What is a weather report?
Before a flight, a pilot reads coded messages: the observation at an aerodrome, its forecast, the warnings along the route. ICAO calls them OPMET, operational meteorological information. Everywhere, they follow the same construction, set by ICAO and the WMO, with a few national variants — in the United States above all.
The reports at a glance
- METARThe routine observation at an aerodromeThe aerodrome's weather station · An aerodrome
- SPECIA special observation, when the weather changes markedlyThe aerodrome's weather station · An aerodrome
- TAFThe forecast for an aerodromeAn aerodrome meteorological office · An aerodrome
- SIGMETA phenomenon hazardous to en-route flightsA meteorological watch office · An FIR
- AIRMETA phenomenon hazardous to low-level flightsA meteorological watch office · An FIR or part of it
- GAMETThe area forecast for low-level flightsA designated meteorological office · An FIR or part of it
- VAA · TCA · SWXVolcanic ash, tropical cyclones, space weatherAdvisory centres · Wide regions
METARThe observation at an aerodrome
A METAR states the weather at an aerodrome at the time of observation: wind, visibility, present weather, cloud, temperature, pressure. The station issues it every 30 or 60 minutes — every half hour in France. A trend may close it: what is expected to change within the next two hours.
- Issued by
- The aerodrome's weather station
- Frequency
- Every 30 or 60 minutes
- Trend
- The next 2 hours
METAR EICK 021330Z 22021G32KT 3000 -RA BR SCT007 BKN008 15/14 Q1021 TEMPO 2000 RA
METAR — Message type
routine observation.
EICK — ICAO location indicator
Cork aerodrome, Ireland.
021330Z — Day and time
the 2nd of the month, at 13:30 UTC.
22021G32KT — Wind
from 220°, 21 kt, gusting to 32 kt.
3000 — Visibility
3000 m, the prevailing visibility.
-RA BR — Present weather
light rain, mist.
SCT007 BKN008 — Cloud
scattered (3 or 4 oktas) at 700 ft, broken (5 to 7 oktas) at 800 ft.
15/14 — Temperatures
15 °C, dew point 14 °C.
Q1021 — QNH
1021 hPa.
TEMPO 2000 RA — Trend
temporarily within the next two hours: 2000 m, moderate rain.
Depending on the weather, other groups take their place in the same order: runway visual range (R27L/0550N), vertical visibility when the sky is obscured (VV002), recent weather (RERA).
CAVOK alone replaces the visibility, present weather and cloud: visibility of 10 km or more, no cloud below 5000 ft, no cumulonimbus or towering cumulus, no significant weather.
In the United States
Visibility in statute miles (10SM), altimeter setting in inches of mercury (A2992), and often a long remarks section (RMK).
StandardsICAO Annex 3PANS-MET (Doc 10157)WMO-No. 306, FM 15FMH-1, in the United States
SPECIThe special observation
A SPECI has the form of a METAR, but it does not wait for the hour: the station issues it when the wind, the visibility, low cloud or present weather change beyond set thresholds. France no longer produces them; they are common in the United States, like this one.
SPECI KBKL 021237Z 36020G32KT 5SM -RA BR FEW007 OVC013 15/13 A3003 RMK AO2 PK WND 35032/1229 P0005 T01500133 $
SPECI — Message type
special observation.
KBKL — ICAO location indicator
Cleveland Burke Lakefront, United States.
021237Z — Day and time
the 2nd at 12:37 UTC, outside the routine schedule.
36020G32KT — Wind
from 360°, 20 kt, gusting to 32 kt.
5SM — Visibility
5 statute miles.
-RA BR — Present weather
light rain, mist.
FEW007 OVC013 — Cloud
few (1 or 2 oktas) at 700 ft, overcast at 1300 ft.
15/13 — Temperatures
15 °C, dew point 13 °C.
A3003 — Altimeter setting
30.03 inches of mercury.
RMK AO2 PK WND 35032/1229 P0005 T01500133 $ — Remarks
automated station that tells rain from snow; peak wind from 350° at 32 kt, at 12:29; 0.05 inch of precipitation in the past hour; temperatures to the tenth of a degree; maintenance needed.
StandardsICAO Annex 3PANS-MET (Doc 10157)WMO-No. 306, FM 16FMH-1, in the United States
TAFThe forecast for an aerodrome
A TAF forecasts the weather at an aerodrome for a period written in the message. Its first groups look like those of a METAR — wind, visibility, weather, cloud — but forecast; the changes come next. In France, a short TAF is valid for 9 hours and renewed every 3 hours; a long TAF is valid for 24 or 30 hours and renewed every 6 hours. TAF AMD marks an amended TAF.
- Issued by
- An aerodrome meteorological office
- Validity in France
- 9, 24 or 30 hours
- Renewal
- Every 3 or 6 hours
TAF EICK 021100Z 0212/0312 22018KT 9999 SCT008 BKN025 TEMPO 0212/0217 23020G33KT 4000 -RA BKN008 FEW020CB PROB40 TEMPO 0212/0217 2000 RA BR BKN004 BECMG 0216/0218 30007KT PROB30 TEMPO 0304/0309 0500 FG BKN001
TAF — Message type
aerodrome forecast.
EICK — ICAO location indicator
Cork.
021100Z — Issue
the 2nd at 11:00 UTC.
0212/0312 — Validity
from the 2nd at 12:00 to the 3rd at 12:00 UTC.
22018KT 9999 SCT008 BKN025 — Base forecast
wind from 220°, 18 kt; 10 km or more; scattered cloud at 800 ft, broken at 2500 ft.
TEMPO 0212/0217 23020G33KT 4000 -RA BKN008 FEW020CB — Temporarily
from 12:00 to 17:00: wind from 230°, 20 kt, gusting to 33 kt; 4000 m in light rain; broken cloud at 800 ft, a few cumulonimbus at 2000 ft.
PROB40 TEMPO 0212/0217 2000 RA BR BKN004 — 40 % probability
temporarily, from 12:00 to 17:00: 2000 m, rain and mist; broken cloud at 400 ft.
BECMG 0216/0218 30007KT — Becoming
between 16:00 and 18:00, the wind changes to 300°, 7 kt.
PROB30 TEMPO 0304/0309 0500 FG BKN001 — 30 % probability
on the 3rd, temporarily from 04:00 to 09:00: fog, 500 m; broken cloud at 100 ft.
The changes
- FM
- from a given time: the forecast that follows replaces the previous one.
- BECMG
- conditions change during the interval, then apply afterwards.
- TEMPO
- temporarily, during the interval.
- PROB30, PROB40
- with a probability of 30 or 40 %.
- TX, TN
- the forecast maximum and minimum temperatures, and their times.
StandardsICAO Annex 3PANS-MET (Doc 10157)WMO-No. 306, FM 51NWS 10-813, in the United States
SIGMETHazardous weather en route
A SIGMET warns of a phenomenon that threatens the safety of en-route flights: thunderstorms, severe turbulence, severe icing, severe mountain waves, sandstorms or duststorms, volcanic ash, tropical cyclones, radioactive cloud. A meteorological watch office issues it for a flight information region (FIR), one SIGMET per phenomenon. It is valid for 4 hours at most; 6 hours for volcanic ash and tropical cyclones.
- Issued by
- A meteorological watch office
- Covers
- An FIR
- Validity
- 4 hours at most, 6 for ash and cyclones
EBBU SIGMET U01 VALID 202000/210000 EBBR- EBBU BRUSSELS FIR SEV TURB FCST WI N5107 E00357 - N5105 E00500 - N5015 E00535 - N5040 E00333 - N5107 E00357 SFC/FL120 STNR WKN=
EBBU — Region
the Brussels FIR.
SIGMET U01 — Number
first SIGMET of the day for turbulence (U).
VALID 202000/210000 — Validity
the 20th, from 20:00 to midnight UTC.
EBBR- — Originator
the Brussels meteorological watch office.
EBBU BRUSSELS FIR — Region
the FIR, in full.
SEV TURB — Phenomenon
severe turbulence.
FCST — Observed or forecast
forecast (OBS: observed).
WI N5107 E00357 - N5105 E00500 - N5015 E00535 - N5040 E00333 - N5107 E00357 — Where
within the polygon formed by these points.
SFC/FL120 — Levels
from the surface to flight level 120.
STNR — Movement
stationary (MOV: moving).
WKN= — Change
weakening (INTSF: intensifying; NC: no change). The = sign closes the message.
The letter of the number
In the States that apply Regulation (EU) 2017/373, the number of a SIGMET starts with a letter that names the phenomenon, followed by two digits; the count restarts every day at 00:01 UTC.
- TThunderstorms
- UTurbulence
- IIcing
- FFreezing precipitation
- MMountain waves
- DDuststorm
- SSandstorm
- RRadioactive cloud
- AVolcanic ash
- CTropical cyclone
Three families
The transmission heading tells apart WS for en-route phenomena, WV for volcanic ash and WC for tropical cyclones. The United States adds domestic SIGMETs, including convective SIGMETs.
StandardsICAO Annex 3PANS-MET (Doc 10157)EUR Doc 014NWS 10-811, in the United States
AIRMETLow-level flights
An AIRMET has the form of a SIGMET, for less severe phenomena that threaten flights below FL100 — FL150 in mountainous areas — and that the forecasts issued for those flights do not contain: isolated thunderstorms, moderate turbulence or icing, for example. France issues none: these phenomena and their thresholds are taken into account in the TEMSI chart.
EHAA AIRMET 01 VALID 070015/070300 EHDB- EHAA AMSTERDAM FIR ISOL TS OBS WI N52 E003 - N52 E004 - N51 E004 - N51 E003 TOP FL330 MOV E WKN=
EHAA — Region
the Amsterdam FIR.
AIRMET 01 — Number
first AIRMET of the day.
VALID 070015/070300 — Validity
the 7th, from 00:15 to 03:00 UTC.
EHDB- — Originator
the De Bilt meteorological watch office.
EHAA AMSTERDAM FIR — Region
the FIR, in full.
ISOL TS — Phenomenon
isolated thunderstorms.
OBS — Observed or forecast
observed.
WI N52 E003 - N52 E004 - N51 E004 - N51 E003 — Where
within this quadrilateral.
TOP FL330 — Levels
tops at flight level 330.
MOV E — Movement
towards the east.
WKN= — Change
weakening.
StandardsICAO Annex 3PANS-MET (Doc 10157)EUR Doc 014
The site's decoder does not read AIRMETs.
GAMETThe area forecast
A GAMET is an area forecast in abbreviated plain language for low-level flights, over an FIR or part of it, prepared by the meteorological office that the meteorological authority designates. An AIRMET reports only what it does not already say.
StandardsICAO Annex 3PANS-MET (Doc 10157)EUR Doc 014
The site's decoder does not read GAMETs.
VAA · TCA · SWXThe advisory centres
Three families of messages come neither from an aerodrome nor from an FIR, but from advisory centres: volcanic ash advisories (VAA), issued by the VAACs; tropical cyclone advisories (TCA), issued by the TCACs; space weather advisories (SWX), on solar activity and its effects on HF communications, satellite navigation and radiation at altitude. SIGMETs for ash and cyclones rely on the first two.
StandardsICAO Annex 3PANS-MET (Doc 10157)
TAC · IWXXMTwo ways of writing the same message
The pilot reads the traditional alphanumeric code (TAC): that is what this page shows. Between systems, the same messages also travel as IWXXM, an XML format defined by ICAO and the WMO — METAR, SPECI, TAF, SIGMET, AIRMET, and the ash, cyclone and space weather advisories. The content does not change; only the writing does.
Sources
ICAO texts are sold; those of the WMO, ICAO Europe, the European Union and national services are free.
- ICAOAnnex 3 — Meteorological Service for International Air NavigationPaid · store.icao.int
21st edition (Amendment 82), applicable since 27 November 2025. The elements each message contains.
- ICAOPANS-MET — Procedures for Air Navigation Services, Meteorology (Doc 10157)Paid · store.icao.int
1st edition, applicable since 27 November 2025. The message templates: METAR and SPECI, TAF, SIGMET, AIRMET.
- ICAOManual of Aeronautical Meteorological Practice (Doc 8896)Paid · store.icao.int
The practical guide for aeronautical meteorological services, with examples.
- WMOManual on Codes, Volume I.1, Part A (WMO-No. 306)Free · library.wmo.int
2019 edition, frozen. The code group by group: FM 15 METAR, FM 16 SPECI, FM 51 TAF.
- ICAO EuropeEUR Doc 014 — EUR SIGMET and AIRMET GuideFree · icao.int
5th edition, 2023, revised December 2023. European SIGMETs and AIRMETs, with official examples — including those on this page.
- European UnionImplementing Regulation (EU) 2017/373, Annex V (Part-MET)Free · eur-lex.europa.eu
Who issues what in Europe, and what meteorological services must provide.
- Météo-FranceGuide aviation, 2024 editionFree · aviation.meteo.fr
The decoding sheets for METARs, TAFs and SIGMETs, and French practice.
- United StatesFMH-1 — Federal Meteorological Handbook No. 1Free · icams-portal.gov
US METARs and SPECIs: miles, inches of mercury, remarks.
- United StatesNWS Instructions 10-813 (TAF) and 10-811 (SIGMET)Free · weather.gov
US TAFs and SIGMETs, including convective SIGMETs.
- ICAOManual on the ICAO Meteorological Information Exchange Model (Doc 10003)Paid · store.icao.int
The IWXXM format, described for those who exchange it.
- WMOIWXXM — Manual on Codes, Volume I.3 (WMO-No. 306)Free · community.wmo.int
The normative definition of the format, its schemas and their versions.