METAR

METAR is a format for reporting weather information. A METAR weather report is predominantly used by aircraft pilots, and by meteorologists, who use aggregated METAR information to assist in weather forecasting.

Raw METAR is the most common format in the world for the transmission of observational weather data. It is highly standardized through the International Civil Aviation Organization (ICAO), which allows it to be understood throughout most of the world.

Naming

The United States Federal Aviation Administration (FAA) lays down the definition in its publication the Aeronautical Information Manual as aviation routine weather report[1] while the international authority for the code form, the World Meteorological Organization (WMO), holds the definition to be aerodrome routine meteorological report. The National Oceanic and Atmospheric Administration (part of the United States Department of Commerce) and the United Kingdom's Met Office both employ the definition used by the FAA. METAR is also known as Meteorological Terminal Aviation Routine Weather Report[2] or Meteorological Aerodrome Report.[3]

Origin

METARs typically come from airports or permanent weather observation stations. Reports are generated once an hour or half-hour, but if conditions change significantly, a report known as a special (SPECI) may be issued. Some METARs are encoded by automated airport weather stations located at airports, military bases, and other sites. Some locations still use augmented observations, which are recorded by digital sensors, encoded via software, and then reviewed by certified weather observers or forecasters prior to being transmitted. Observations may also be taken by trained observers or forecasters who manually observe and encode their observations prior to transmission.

History

The METAR format was introduced 1 January 1968 internationally and has been modified a number of times since. North American countries continued to use a Surface Aviation Observation (SAO) for current weather conditions until 1 June 1996, when this report was replaced with an approved variant of the METAR agreed upon in a 1989 Geneva agreement. The WMO's publication No. 782 "Aerodrome Reports and Forecasts" contains the base METAR code as adopted by the WMO member countries.[4]

Information contained in a METAR

A typical METAR contains data for the temperature, dew point, wind direction and speed, precipitation, cloud cover and heights, visibility, and barometric pressure. A METAR may also contain information on precipitation amounts, lightning, and other information that would be of interest to pilots or meteorologists such as a pilot report or PIREP, colour states and runway visual range (RVR).

In addition, a short period forecast called a TREND may be added at the end of the METAR covering likely changes in weather conditions in the two hours following the observation. These are in the same format as a Terminal Aerodrome Forecast (TAF).

The complement to METARs, reporting forecast weather rather than current weather, are TAFs. METARs and TAFs are used in VOLMET broadcasts.

Regulation

METAR code is regulated by the World Meteorological Organization in consort with the International Civil Aviation Organization. In the United States, the code is given authority (with some U.S. national differences from the WMO/ICAO model) under the Federal Meteorological Handbook No. 1 (FMH-1), which paved the way for the U.S. Air Force Manual 15-111[5] on Surface Weather Observations, being the authoritative document for the U.S. Armed Forces. A very similar code form to the METAR is the SPECI. Both codes are defined at the technical regulation level in WMO Technical Regulation No. 49, Vol II, which is copied over to the WMO Manual No. 306 and to ICAO Annex III.

METAR conventions

Although the general format of METARs is a global standard, the specific fields used within that format vary somewhat between general international usage and usage within North America. Note that there may be minor differences between countries using the international codes as there are between those using the North American conventions. The two examples which follow illustrate the primary differences between the two METAR variations.[6][7]

Example METAR codes

International METAR codes

The following is an example METAR from Burgas Airport in Burgas, Bulgaria. It was taken on 4 February 2005 at 16:00 Coordinated Universal Time (UTC).

METAR LBBG 041600Z 12012MPS 090V150 1400 R04/P1500N R22/P1500U +SN BKN022 OVC050 M04/M07 Q1020 NOSIG 8849//91=

  • METAR indicates that the following is a standard hourly observation.
  • LBBG is the ICAO airport code for Burgas Airport.
  • 041600Z indicates the time of the observation. It is the day of the month (04) followed by the time of day (1600 Zulu time, which equals 4:00 pm Greenwich Mean Time or 6:00 pm local time).
  • 12012MPS indicates the wind direction is from 120° (east-southeast) at a speed of 12 m/s (23 knots; 27 mph; 44 km/h). Speed measurements can be in knots (abbreviated KT) or meters per second (abbreviated MPS).
  • 090V150 indicates the wind direction is varying from 90° true (east) to 150° true (south-southeast).
  • 1400 indicates the prevailing visibility is 1,400 m (4,600 ft).
  • R04/P1500N indicates the Runway Visual Range (RVR) along runway 04 is 1,500 m (4,900 ft) and not changing significantly.
  • R22/P1500U indicates RVR along runway 22 is 1,500 m (4,900 ft) and rising.
  • +SN indicates snow is falling at a heavy intensity. If any precipitation begins with a minus or plus (-/+), it's either light or heavy.
  • BKN022 indicates a broken (over half the sky) cloud layer with its base at 2,200 ft (670 m) above ground level (AGL). The lowest "BKN" or "OVC" layer specifies the cloud ceiling.
  • OVC050 indicates an unbroken cloud layer (overcast) with its base at 5,000 ft (1,500 m) above ground level (AGL).
  • M04/M07 indicates the temperature is −4 °C (25 °F) and the dew point is −7 °C (19 °F). An M in front of the number indicates that the temperature/dew point is below zero Celsius.
  • Q1020 indicates the current altimeter setting (in QNH) is 1,020 hPa (30.12 inHg).
  • NOSIG is an example of a TREND forecast which is appended to METARs at stations while a forecaster is on watch. NOSIG means that no significant change is expected to the reported conditions within the next 2 hours.
  • 8849//91 indicates the condition of the runway:
    • 88 indicates either a specific runway (e.g. 25 = Rwy 25 or 25L; adding 50 will indicate Right Runway) or all the airport's runways ("88").
    • 99 indicates repetition of the last message as no new information received.

Some locations will report the runway using 3 characters (e.g. 25L)

    • 4 means the runway is coated with dry snow
    • 9 means 51% to 100% of the runway is covered
    • // means the thickness of the coating was either not measurable or not affecting usage of the runway
    • 91 means the braking index is bad, in other words the tires have bad grip on the runway
  • CAVOK is an abbreviation for Ceiling And Visibility OK, indicating no cloud below 5,000 ft (1,500 m) or the highest minimum sector altitude and no cumulonimbus or towering cumulus at any level, a visibility of 10 km (6 mi) or more and no significant weather change.[8]
  • = indicates the end of the METAR

North American METAR codes

North American METARs deviate from the WMO (who write the code on behalf of ICAO) FM 15-XII code. Details are listed in the FAA's Aeronautical Information Manual (AIM), but the non-compliant elements are mostly based on the use of non-standard units of measurement. This METAR example is from Trenton-Mercer Airport near Trenton, New Jersey, and was taken on 5 December 2003 at 18:53 UTC.

METAR KTTN 051853Z 04011KT 1/2SM VCTS SN FZFG BKN003 OVC010 M02/M02 A3006 RMK AO2 TSB40 SLP176 P0002 T10171017=[9]

  • METAR indicates that the following is a standard hourly observation.
  • KTTN is the ICAO identifier for the Trenton-Mercer Airport.
  • 051853Z indicates the day of the month is the 5th and the time of day is 1853 Zulu/UTC, or 1:53PM Eastern Standard Time.
  • 04011KT indicates the wind is from 040° true (north east) at 11 knots (20 km/h; 13 mph). In the United States, the wind direction must have a 60° or greater variance for variable wind direction to be reported and the wind speed must be greater than 3 knots (5.6 km/h; 3.5 mph).
  • 1/2SM indicates the prevailing visibility is 12 mi (800 m) SM = statute mile.
  • VCTS indicates a thunderstorm (TS) in the vicinity (VC), which means from 5–10 mi (8–16 km).
  • SN indicates snow is falling at a moderate intensity; a preceding plus or minus sign (+/-) indicates heavy or light precipitation. Without a +/- sign, moderate precipitation is assumed.
  • FZFG indicates the presence of freezing fog.
  • BKN003 OVC010 indicates a broken (58 to 78 of the sky covered) cloud layer at 300 ft (91 m) above ground level (AGL) and an overcast (8/8 of the sky covered) layer at 1,000 ft (300 m).
  • M02/M02 indicates the temperature is −2 °C (28 °F) and the dew point is −2 °C (28 °F). An M in front of the number indicates a negative Celsius temperature/dew point ("minus").
  • A3006 indicates the altimeter setting is 30.06 inHg (1,018 hPa).
  • RMK indicates the remarks section follows.

Note that what follows are not part of standard observations outside of the United States and can vary significantly.

  • AO2 indicates that the station is automated with a precipitation discriminator (rain/snow) sensor.[10] Stations that aren't equipped with a rain/snow sensor are designated AO1.[11]
  • TSB40 indicates the thunderstorm began at 40 minutes past the hour at 1840 Zulu/UTC, or 1:40 p.m. Eastern Standard Time.
  • SLP176 indicates the current barometric pressure extrapolated to sea level is 1,017.6 hPa (30.05 inHg).
  • P0002 indicates that 0.02 inches (0.5 mm) of liquid-equivalent precipitation accumulated during the last hour.
  • T10171017 is a breakdown of the temperature and dew point in eight digits separated into two groups of four. The first four digits (1017) indicate the temperature. The first digit (1) designates above or below zero Celsius (0=above zero 1=below zero). The next three digits in the group "017" give the temperature in degrees and tenths of a degree Celsius, −1.7 °C (28.9 °F). The last four digits "1017" indicate the dew point, −1.7 °C (28.9 °F). Note: ASOS software, as of this update, uses whole degrees in °F to compute the °C values in this group.
  • = indicates the end of the METAR.

In Canada, RMK is followed by a description of the cloud layers and opacities, in eighths (oktas). For example, CU5 would indicate a cumulus layer with 58 opacity.[12]

Cloud reporting

Cloud coverage is reported by the number of 'oktas' (eighths) of the sky that is occupied by cloud.

This is reported as:[13]

AbbreviationMeaning
SKC"No cloud/Sky clear" used worldwide but in North America is used to indicate a human generated report[14][15]
NCD"Nil Cloud detected" automated METAR station has not detected any cloud, either due to a lack of it, or due to an error in the sensors
CLR"No clouds below 12,000 ft (3,700 m) (U.S.) or 25,000 ft (7,600 m) (Canada)", used mainly within North America and indicates a station that is at least partly automated[14][15]
NSC"No (nil) significant cloud", i.e., none below 5,000 ft (1,500 m) and no TCU or CB. Not used in North America.
FEW"Few" = 1–2 oktas
SCT"Scattered" = 3–4 oktas
BKN"Broken" = 5–7 oktas
OVC"Overcast" = 8 oktas, i.e., full cloud coverage
VVClouds cannot be seen because of fog or heavy precipitation, so vertical visibility is given instead.

Flight categories in the U.S.

METARs can be expressed concisely using so-called aviation flight categories, which indicates what classes of flight can operate at each airport by referring to the visibility and ceiling in each METAR. Four categories are used in the U.S.:[16]

CategoryVisibilityCeiling
VFR> 5 miand > 3000 ft AGL
Marginal VFRBetween 3 and 5 miand/or Between 1,000 and 3,000 ft AGL
IFR1 mi or more but less than 3 miand/or 500 ft or more but less than 1,000 ft
Low IFR< 1 miand/or < 500 ft

METAR WX codes

METAR abbreviations used in the WX section. Remarks section will also include began and end times of the weather events.[17]

Codes before remarks will be listed as "-RA" for "light rain". Codes listed after remarks may be listed as "RAB15E25" for "Rain began at 15 minutes after the top of the last hour and ended at 25 minutes after the top of the last hour."

Type Abbreviation Meaning Abbreviation Meaning
Intensity-Light intensityblankModerate intensity
Intensity+Heavy intensityVCIn the vicinity
DescriptorMIShallow (French: Mince)PRPartial
DescriptorBCPatches (French: Bancs)DRLow drifting
DescriptorBLBlowingSHShowers
DescriptorTSThunderstormFZFreezing
PrecipitationRARainDZDrizzle
PrecipitationSNSnowSGSnow Grains
PrecipitationICIce CrystalsPLIce Pellets
PrecipitationGRHail (in the US includes Small Hail) (French: Grêle)GSSnow Pellets and/or Small Hail (not in the US) (French: Grésil)
PrecipitationUPUnknown Precipitation
ObscurationFGFogVAVolcanic Ash
ObscurationBRMist (French: Brume)HZHaze
ObscurationDUWidespread DustFUSmoke (French: Fumée)
ObscurationSASandPYSpray
OtherSQSquallPODust (French: Poussière) or Sand Whirls
OtherDSDuststormSSSandstorm
OtherFCFunnel Cloud
TimeBBegan At TimeEEnded At Time
Time2 digitsMinutes of current hour4 digitsHour/Minutes Zulu Time

Notes

1.^ In the US Small Hail is included with regular hail and the Remarks section is used saying "GR LESS THAN 1/4".[18] Elsewhere hail is GR when it is 5 mm or greater[19] Outside of the US when the hail is less than 5 mm the code GS is used.[19])

U.S. METAR abbreviations

The following METAR abbreviations are used in the United States; some are used worldwide:[6]

METAR and TAF Abbreviations and Acronyms:

Abbreviation Meaning Abbreviation Meaning
$maintenance check indicator/indicator that visual range data follows; separator between temperature and dew point data.
ACCaltocumulus castellanusACFT MSHPaircraft mishap
ACSLaltocumulus standing lenticular cloudALPairport location point
ALQDSall quadrants (official)ALQSall quadrants (unofficial)
AO1automated station without precipitation discriminatorAO2automated station with precipitation discriminator
APCHapproachAPRNTapparent
APRXapproximatelyATCTairport traffic control tower
AUTOfully automated reportCcenter (with reference to runway designation)
CAcloud-air lightningCBcumulonimbus cloud
CBMAMcumulonimbus mammatus cloudCCcloud-cloud lightning
CCSLcirrocumulus standing lenticular cloudcdcandela
CGcloud-ground lightningCHIcloud-height indicator
CHINOsky condition at secondary location not availableCIGceiling
CONScontinuousCORcorrection to a previously disseminated observation
DOCDepartment of CommerceDODDepartment of Defense
DOTDepartment of TransportationDSIPTGdissipating
DSNTdistantDVRdispatch visual range
Eeast, ended, estimated ceiling (SAO)FAAFederal Aviation Administration
FIBIfiled but impracticable to transmitFIRSTfirst observation after a break in coverage at manual station
FMH-1Federal Meteorological Handbook No.1, Surface Weather Observations & Reports (METAR)FMH2Federal Meteorological Handbook No.2, Surface Synoptic Codes
FROPAfrontal passageFROINfrost on the indicator
FRQfrequentFTfeet
FZRANOfreezing rain sensor not availableGgust
HLSTOhailstoneICAOInternational Civil Aviation Organization
INCRGincreasingINTMTintermittent
KTknotsLleft (with reference to runway designation)
LASTlast observation before a break in coverage at a manual stationLSTlocal standard time
LTGlightningLWRlower
Mminus, less thanMAXmaximum
METARroutine weather report provided at fixed intervalsMINminimum
MOVmoved/moving/movementMTmountains
NnorthN/Anot applicable
NCDCNational Climatic Data CenterNEnortheast
NOSNational Ocean ServiceNOSPECIno SPECI reports are taken at the station
NOTAMNotice to AirmenNWnorthwest
NWSNational Weather ServiceOCNLoccasional
OFCMOffice of the Federal Coordinator for MeteorologyOHDoverhead
OVRoverPindicates greater than the highest reportable value
PCPNprecipitationPK WNDpeak wind
PNOprecipitation amount not availablePRESpressure
PRESFRpressure falling rapidlyPRESRRpressure rising rapidly
PWINOprecipitation identifier sensor not availableRright (with reference to runway designation), runway
RTDRoutine Delayed (late) observationRVreportable value
RVRRunway visual rangeRVRNORVR system values not available
RWYrunwaySsouth
SCSLstratocumulus standing lenticular cloudSEsoutheast
SFCsurface, i.e., ground level)SLPsea-level pressure
SLPNOsea-level pressure not availableSMstatute miles
SNINCRsnow increasing rapidlySOGsnow on the ground
SPECIan unscheduled report taken when certain criteria have been metSTNstation
SWsouthwestTCUtowering cumulus
TSthunderstormTSNOthunderstorm information not available
TWRtowerUNKNunknown
UTCCoordinated Universal TimeVvariable
VISvisibilityVISNOvisibility at secondary location not available
VRvisual rangeVRBvariable
WwestWG/SOWorking Group for Surface Observations
WMOWorld Meteorological OrganizationWNDwind
WSwind shearWSHFTwind shift
ZZulu, i.e., Coordinated Universal Time

U.S. METAR numeric codes

Additional METAR numeric codes listed after RMK.[17] [17]

CodeDescription
112346 hour maximum temperature. Follows RMK with five digits starting with 1. Second digit is 0 for positive and 1 for negative. The last 3 digits equal the temperature in tenths.

This example value equals −23.4 °C (−10 °F).

201236 hour minimum temperature. Follows RMK with five digits starting with 2. Second digit is 0 for positive and 1 for negative. The last 3 digits equal the temperature in tenths.

This example value equals 12.3 °C (54 °F).

4/012Total snow depth in inches. Follows RMK starting with 4/ and followed by 3 digit number that equals snow depth in inches.

This example value equals 12 inches of snow currently on the ground.

40234012324-hour maximum and minimum temperature. Follows RMK with nine digits starting with 4. The second and sixth digit equals 0 for positive for 1 for negative. Digits 3–5 equal the maximum temperature in tenths and the digits 7–9 equals the minimum temperature in tenths.

This example value equals 23.4 °C (74 °F) and 12.3 °C (54 °F).

520063 hour pressure tendency. Follows RMK with 5 digits starting with 5. The second digit gives the tendency. In general 0–3 is rising, 4 is steady and 5–8 is falling. The last 3 digits give the pressure change in tenths of a millibar in the last 3 hours.

This example indicates a rising tendency of 0.6 millibars (0.018 inHg).[20]

601233 or 6 hour precipitation amount. Follows RMK with 5 digits starting with 6. The last 4 digits are the inches of rain in hundredths. If used for the observation nearest to 00:00, 06:00, 12:00, or 18:00 UTC, it represents a 6-hour precipitation amount. If used in the observation nearest to 03:00, 09:00, 15:00 or 21:00 UTC, it represents a 3-hour precipitation amount.

This example shows 1.23 inches (31 mm) of rain.

7024624-hour precipitation amount. Follows RMK with 5 digits starting with 7. The last 4 digits are the inches of rain in hundredths.

This example shows 2.46 inches (62 mm) of rain.

8/765Cloud cover using WMO code. Follows RMK starting with 8/ followed by a 3 digit number representing WMO cloud codes.
98060Duration of sunshine in minutes. Follows RMK with 5 digits starting with 98. The last 3 digits are the total minutes of sunshine.

This example indicates 60 minutes of sunshine.

931222Snowfall in the last 6-hours. Follows RMK with 6 digits starting with 931. The last 3 digits are the total snowfall in inches and tenths.

This example indicates 22.2 inches (560 mm) of snowfall.

933021Liquid water equivalent of the snow (SWE). Follows RMK with 6 digits starting with 933. The last 3 digits are the total inches in tenths.

This example indicates 2.1 inches (53 mm) SWE.

WMO codes for cloud types

The following codes identify the cloud types used in the 8/nnn part. [17]

CodeLow CloudsMiddle CloudsHigh Clouds
0nonenonenone
1Cumulus
(fair weather)
Altostratus
(thin)
Cirrus
(filaments)
2Cumulus
(towering)
Altostratus
(thick)
Cirrus
(dense)
3Cumulonimbus
(no anvil)
Altocumulus
(thin)
Cirrus
(often with Cumulonimbus)
4Stratocumulus
(from Cumulus)
Altocumulus
(patchy)
Cirrus
(thickening)
5Stratocumulus
(not Cumulus)
Altocumulus
(thickening)
Cirrus / Cirrostratus
(low in sky)
6Stratus or Fractostratus
(fair)
Altocumulus
(from Cumulus)
Cirrus / Cirrostratus
(hi in sky)
7Fractocumulus / Fractostratus
(bad weather)
Altocumulus
(with Altocumulus,
Altostratus, Nimbostratus)
Cirrostratus
(entire sky)
8Cumulus and StratocumulusAltocumulus
(with turrets)
Cirrostratus
(partial)
9Cumulonimbus
(thunderstorm)
Altocumulus
(chaotic)
Cirrocumulus or
Cirrocumulus / Cirrus / Cirrostratus
/not validabove overcastabove overcast

See also

References

  1. "Chapter 7". Aeronautical Information Manual. Archived from the original on 2009-09-05. Retrieved 2007-12-01.
  2. METAR (MEteorological Terminal Aviation Routine Weather Report) Station Network at the Centre for Environmental Data Archival
  3. Aerodrome Meteorological Observation and Forecast Study Group (AMOFSG) at ICAO
  4. "782 – Aerodrome reports and forecasts: A user's handbook to the codes". World Meteorological Organization. Retrieved 2009-09-23.
  5. Air Force Manual 15-111 Archived 2011-05-27 at the Wayback Machine
  6. METAR/TAF List of Abbreviations and Acronyms.
  7. Pilot's Handbook of Aeronautical Knowledge
  8. Get Met 2012 Archived 2012-05-18 at the Wayback Machine published by the UK Met Office, p 13
  9. Key to Aerodrome Forecast (TAF) and Aviation Routine Weather Report (METAR)
  10. Precipitation discriminators are electrically heated at sub-freezing temperatures to calculate the water equivalent of frozen precipitation and snow accumulation.
  11. Key to METAR Surface Weather Observations
  12. Environment Canada (2012). "MMmetar.html". meteocentre.com. Retrieved March 28, 2012.
  13. Aerodrome Weather Report – World Meteorological Organization Archived 2012-02-24 at the Wayback Machine
  14. Sky Condition Group NsNsNshshshs or VVhshshs or SKC Department of Atmospheric Sciences at Texas A&M University
  15. MET – 3.0 Appendices Archived 2011-10-31 at the Wayback Machine
  16. "Aeronautical Information Manual, Section 7-1-7, 'Categorical Outlooks'". Federal Aviation Administration. Archived from the original on 2012-07-26.
  17. Key to Decoding the U.S. METAR Observation Report
  18. METAR/SPECI Reporting Changes for Snow Pellets (GS) and Hail (GR)
  19. 10.2 Section II - hourly observations "UTC". See 10.2.10 Column 32 - weather and obstructions to vision
  20. METAR Help
Decoding
Format specifications
  • OFCM.gov — U.S. Federal Meteorological Handbook No. 1 — Surface Weather Observations and Reports (September 2005). Complete documentation on the METAR format, PDF.
  • metar.NOAA.gov — Information on METAR and TAF reports. Also provides a link to current METARs and cycle files.
  • WMO documentation on METAR format
Software libraries
Current reports
Current and historical reports
  • Wunderground.com — searchable by location, can view historical METARs by location.
Wind roses based on METAR data
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