Terminal Aerodrome Forecasts (TAFS) — Page 492, Lesson 466

I want to walk you through Terminal Aerodrome Forecasts — TAFs. These are the aviation weather forecasts for airports, and they follow a very specific coded format that you need to read and interpret exactly. Let's start with the validity period. In the example we have: TAF EGTK 130600Z 1307/1316. The first part, 130600Z, tells us the date and time the forecast was issued — that's the 13th of the month at 0600 UTC. Then comes the validity period: 1307/1316. That means the forecast is valid from the 13th at 0700 UTC until 1600 UTC on the same day. So this is a nine-hour TAF — the period from 0700 to 1600 is nine hours. Now the wind group. The wind codes in a TAF are exactly the same as in a METAR. In our example: 31015KT. That means the mean wind direction is 310 degrees — and this is referenced to True north, not magnetic — at a wind speed of 15 knots. Next is the weather group. Again, the weather coding is identical to METAR. Our example shows 8000 –SHRA. The visibility is 8000 metres, and –SHRA means light showers of rain. The minus sign indicates light intensity. Now cloud — and here's where TAFs can be slightly different from METARs. In a TAF, if there is no cloud below the greater of 5000 feet or the minimum sector altitude, and if there is no CB — cumulonimbus — or TCU — towering cumulus — and CAVOK is not appropriate, then the code NSC is used. NSC stands for 'no significant cloud'. Also, just like in METARs, only CB or TCU clouds will be included in TAFs — other cloud types are not reported. In our example TAF, the cloud group is SCT010 BKN018. SCT means scattered, which is 3 to 4 oktas of cloud cover, at 1000 feet. BKN means broken, which is 5 to 7 oktas, at 1800 feet. So we're forecasting scattered cloud at 1000 feet and broken cloud at 1800 feet. Now, the main TAF information ends with the cloud group. This is important: TAFs do not contain temperature and dew point, QNH, recent weather, windshear, or runway state information. However, some countries do forecast maximum and minimum temperatures for the forecast period — but that's an addition, not standard. Only significant changes of weather follow the cloud group. These significant changes are introduced by codes called forecast change indicators. There are four distinctive TAF codes that indicate a change is expected in some or all of the forecast meteorological conditions. The nature of the change can vary — it may be rapid, gradual, or temporary. The codes are: FM, which means FROM; BECMG, which means BECOMING; TEMPO, which means TEMPORARILY; and PROB, which means PROBABILITY. These indicators tell you when and how conditions are expected to change during the forecast period.