METAR and SPECI

A METAR is the routine aviation weather report for an aerodrome: a coded snapshot of the wind, visibility, weather, cloud, temperature and pressure observed at a stated time. A special meteorological report (SPECI) has exactly the same format and is issued between routine reports when conditions change significantly. With the TAF, the aerodrome forecast, the METAR / TAF pair is the core of every pre-flight briefing: the METAR says what is happening, the TAF what is expected (see TAF and trend forecasts).

The code is defined internationally by ICAO Annex 3 and the WMO Manual on Codes, as code forms FM 15 (METAR) and FM 16 (SPECI), and applied in the EU through Part-MET of Regulation (EU) 2017/373. The United States uses the same structure with its own units and a long remarks section, set out in the Federal Meteorological Handbook No. 1 (FMH-1) and the FAA Aviation Weather Handbook.

What METAR and SPECI are

A METAR is an observation, not a forecast. ICAO requires one every hour, or every half hour where regional agreement says so, as at many European aerodromes. US stations report hourly, shortly before the hour. A SPECI begins with the word SPECI instead of METAR and is issued whenever one of the criteria described below is met, for deterioration and improvement alike.

Many European METARs from larger aerodromes end with a TREND, a landing forecast valid for two hours using BECMG, TEMPO or NOSIG (no significant change). US METARs carry no trend.

Report layout and the date-time group

The groups always come in the same order, and a missing group is simply left out:

The wind is the mean over the previous 10 minutes. A gust (G) is added only when it exceeds the mean by 10 kt or more, and two extreme directions separated by V appear when the direction varies by 60° or more. VRB means no mean direction can be given, and 00000KT is calm.

Visibility is in metres: 9999 means 10 km or more and 0000 less than 50 m. RVR groups follow when the visibility or the RVR is below 1,500 m. P and M mean above and below the measurable range, and U, D or N gives the tendency: up, down or no change (see visibility and RVR).

Cloud amount is given in oktas: FEW 1 to 2, SCT 3 to 4, BKN 5 to 7 and OVC 8. Cloud height is in hundreds of feet above aerodrome level, and CB and TCU are the only cloud types ever named. VV gives the vertical visibility when fog, snow or other obscuration hides the sky. CAVOK replaces visibility, RVR, weather and cloud when all four of its conditions hold: visibility 10 km or more; no cloud below 5,000 ft or the highest minimum sector altitude, whichever is greater; no CB or TCU; and no significant weather. NSC means no significant cloud when CAVOK does not apply, and NCD means an automatic station detected no cloud.

Temperatures are whole degrees Celsius, with M for minus. QNH is rounded down to the whole hectopascal (see altimeter settings).

The main differences in US reports:

View full schematic

Present weather codes and descriptors

The weather (WX) group uses the WMO present weather codes, which are the same in METAR, SPECI and TAF. Each group is built from an intensity sign, an optional descriptor and one or more phenomena. The sign is − for light, none for moderate and + for heavy, and it applies to precipitation. When several types fall together the dominant one comes first, as in -RASN.

Under ICAO rules FG is reported when fog reduces visibility below 1,000 m, and BR when visibility is 1,000 to 5,000 m. Shallow, patchy or partial fog (MIFG, BCFG, PRFG) can be reported with higher visibility. DR describes snow, dust or sand carried along close to the ground, BL the same raised to eye level or above.

Recent weather and vicinity

Recent weather (RE) reports operationally significant weather seen since the previous routine report or during the last hour, whichever is shorter, that has stopped by the time of the observation. RETS is a recent thunderstorm, RERA recent rain, REFZRA recent freezing rain. RE groups belong to reports only, never to a TAF. US reports give the same information as start and end times in the remarks instead.

Vicinity (VC) marks weather happening now close to the aerodrome, but not at it. ICAO defines the vicinity as roughly 8 to 16 km from the aerodrome reference point, and allows VC only with TS, DS, SS, FG, FC, SH, PO, BLDU, BLSA, BLSN and VA. VCSH is showers in the vicinity, VCTS a thunderstorm in the vicinity. In the United States VC covers 5 to 10 statute miles from the observing point.

In ICAO reports, windshear reported along the take-off or approach path is added as supplementary information: WS followed by the runway, for example WS R27 (see windshear and microbursts).

Runway state group and SNOCLO

For many years winter METARs in Europe ended with a runway state group: R and the runway designator, a slash, then six figures. The first gives the type of deposit (0 clear and dry up to 9 frozen ruts or ridges). The second gives its extent (1, 2, 5 or 9, for up to 10 %, 11 to 25 %, 26 to 50 % and 51 to 100 % of the runway). The next two give the depth, and the last two the friction coefficient or braking action. R88 meant all runways, and R99 repeated the previous report because no new information was available. CLRD meant the contamination had been cleared. SNOCLO, which exam material often spells SNOWCLO (aerodrome closed due to snow), replaced the whole group when snow closed the aerodrome.

With the Global Reporting Format for runway surface conditions, the group was dropped from the ICAO METAR: in the EU from 12 August 2021 and worldwide from 4 November 2021. Runway condition now reaches pilots through the runway condition report and SNOWTAM (see wet and contaminated runways). Some states still append the old group, and exam question banks still ask about it.

The remarks (RMK) section

METAR remarks (RMK) follow the body of the report. ICAO leaves remarks to national practice and most European civil reports carry none, but in the United States they are routine:

• AO1 or AO2: the type of automated station.
• PK WND 28035/1745: peak wind 280° at 35 kt at 1745 UTC.
• WSHFT 1730 FROPA: wind shift at 1730, caused by a frontal passage.
• TSB2058E2140, RAB15E40: thunderstorm or rain began and ended at the times given.
• PRESFR or PRESRR: pressure falling or rising rapidly, at 0.06 inHg per hour or more.
• SLP132: sea-level pressure 1013.2 hPa, with the leading 9 or 10 omitted.
• P0010: 0.10 in of precipitation in the past hour.
• T01170094: temperature 11.7 °C and dew point 9.4 °C, in tenths; a leading 1 instead of 0 means minus.
• $: the automated station needs maintenance.

Automated reports: AUTO, ASOS and AWOS

An AUTO METAR is produced entirely by an automated weather station (AUTO, AO1/AO2) with no human check, and the word AUTO follows the date-time group. Such reports are common at aerodromes outside their staffed hours and at smaller fields with no observer. Elements the sensors cannot determine are replaced by slashes, and the codes NCD and UP exist for this purpose. The cloud picture comes from a ceilometer that looks straight up and sees only what drifts over it.

In the United States most observations come from automated stations. The Automated Surface Observing System (ASOS) is the national network, run jointly by the National Weather Service, the FAA and the Department of Defense. The Automated Weather Observing System (AWOS) comes in levels from AWOS-A, which reports only an altimeter setting, to AWOS-III P/T with present weather and thunderstorm detection. The automated station type (AO1 / AO2) in the remarks shows the equipment. AO1 has no precipitation discriminator. An automated station with precipitation discriminator (AO2) can tell rain from snow. An automated CLR means no cloud was detected below 12,000 ft, not that the sky is clear.

When a SPECI is issued

SPECI criteria differ between the ICAO system and the United States:

Two decoded examples

A European report in low visibility:

METAR LFPG 120530Z 21008KT 1200 R27L/1100U R26R/1400N BR BKN003 OVC008 09/08 Q1012 RERA BECMG 3000

A US report with a thunderstorm:

METAR KORD 221951Z 24012G22KT 2SM -TSRA BR BKN008 OVC020CB 22/20 A2985 RMK AO2 PK WND 25028/1932 TSB25 SLP107 P0012 T02170200

Library articles are written for study and exam preparation. They do not replace your aircraft's approved documentation, your operator's procedures or the regulations themselves.