METAR

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METAR is a format for reporting weather information. A METAR weather report is predominantly used by pilots in fulfillment of a part of a pre-flight weather briefing, and by meteorologists, who use aggregated METAR information to assist in weather forecasting.

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

Origin[edit]

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[edit]

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 World Meteorological Organization's (WMO) publication No. 782 "Aerodrome Reports and Forecasts" contains the base METAR code as adopted by the WMO member countries.[1]

Naming[edit]

The United States Federal Aviation Administration (FAA) lays down the definition in its publication the Aeronautical Information Manual as aviation routine weather report[2] while the international authority for the code form, the 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 or Meteorological Aerodrome Report.

Information contained in a METAR[edit]

A typical METAR contains data for the temperature, dew point, wind speed and direction, 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[edit]

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 US national differences from the WMO/ICAO model) under the Federal Meteorological Handbook No. 1 (FMH-1), which itself has paved the way for the US Air Force Manual 15-111[3] on Surface Weather Observations, being the authoritative document for the US 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[edit]

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.[4][5]

Example METAR codes[edit]

International METAR codes[edit]

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 12003MPS 310V290 1400 R04/P1500N R22/P1500U +SN BKN022 OVC050 M04/M07 Q1020 NOSIG 9949//91=

North American METAR codes[edit]

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=[7]

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

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 5/8ths opacity.[9]

Cloud reporting[edit]

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

This is reported as:[10]

AbbreviationMeaning
SKC'No cloud/Sky clear' used worldwide but in North America is used to indicate a human generated report[11][12]
CLR'No clouds below 12,000 ft (3,700 m) (US) or 10,000 ft (3,000 m) (Canada)' used mainly within North America and indicates a station that is at least partly automated[11][12]
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[edit]

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:[13]

CategoryVisibilityCeiling
VFR> 5 miand > 3,000 ft
Marginal VFRBetween 3 and 5 miand/or Between 1,000 and 3,000 ft
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[edit]

METAR abbreviations used in the WX section. Remarks section will also include began and end times of the weather events.[14]

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."

TypeAbbreviationMeaningAbbreviationMeaning
Intensity-Light intensityblankModerate intensity
Intensity+Heavy intensityVCIn the vicinity
DescriptorMIShallowPRPartial
DescriptorBCPatchesDRLow drifting
DescriptorBLBlowingSHShowers
DescriptorTSThunderstormFZFreezing
PrecipitationRARainDZDrizzle
PrecipitationSNSnowSGSnow Grains
PrecipitationICIce CrystalsPLIce Pellets
PrecipitationGRHailGSSmall Hail
PrecipitationUPUnknown Precipitation
ObscurationFGFogVAVolcanic Ash
ObscurationBRMistHZHaze
ObscurationDUWidespread DustFUSmoke
ObscurationSASandPYSpray
OtherSQSquallPODust or Sand Whirls
OtherDSDuststormSSSandstorm
OtherFCFunnel Cloud
TimeBBegan At TimeEEnded At Time
Time2 digitsMinutes of current hour4 digitsHour/Minutes Zulu Time

US METAR abbreviations[edit]

The following are METAR abbreviations used in the United States, however some are used worldwide:[4]

METAR and TAF Abbreviations and Acronyms:

AbbreviationMeaningAbbreviationMeaning
$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 SurveyNOSPECIno 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 availablePRESAtmospheric pressure
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

US METAR numeric codes[edit]

Additional METAR numeric codes listed after RMK.[14] [15]

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.

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 follow 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 millibars in the last 3 hours.

This example indicates a rising tendency of 0.6 millibars.[16]

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 00UTC, 06UTC, 12UTC, or 18UTC, it represents a 6-hour precipitation amount. If used in the observation nearest to 03UTC, 09UTC, 15UTC or 21UTC, it represents a 3-hour precipitation amount.

This example shows 1.23 inches 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 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 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 SWE.

WMO codes for cloud types[edit]

The following codes identify the cloud types used in the 8/nnn part. [14]

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
(T-storm)
Altocumulus
(chaotic)
Cirrocumulus or
Cirrocumulus / Cirrus / Cirrostratus
/not validabove overcastabove overcast

See also[edit]

References[edit]

External links[edit]

Decoding
Format specifications
Software libraries
Current reports
Current and historical reports