A METAR is an observation: the weather at an airport at a given time, usually issued every 30 or 60 minutes. A TAF is a forecast for the airport, normally covering 24 or 30 hours. Both use the same building blocks.
A METAR, group by group
EGLL 100650Z 24018G32KT 2000 R27L/0550V0900U +TSRA BR FEW006 BKN012CB 09/07 Q0998 TEMPO 4000 RA
| Group | Meaning |
|---|---|
EGLL |
Station: London Heathrow |
100650Z |
10th of the month, 06:50 UTC |
24018G32KT |
Wind from 240° true at 18 kt, gusting 32 kt |
2000 |
Visibility 2,000 m (9999 means 10 km or more) |
R27L/0550V0900U |
Runway visual range on 27L, 550 to 900 m, increasing |
+TSRA |
Heavy thunderstorm with rain |
BR |
Mist |
FEW006 |
Few clouds at 600 ft above the airport |
BKN012CB |
Broken cumulonimbus at 1,200 ft |
09/07 |
Temperature 9 °C, dew point 7 °C (M means minus) |
Q0998 |
QNH 998 hPa (A2992 would be 29.92 inHg) |
TEMPO 4000 RA |
Trend: temporarily 4,000 m in rain |
Cloud amounts are in eighths of the sky (oktas): FEW 1–2, SCT scattered 3–4, BKN broken 5–7, OVC overcast 8. The ceiling is the lowest broken or overcast layer.
CAVOK (ceiling and visibility OK) replaces visibility, weather and cloud when visibility is 10 km or more, there is no cloud below 5,000 ft or the minimum sector altitude (whichever is higher), no cumulonimbus or towering cumulus, and no significant weather.
Weather codes
Codes combine an intensity, a descriptor and a phenomenon: -SHRA is light showers of rain, FZFG is freezing fog, VCTS is a thunderstorm in the vicinity.
| Intensity | Descriptor | Precipitation | Obscuration |
|---|---|---|---|
- light, + heavy, VC vicinity |
SH showers, TS thunderstorm, FZ freezing, BL blowing, DR drifting |
RA rain, DZ drizzle, SN snow, GR hail, PL ice pellets |
BR mist, FG fog, HZ haze, DU dust, SA sand, FU smoke |
Flight categories
Many briefing tools colour airports by flight category, using the US definitions:
| Category | Ceiling | Visibility | |
|---|---|---|---|
| VFR | above 3,000 ft | and | more than 5 SM |
| MVFR (marginal VFR) | 1,000 to 3,000 ft | or | 3 to 5 SM |
| IFR | 500 to below 1,000 ft | or | 1 to below 3 SM |
| LIFR (low IFR) | below 500 ft | or | below 1 SM |
Reading a TAF
TAF EGLL 100500Z 1006/1112 24015G25KT 9999 BKN020
TEMPO 1006/1010 4000 RA BKN010
PROB30 TEMPO 1012/1016 TSRA BKN014CB
BECMG 1018/1021 30010KT
The first line is the base forecast, valid from 06Z on the 10th to 12Z on the 11th. Then come the change groups:
- FM (from): a complete change at a set time, for example
FM110300. - BECMG (becoming): a gradual change during the period given.
- TEMPO (temporarily): fluctuations lasting less than an hour each, and less than half the period in total.
- PROB30 / PROB40: a 30 or 40 percent chance, on its own or with TEMPO.
When you plan, use the worst conditions forecast for the hour either side of your arrival time. The METAR and TAF decoder reads any report in plain English.
For flight simulation and training only. Real-world procedures vary by country and operator; always follow the published charts and your local rules.
Keep reading
- Altimetry, QNH and transition levels: What QNH, QFE and standard pressure mean, and when to change the altimeter setting.