Aerodrome Weather Forecasts (TAF)
Have you ever wanted to predict the future, a weather predictor? Well, by using a TAF, you can do precisely that!
Historically, the acronym "TAF" stood for "Terminal Area Forecast", but this was changed to "Aerodrome Forecast" to avoid confusion with Area Forecasts. The "T" no longer means anything since using the word "Aerodrome" makes "Terminal" redundant. Still, we can't help ourselves - we commonly take it to mean "Terminal" Aerodrome Forecast, as do many publications. They are issued in the standard code format for forecasts issued for airports.
This tutorial will cover the two types of TAFs in use within New Zealand and how to decode them.
A TAF is an aerodrome forecast provided for a specific aerodrome presented in code.
A TREND is a forecast, valid for two hours following issue, attached to the end of a METAR, stating any significant changes from those described. While the TREND is valid, it supersedes the aerodrome TAF.
TAF - Domestic
Domestic TAFs are aerodrome forecasts provided for specific aerodromes and presented in the TAF code. They differ from International TAFs in that visibilities above 10km are included, as are cloud groups above 1500 ft. Winds at 2000 ft AGL and forecast QNH at the aerodrome are sometimes added at the end of the TAF.
The QNH forecast is for the maximum and minimum QNH values expected during the validity period of the TAF or during a specified validity period. The forecast is provided as a guide to the pressure range expected during a TAF or specified validity period. The primary purpose is to check the actual QNH passed to an aircraft to ensure that any transmission errors do not result in an incorrect altimeter setting. The QNH forecasts, appended to Domestic TAF, are NOT used for altimeter settings.
A forecast 2,000 ft wind is included to assist in determining the possibility of wind shear between 2,000 ft and the ground level.
Domestic TAFs are for preflight and inflight use and are available from the listed sites (below). However, apart from IFIS, a real-world pilots licence or Aero Club logon must be used.
Example - Domestic TAF
TAF NZRO 192313Z 2000/2012 01015G28KT 30KM -SHRA SCT020 BKN035 TEMPO 2001/2004 5000 +TSRAGS BKN010CB 2000FT WIND 36020KT QNH MNM 1015 MAX 1024
Decode of a Domestic TAF
TAF NZRO 192313Z 2000/2012
Aerodrome forecast for Rotorua, issued at 2313 UTC on the 19th of the month, valid from 0000 UTC to 1200 UTC on the 20th of the month
Surface wind: 010 degrees true, 15 knots gusts 28 knots
Visibility: 30 kilometres
Weather: Light shower of rain
Cloud: scattered cloud (3-4 oktas) with a base at 2000 feet above aerodrome level, broken cloud (5-7 oktas) with a base at 3500 feet above aerodrome level
TEMPO 2001/2004 5000 +TSRAGS
Temporarily, between 0100 and 0400 UTC on the 20th of the month, visibility will reduce to 5000 metres in heavy thunderstorms with rain and hail, and broken cumulonimbus cloud at 1000 feet above aerodrome level
2000FT WIND 36020KT
Forecast wind at 2000 feet 360 degrees true at 20 knots
QNH MNM 1015 MAX 1024
During the forecast period, the minimum and maximum QNH is expected to be 1015 hPa and 1024 hPa, respectively.
TAF - International
International TAFs are aerodrome forecasts provided for specific aerodromes and presented in the Terminal Aerodrome Forecast (TAF) code. They differ from Domestic TAFs in that they are in Annex 3 format where visibilities at or above 10 km and non-significant cloud groups are not included. Winds at 2000ft and forecast QNH are also not included.
International TAFs are only issued for NZAA, NZWN & NZCH.
International TAFs are for preflight and inflight use and are available from the listed sites (below). However, apart from IFIS, a real-world pilots licence or Aero Club logon must be used.
Example of an International TAF
TAF NZCH 102305Z 1100/1200 20008KT 9999 FEW012 SCT017 TEMPO 1100/1108 BKN012 BECMG 1108/1110 06010KT TEMPO 1108/1121 6000DZ BKN012
Decode of International TAF
|TAF NZCH 102305Z 1100/1200||Aerodrome forecast for Christchurch International Airport, issued at 2305 UTC on the 10th of the month, valid from 0000 UTC on the 11th of the month to 0000 UTC on the 12th of the month|
|20008KT||Surface wind: 200 degrees true, 8 knots|
|9999||Visibility: 10 kilometres or more|
|FEW012 SCT017||Cloud: few clouds (1-2 oktas) with a base at 1200 feet above aerodrome level, scattered clouds (3-4 oktas) with a base at 1700 feet above aerodrome level|
|TEMPO 1100/1108 BKN012||Temporarily, between 0000 and 0800 UTC on the 11th, broken cloud (5-7 oktas) with a base of 1200 feet above aerodrome level|
|BECMG 1108/1110 06010KT||Becoming, between 0800 and 1000 UTC on the 11th, wind 060 degrees true, 10 knots|
|TEMPO 1108/1121 6000DZ BKN012||Temporarily, between 0800 and 2100 UTC on the 11th, visibility will reduce to 6000 metres in drizzle, with broken cloud (5-7 oktas) at 1200 feet above aerodrome level|
Adapted from 'Aviation weather products', CAA