TAFs & Metars

Definitions

• TAF - Terminal Aerodrome Forecast. A forecast given by an individual airfield. The duration of these forecasts are often for a 9 hours period but can be anything from 3 to 24 hours. The 24 hour forecasts are known as Long TAFs. The valid period is in the first bit of code eg. 121807Z. this means issued on the 12th at 1800hrs until 13th at 0700hrs.
• Metar - Meteorological Aerodrome Report. A report of the actual conditions at a particular airfield.

Below is a typical TAF display that is readily available from the Met Office. Once logged in, you just need to navigate to the TAF & Metar bulletins section. They’re free, but you’ll need to register to gain access to the more specialist areas. You can register here.

Without the knowledge to decode this information, TAFs make no sense at all and may as well be written in Martian. But once you understand how to break them down and what each section means, they become a very quick way to convey a forecast and in the case of Metars, it’s a quick way of knowing what’s going on!
Below is all you need to decode them;

TAF Format
[Station ID] [Origin Date/Time] [Valid Period] [Wind] [Horizontal Visibility] [Significant weather] [Cloud cover] [Significant changes]

To make things slightly more complicated, not all sections are present in all forecasts. Some airfields omit sections if there’s nothing worth saying, some can’t even be bothered to issue a TAF! But within this document there is sufficient info to decipher most TAFs easily. Failing that the Met office run courses for the really keen.

Each of the TAF sections are explained in more detail below.
 
Station ID
These four characters identify the air facility. EG means it’s in the UK

Origin Date/Time
The date and time when the forecast was completed. The first two digits are the day of the month, followed by the time (in UTC). For example, an origin date/ time of 171155Z means that the TAF was completed on the 17th at 1155 UTC.

Valid Period
The time period which the TAF covers, usually 24 hours. This consists of a two- digit date followed by a two-digit hour for the start period, then a two-digit ending date and two digit ending hour, e.g. 1306/1406 (0600 on 13th to 0600 on 14th). In the case of an amended forecast, or a forecast which is corrected or delayed, the valid period may be less than 24 hours.

Wind
The first three digits are the direction, in degrees from magnetic north, from which the wind will be blowing. The next two digits are the wind speed. Next is KT, the abbreviation for knots. If the wind is gusting, the abbreviation G is present followed by the maximum wind speed of the gusts. The BGA recommend a maximum gust factor of 10knots for any training by Basic Instructors. Here are some typical wind entries:
00000KT……. No wind/ calm
23012KT……. Wind direction 230 degrees. Wind speed 12 knots
33015G25KT...Wind direction 330 degrees. Wind speed 15 knots with gusts to 25 knots 
VRB03KT……Variable Wind Direction. Wind speed 3 knots.
    
Horizontal Visibility
This is a measure of how far features can be seen along the ground. These are measured in Kilometres.
9999 = 10 km or more; 0000 = less than 50 metres; 8000 = 8 kilometres.
  
Cloud cover
This is the amount of cloud cover (SKC, FEW, SCT, BKN, or OVC) followed by the height of the clouds given in thousands and hundreds of feet. For example,
SCT005 BKN025CB BKN250 means scattered clouds at 500 feet, broken cumulonimbus clouds at 2,500 feet, and broken clouds at 25,000 feet.
Cumulonimbus clouds the only cloud types predicted in TAFs. When the sky is obscured by fog or mist, a VV (vertical visibility) is used followed by the vertical visibility in hundreds of feet.

Cloud height is given in feet above airfield height.

Now that’s all explained, let’s look at one airfield’s TAF more closely.

TAF Abbreviations and Symbols

A full list of abbreviations used with TAFs can be found on the Met Office web site. Below is a list of the more common ones.