Free METAR and TAF Decoder

What a METAR is

A METAR is a routine aviation weather report for an airport, issued about once an hour. It compresses the current wind, visibility, present weather, cloud layers, temperature, dewpoint, and altimeter setting into a single coded line. The format is standardized — it is defined for U.S. aviation in FAA Advisory Circular 00-45 (Aviation Weather Services) and follows the international ICAO and WMO conventions — so once you can read one METAR you can read them anywhere in the world. The trade-off is that the coding is dense, and that is exactly what the decoder above unpacks.

How to read a METAR, group by group

A METAR is read left to right in a fixed order. Take this observation as a worked example:

1. KJFK — the ICAO station identifier (New York's John F. Kennedy International).
2. 121651Z — the report time: the 12th day of the month at 16:51 Zulu (UTC). Aviation weather always uses Zulu time.
3. 18012G22KT — wind from 180 degrees true at 12 knots, gusting to 22 knots.
4. 10SM — visibility of 10 statute miles.
5. FEW045 SCT250 — few clouds at 4,500 feet and scattered clouds at 25,000 feet above the field. Cloud heights are given in hundreds of feet.
6. 28/17 — temperature 28 °C, dewpoint 17 °C. An M prefix means a negative value, so M05 is minus 5 °C.
7. A2992 — altimeter setting 29.92 inHg. Outside the U.S. this appears as a Q group in hectopascals, such as Q1013.
8. RMK AO2 SLP132 T02830172 — remarks: an automated station with a precipitation sensor, sea-level pressure 1013.2 hPa, and the precise temperature and dewpoint (28.3 °C / 17.2 °C).

Present weather: intensity, descriptor, phenomenon

Present-weather groups are built from an optional intensity, an optional descriptor, and one or more phenomena, concatenated together. Intensity is a leading - for light or + for heavy, with no sign meaning moderate and VC meaning in the vicinity. So -RA is light rain, +TSRA is a thunderstorm with heavy rain, FZFG is freezing fog, BLSN is blowing snow, and VCSH is showers in the vicinity. The decoder expands each combination for you.

METAR abbreviation reference

The most common codes you will meet in a METAR, grouped by what they describe:

How to read a TAF

A TAF (Terminal Aerodrome Forecast) uses the same wind, visibility, weather, and cloud coding as a METAR, but it forecasts conditions over a period — typically 24 to 30 hours — rather than reporting them now. After the station, issue time, and valid period, a TAF is a base forecast followed by change groups:

• FM (from) — a rapid, permanent change at the stated time; everything after it replaces the previous conditions. FM122000 means from the 12th at 20:00Z.
• BECMG (becoming) — a gradual change expected to occur within the stated window.
• TEMPO (temporary) — temporary fluctuations expected to last less than an hour each within the window.
• PROB30 / PROB40 — a 30% or 40% probability of the stated conditions occurring in the window.

Switch the decoder above to TAF mode and it separates the base forecast from each change group, decoding the period and conditions for every one.

Why times are always in Zulu

Every time in a METAR or TAF is in Zulu (UTC), so dispatch, the cockpit, and the controller all work from one clock regardless of local time zone. The report time 121651Z is the 12th at 16:51Z. If you need to convert that to or from your local time, the Zulu time converter handles the offset and daylight saving for any zone.