What is a METAR?
A METAR (METeorological Aerodrome Report) is a routine weather observation at an airport. Most airports issue one every 30 or 60 minutes, and an extra report, a SPECI, when the weather changes significantly in between. A METAR describes the weather as it was observed at that moment; it is not a forecast.
A METAR, group by group
Here's a METAR for Amsterdam Schiphol:
| Group | Meaning |
|---|---|
| EHAM | ICAO code of the airport: Amsterdam Schiphol. |
| 131725Z | Observed on day 13 of the month at 17:25 UTC (Z = Zulu time). |
| 24012G22KT | Wind from 240° (true north) at 12 knots, gusting 22 knots. VRB03KT means variable direction at 3 knots, 00000KT means calm. |
| 210V270 | The wind direction varies between 210° and 270°. |
| 9999 | Visibility 10 km or more. Otherwise in metres: 4000 is 4 km, 0800 is 800 m. |
| -SHRA | Light (-) rain showers (SH + RA). See weather codes. |
| FEW030 | A few clouds (1–2 oktas) with the base at 3,000 ft above the airport. |
| SCT045 | Scattered clouds (3–4 oktas) at 4,500 ft. |
| 14/08 | Temperature 14 °C, dewpoint 8 °C. Below zero gets an M: M02/M05. |
| Q1018 | QNH 1018 hPa: set this on the altimeter to read altitude above mean sea level. |
| NOSIG | No significant change expected in the next two hours (a trend forecast). |
Two more groups you'll see often. CAVOK (Ceiling And Visibility OK) replaces visibility, weather and clouds when visibility is 10 km or more, there's no cloud below 5,000 ft (or the highest minimum sector altitude, if higher), no cumulonimbus or towering cumulus, and no significant weather. R27/0600 is a runway visual range: 600 m along runway 27. Anything after RMK is a remark in local format.
The temperature–dewpoint spread is worth a look: when the two are close together, as in 09/08, fog or low cloud can form quickly, especially in the evening.
Clouds and ceiling
Cloud groups give the amount in oktas (eighths of the sky) and the height of the base in hundreds of feet above the airport.
| Code | Meaning |
|---|---|
| FEW | Few: 1–2 oktas |
| SCT | Scattered: 3–4 oktas |
| BKN | Broken: 5–7 oktas |
| OVC | Overcast: 8 oktas |
| VV002 | Vertical visibility 200 ft: the sky is obscured, for example by fog |
| NSC / NCD | No significant cloud / no cloud detected (automatic station) |
| CB / TCU | Added to a group, as in SCT030CB: cumulonimbus or towering cumulus |
The ceiling is the base of the lowest layer that is broken or overcast, or the vertical visibility. In FEW008 BKN014 OVC030 the ceiling is 1,400 ft: the few clouds at 800 ft don't count.
Weather codes
Weather is written as an optional intensity, an optional descriptor and one or more phenomena. - is light, no sign is moderate, + is heavy, and VC means in the vicinity (within about 8 km, but not at the airport). So +TSRA is a thunderstorm with heavy rain, and FZFG is freezing fog.
| Code | Meaning |
|---|---|
| RA / DZ | Rain / drizzle |
| SN / SG / GR / GS | Snow / snow grains / hail / small hail |
| FG / BR / HZ | Fog (visibility under 1,000 m) / mist / haze |
| TS | Thunderstorm |
| SH | Showers, as in SHRA or SHSN |
| FZ | Freezing, as in FZRA or FZFG |
| BL / DR | Blowing / low drifting, as in BLSN |
| MI / BC | Shallow / patches, as in MIFG or BCFG |
| RE | Recent: the weather ended within the last hour, as in RETS |
What is a TAF?
A TAF (Terminal Aerodrome Forecast) is the forecast for the area within about 5 nautical miles of an airport. It usually covers 9 to 30 hours and is issued every 3 or 6 hours. It uses the same groups as a METAR, plus change groups that say when and how the weather is expected to change.
A TAF, group by group
| Group | Meaning |
|---|---|
| 131620Z | Issued on the 13th at 16:20 UTC. |
| 1318/1424 | Valid from the 13th at 18:00 UTC until the 14th at 24:00 UTC. |
| 24012KT 9999 FEW030 SCT045 | The base forecast: wind 240° at 12 knots, 10 km or more, a few clouds at 3,000 ft, scattered at 4,500 ft. |
| TEMPO 1321/1401 | Between 21:00 and 01:00 UTC, temporarily: visibility 6 km in light rain showers, scattered cloud at 3,000 ft. |
| BECMG 1405/1407 | Between 05:00 and 07:00 UTC the wind changes to 270° at 10 knots, and stays that way. |
| PROB30 TEMPO 1410/1414 | A 30% chance of temporary rain with 4 km visibility and a broken ceiling at 1,200 ft between 10:00 and 14:00 UTC. |
Only the groups that change are repeated. After the BECMG group, the forecast is 27010KT with the visibility and clouds of the base forecast.
BECMG, TEMPO, FM and PROB
- FM (from), as in
FM141300: from the 14th at 13:00 UTC the weather changes quickly, and everything after it replaces the forecast before. - BECMG (becoming): a lasting change that happens gradually or at some point during the period. After it, the new conditions apply.
- TEMPO (temporary): fluctuations that each last less than an hour and together less than half the period. In between, the base forecast applies.
- PROB30 / PROB40: a 30% or 40% probability of the conditions that follow, alone or combined with TEMPO.
A TEMPO or PROB group is easy to overlook in a long TAF, and it is often the one that matters for your flight. That's why the TAF timeline in AirportWX marks these periods separately.
VFR, MVFR, IFR and LIFR
Flight rules categories summarise ceiling and visibility in one word. AirportWX uses the FAA limits; the category is set by whichever of the two is worse.
| Category | Ceiling | Visibility |
|---|---|---|
| VFR | Above 3,000 ft | and more than 5 statute miles (8 km) |
| MVFR | 1,000 to 3,000 ft | or 3 to 5 statute miles |
| IFR | 500 to below 1,000 ft | or 1 to below 3 statute miles |
| LIFR | Below 500 ft | or below 1 statute mile (1.6 km) |
These categories are a quick summary, not legal minima. The VFR minima that apply to your flight depend on the airspace and your country's rules.
US reports
METARs from the United States and Canada differ in a few places. Visibility is in statute miles (10SM, 1/2SM), the altimeter setting is in inches of mercury (A2992 is 29.92 inHg), and the remarks section often contains extra data, such as SLP for sea-level pressure or T01390083 for the temperature and dewpoint in tenths of a degree.
Let the app do the decoding
AirportWX decodes every METAR and TAF for you, shows the TAF as a timeline and keeps the raw report one tap away, so you can check your reading against it. The app also contains a guide to every abbreviation, free for everyone.
