CAVOK

TEMPO 1006/1010 SCT030 PROB30 1101/1105 4000 BR SCT010 BECMG 1105/1108 SCT030 BKN100=Amendment Forecasts; • When a TAF requires an amendment, the amended forecast may be indicated by the code AMD,

highlighted in red, after the TAF identifier, as shown below;

TAF AMD LTBA 100440Z 1006/1112 04009KT CAVOK TEMPO 1006/1010 SCT030 PROB30 1101/1105 4000 BR SCT010 BECMG 1105/1108 SCT030 BKN100=

ICAO Station Identifier The TAF code uses the ICAO four letter location identifier.

TAF LTBA 100440Z 1006/1112 04009KT CAVOK TEMPO 1006/1010 SCT030 PROB30 1101/1105 4000 BR SCT010 BECMG 1105/1108 SCT030 BKN100=

In our example; LTBA is the Istanbul Ataturk Airport’s ICAO four letter code

Date and Time of Origin• In the TAF, there are two items of date-time information.

•The first group indicates the date and timeat which the TAF issued.


• 100440Z the digits 10 identify the day of the month. Other 4-digit and Z indicates hours and minutes in UTC. The above TAF, originates on 10th day of the month, at 04:00, UTC.

Valid Period Date and Time TAF LTBA 100440Z 1006/1112 04009KT CAVOK

TEMPO 1006/1010 SCT030 PROB30 1101/1105 4000 BR SCT010 BECMG 1105/1108 SCT030 BKN100=

• The next code-group identifies the period of validity of the TAF. The day of month is repeated, 10, and is followed by the start of the forecast time in hours, 06, and then, seperated by a slash the end of the forecast time, with the validation day of the month, 11, and end of the validity period in hours, 12.

Forecast Meteorological Conditions• This is body of the TAF. The basic format is;

• Wind – Visibility – Weather – Sky Condition – Optional Data

Wind• The next item in the TAF is the observed wind information.


• Firstly, the direction of the wind given in degrees true. In this example, wind comes from 040 degree.

• The other 2 digit and KT are the wind speed in knot. In this example, wind speed is 09 Knot.

• Also, If wind comes from every direction, it shown with VRB (variable). Example, TAF LTBA 100440Z 1006/1112 VRB09KT=

Visibility• Visibility in TAF is represented by the next group which is depicted in red below.

• TAF LTBA 100440Z 1006/1112 04009KT 6000=

• In TAF reports, up to 10km, the visibility is measured in metres. In example, 6000 means that

the prevailing visibility is 6000 metres.

• Once the visibility reaches 10 km or more, the code figure used is 9999.

• Visibility of less than 50 metres is indicated by the code 0000.

Weather• The expected phenomenon or phenomena is coded in TAF reports after visibility. There are some codes with their decodes;

Qualifiers of Intensity or Proximity

- Light

(No Qualifier) Moderate

+ Heavy

VC In the Vicinity

WeatherQualifier Descriptor

MI Shallow

BC Patches

DR Low Drifting

BL Blowing

SH Shower

TS Thunderstorm

FZ Freezing

PR Partial

WeatherPrecipitation

DZ Drizzle

RA Rain

SN Snow

SG Snow Grains

IC Ice Crystals

PL Ice Pellets

GR Hail

GS Small Hail or Snow Pellets

UP Unknown Precipitation

WeatherObscuration

BR Mist

FG Fog

FU Smoke

DU Dust

SA Sand

HZ Haze

PY Sprey

VA Volcanic Ash

WeatherOthers

PO Well-Developed Dust/Sand Whirls

SQ Squalls

FC Funnel Cloud

+FC Well-Developed Funnel Cloud, Tornado or Waterspout

SS Sandstorm

DS Duststorm

Weather CAVOK Code

◦ TAF LTBA 100440Z 1006/1112 04009KT CAVOK=

• The code CAVOK is frequently used in the TAF code, being the abbreviation for ‘Ceiling (or cloud) and

visibility are OK’. If CAVOK is used, it will replace the visibiliy, RVR, weather and cloud groups. There are four

criteria which must be met in order for CAVOK to appear in the TAF. These are;

1. The visibility must be 10 kilometres or more.

2. The height of the lowest cloud must be no less than 5000 feet, or the level of highest minimum sector

altitude, whichever is the greater.

3. There must be no cumulonimbus present.

4. There must be no significant weather.

Clouds Coverage• After the wetaher information, there are a new code group which give details of cloud coverage, as highlighted in red.• TAF LTBA 100440Z 1006/1112 04009KT CAVOK TEMPO 1006/1010 SCT030 PROB30 1101/1105 4000 BR SCT010 BECMG 1105/1108 SCT030 BKN100=

◦ There are several prefixes which are used to describe cloud amount, at any given level. Cloud coverage is reported in the TAF using the following three-letter codes:

1. SKC (SKY CLEAR) meaning no cloud coverage2. FEW (FEW) meaning 1/8 - 2/8 of cloud coverage3. SCT (SCATTERED) meaning 3/8 – 4/8 of cloud coverage4. BKN (BROKEN) meaning 5/8 – 7/8 of cloud coverage5. OVC (OVERCAST) meaning complete cloud coverage .

Clouds CoverageTAF LTBA 100440Z 1006/1112 04009KT CAVOKTEMPO 1006/1010 SCT030PROB30 1101/1105 4000 BR SCT010BECMG 1105/1108 SCT030 BKN100=

◦ Cloud base is given as a three-digit figure showing hunfreds of feet. Cloud base in a TAF is always measured as height above aerodrome level, using the current aerodrome QFE.

◦ In this example (SCT030) SCT cloud’s height is 3000 feet. ◦ It will change and Scattered clouds base decrease to 1000 feet.◦ The last one, SCT will get old position(3000 feet) and BKN clouds will be 10000 feet.

Forecast Change Indicators• There are distinctive TAF codes which indicate that a change is expected in some or all of the

forecast meteorological conditions.

• The nature of the change can vary; it may, for instance, be a rapid, gradual or temporary

change.

• These codes are FM (meaning FROM), BECMG (meaning BECOMING), TEMPO (meaning

TEMPORARILY), and PROB (meaning PROBABILITY).

The From (FM) Group• The FM indicator introduces what is effectively a new forecast.

• The change indicator FM is followed by a four-digit time group in hours, and minutes, to indicate the time at which the change is expected to begin.

• For instance,• TAF LTBA 13060Z 1307/1316 31015KT 8000 –SHRA SCT010 BKN018 FM 1220 27017KT 4000 BKN010=In these example above, highlighted in red, we read that from 1220Z until the end of the TAF period, the wind will change to be 270 degree at 17 knots, with a prevailing visibility of 4000 metres, and broken cloud at 1000 feet.

The Becoming (BECMG) Group• The code BECMG, marks a permanent change in the forecast weather, but which will establish

itself more gradually than weather conditions introduced by the code FM.

• TAF LTBA 130600Z 1307/1316 31015KT 8000 –SHRA SCT010 BKN018 BECMG 0911 5000 –RA=

• At the example, TAF indicates that at some time between the 0900 UTC and 1100 UTC, but

definetely by 1100 UTC the prevailing conditions will give 5000 metres visibility, in light rain.

There is no new wind informatşon after BECMG, so the implication is that the wind will be as

previously forecast: 310 degree at 15 knots.

The Temporary (TEMPO) Group• The code TEMPO introduces a temporary change in weather conditions, expected to last for less than one hour.

• Changes will occur at any time within the specified time period, but it is expected to less than onehour each time, and, in aggregate, will last no longer than half time the time period of complete forecast.

• The TEMPO indicator is followed by a 4-digit time group indicating the hours between which the temporary conditions are expected to begin and end.

• TAF LTBA 130600Z 1307/1316 31015KT 8000 KT –SHRA SCT010 BKN018 TEMPO 1214 4000 TSRA BKN010CB=

• At this example, TAF tells us that sometime between 1200 UTC and 1400 UTC, the visibility will fall 4000 metres, with the weather being thunderstorms and moderate rain. There will be 5 – 7 oktas of cumulonimbus cloud at 1000 feet. However, after 1400 UTC, the weather will return to the conditions specified in the first part of message.

The Probability (PROB) Indicator• The code PROB in a TAF indicates the probability of the occurence of specified weather phenomena.

• There is a two type of PROB; 1. PROB30 indicates a low probability of a change occurring.2. PROB40 indicates a high probability of a change occurring. • The code PROB can be followed by a time group of its own, and/or by an indicator, such as BECMG or

TEMPO.• The example of TAF below tells us that there is a high probability that, between 1000 UTC and 1400

UTC, there will be thunderstorms with heavy rain and hail, and from 3 to 4 oktas of cumulonimbus clouds at 500 feet.

TAF LTBA 130600Z 1307/1316 31015KT 8000 –SHRA SCT010 BKN018 PROB40 TEMPO 1014 +TSRAGR SCT005CB=

End of Message• An equals sign (=) appears at the end of the TAF reports to denote taht the message is complete.

TAF LTBA 100440Z 1006/1112 04009KT CAVOK

TEMPO 1006/1010 SCT030

PROB30 1101/1105 4000 BR SCT010

BECMG 1105/1108 SCT030 BKN100=

Bibliography• Oxford Aviation Academy PPL Meteorology, Book 4

• https://en.wikipedia.org/wiki/Terminal_aerodrome_forecast

• http://www.aviationweather.gov/adds/tafs

• https://www.aviationweather.gov/static/help/taf-decode.php

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Aviation Meteorology - Terminal Aerodrome Forecasts