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 common 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 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[3] 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[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=

  • 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 (the 4th) followed by the time of day (1600 Zulu time, which equals 4:00 pm Greenwich Mean Time).
  • 12003MPS indicates the wind direction is from 120° (east-southeast) at a speed of 3 MPS (5.8 KT; 6.7 mph; 11 km/h). Speed measurements can vary from knots (KT) or meters/second (MPS).
  • 290V310 indicates the wind direction is varying from 290° true (west northwest) to 310° true (northwest).
  • 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.
  • M04/M07 indicates the temperature is −4 °C (25 °F) and the dewpoint is −7 °C (19 °F). An M in front of the number indicates that the temperature/dew point is below zero (0) Celsius.
  • Q1020 indicates the current altimeter setting (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.
  • 9949//91 indicates the condition of the runway:
    • 99 indicates either a specific runway (e.g. 25 = Rwy 25 or 25L; adding 50 will indicate Right Runway) or all the airport's runways ("99"). 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 OKay, 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.[6]
  • = indicates the end of the METAR

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]

  • 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, 6:53PM GMT, 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.
  • FZFG indicates the presence of freezing fog.
  • BKN003 OVC010 indicates a broken (5/8 to 7/8 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 dewpoint is −2 °C (28 °F). An M in front of the number indicates that the temperature/dew point is "minus", i.e., below zero (0) Celsius.
  • 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.[8] Stations that aren't equipped with a rain/snow sensor are designated AO1.[9]
  • TSB40 indicates the thunderstorm began at 40 minutes past the hour at 1840 Zulu/UTC, 6:40 p.m. GMT, 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, −01.7 °C (28.9 °F). The last four digits "1017" indicate the dew point, −01.7 °C (28.9 °F). Note: ASOS software, as of this update, uses whole degrees in °F to compute the °C values in this group.[citation needed]
  • = 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 5/8 opacity.[10]

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:[11]

Abbreviation Meaning
SKC "No cloud/Sky clear" used worldwide but in North America is used to indicate a human generated report[12][13]
CLR "No clouds below 12,000 ft (3,700 m) (U.S.) or 10,000 ft (3,000 m) (Canada)", used mainly within North America and indicates a station that is at least partly automated[12][13]
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
VV Clouds 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:[14]

Category Visibility Ceiling
VFR > 3 mi and >  500 ft (below), > 1000 ft (above), > 2000 ft (horiz) [15]
Marginal VFR Between 3 and 5 mi and/or Between 1,000 and 3,000 ft
IFR 1 mi or more but less than 3 mi and/or 500 ft or more but less than 1,000 ft
Low IFR < 1 mi and/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.[16]

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 intensity blank Moderate intensity
Intensity + Heavy intensity VC In the vicinity
Descriptor MI Shallow PR Partial
Descriptor BC Patches DR Low drifting
Descriptor BL Blowing SH Showers
Descriptor TS Thunderstorm FZ Freezing
Precipitation RA Rain DZ Drizzle
Precipitation SN Snow SG Snow Grains
Precipitation IC Ice Crystals PL Ice Pellets
Precipitation GR Hail GS Small Hail
Precipitation UP Unknown Precipitation
Obscuration FG Fog VA Volcanic Ash
Obscuration BR Mist HZ Haze
Obscuration DU Widespread Dust FU Smoke
Obscuration SA Sand PY Spray
Other SQ Squall PO Dust or Sand Whirls
Other DS Duststorm SS Sandstorm
Other FC Funnel Cloud
Time B Began At Time E Ended At Time
Time 2 digits Minutes of current hour 4 digits Hour/Minutes Zulu Time

U.S. METAR abbreviations[edit]

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

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.
ACC altocumulus castellanus ACFT MSHP aircraft mishap
ACSL altocumulus standing lenticular cloud ALP airport location point
ALQDS All Quadrants (Official) ALQS All Quadrants (Unofficial)
AO1 automated station without precipitation discriminator AO2 automated station with precipitation discriminator
APCH approach APRNT apparent
APRX approximately ATCT airport traffic control tower
AUTO fully automated report C center (with reference to runway designation)
CA cloud-air lightning CB cumulonimbus cloud
CBMAM cumulonimbus mammatus cloud CC cloud-cloud lightning
CCSL cirrocumulus standing lenticular cloud cd candela
CG cloud-ground lightning CHI cloud-height indicator
CHINO sky condition at secondary location not available CIG ceiling
CONS continuous COR correction to a previously disseminated observation
DOC Department of Commerce DOD Department of Defense
DOT Department of Transportation DSIPTG dissipating
DSNT distant DVR dispatch visual range
E east, ended, estimated ceiling (SAO) FAA Federal Aviation Administration
FIBI filed but impracticable to transmit FIRST first observation after a break in coverage at manual station
FMH-1 Federal Meteorological Handbook No.1, Surface Weather Observations & Reports (METAR) FMH2 Federal Meteorological Handbook No.2, Surface Synoptic Codes
FROPA frontal passage FROIN Frost On The Indicator
FRQ frequent FT feet
FZRANO freezing rain sensor not available G gust
HLSTO hailstone ICAO International Civil Aviation Organization
INCRG increasing INTMT intermittent
KT KNOTS L left (with reference to runway designation)
LAST last observation before a break in coverage at a manual station LST Local Standard Time
LTG lightning LWR lower
M minus, less than MAX maximum
METAR routine weather report provided at fixed intervals MIN minimum
MOV moved/moving/movement MT mountains
N north N/A not applicable
NCDC National Climatic Data Center NE northeast
NOS National Ocean Survey NOSPECI no SPECI reports are taken at the station
NOTAM Notice to Airmen NW northwest
NWS National Weather Service OCNL occasional
OFCM Office of the Federal Coordinator for Meteorology OHD overhead
OVR over P indicates greater than the highest reportable value
PCPN precipitation PK WND peak wind
PNO precipitation amount not available PRES Atmospheric pressure
PRESFR pressure falling rapidly PRESRR pressure rising rapidly
PWINO precipitation identifier sensor not available R right (with reference to runway designation), runway
RTD Routine Delayed (late) observation RV reportable value
RVR Runway visual range RVRNO RVR system values not available
RWY runway S south
SCSL stratocumulus standing lenticular cloud SE southeast
SFC surface, i.e., ground level) SLP sea-level pressure
SLPNO sea-level pressure not available SM statute miles
SNINCR snow increasing rapidly SOG Snow on the ground
SPECI an unscheduled report taken when certain criteria have been met STN station
SW southwest TCU towering cumulus
TS thunderstorm TSNO thunderstorm information not available
TWR tower UNKN unknown
UTC Coordinated Universal Time V variable
VIS visibility VISNO visibility at secondary location not available
VR visual range VRB variable
W west WG/SO Working Group for Surface Observations
WMO World Meteorological Organization WND wind
WS wind shear WSHFT wind shift
Z Zulu, i.e., Coordinated Universal Time

U.S. METAR numeric codes[edit]

Additional METAR numeric codes listed after RMK.[16] [17]

Code Description
11234 6 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.

20123 6 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).

4/012 Total 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.

402340123 24 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).

52006 3 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.[18]

60123 3 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.

70246 24 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.

8/765 Cloud cover using WMO Code. Follows RMK starting with 8/ followed by a 3 digit number representing WMO cloud codes.
98060 Duration 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.

931222 Snowfall 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.

933021 Liquid 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. [16]

Code Low Clouds Middle Clouds High Clouds
0 none none none
1 Cumulus
(fair weather)
Altostratus
(thin)
Cirrus
(filaments)
2 Cumulus
(towering)
Altostratus
(thick)
Cirrus
(dense)
3 Cumulonimbus
(no anvil)
Altocumulus
(thin)
Cirrus
(often with Cumulonimbus)
4 Stratocumulus
(from Cumulus)
Altocumulus
(patchy)
Cirrus
(thickening)
5 Stratocumulus
(not Cumulus)
Altocumulus
(thickening)
Cirrus / Cirrostratus
(low in sky)
6 Stratus or Fractostratus
(fair)
Altocumulus
(from Cumulus)
Cirrus / Cirrostratus
(hi in sky)
7 Fractocumulus / Fractostratus
(bad weather)
Altocumulus
(with Altocumulus,
Altostratus, Nimbostratus)
Cirrostratus
(entire sky)
8 Cumulus and Stratocumulus Altocumulus
(with turrets)
Cirrostratus
(partial)
9 Cumulonimbus
(T-storm)
Altocumulus
(chaotic)
Cirrocumulus or
Cirrocumulus / Cirrus / Cirrostratus
/ not valid above overcast above overcast

See also[edit]

References[edit]

External links[edit]

Decoding
Format specifications
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