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METAR is a format for reportingweather information. A METAR weather report is predominantly used byaircraft pilots, and bymeteorologists, who use aggregated METAR information to assist inweather forecasting.
Raw METAR is highly standardized through theInternational Civil Aviation Organization (ICAO), which enables it to be understood throughout most of the world.
In its publication theAeronautical Information Manual (AIM), the United StatesFederal Aviation Administration (FAA) describes the report asaviation routine weather report,[1] while the international authority for the code form, theWorld Meteorological Organization (WMO), describes it as theaerodrome routine meteorological report. TheNational Oceanic and Atmospheric Administration (part of theUnited States Department of Commerce) and the United Kingdom'sMet Office both employ the definition used by the FAA. METAR is also known asMeteorological Terminal Aviation Routine Weather Report[2] orMeteorological Aerodrome Report.[3]
METARs typically come fromairports or other permanentweather observation stations. Reports are generated once an hour or half-hour at most stations, but if conditions change significantly at a staffed location, a report known as a special (SPECI) may be issued.[4]: 2 [note 1] Some stations make regular reports more frequently, such asPierce County Airport (ICAO code: KPLU) which issues reports three times per hour.[5] In addition to METARs and SPECIs, ASOS One-Minute Observations (OMO) are updated once a minute. OMOs can be in various formats, including the METAR format.[4]: 3
Some METARs are encoded byautomated 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. In the United States, prior to mid-1990s, most observations are made manually, but today the vast majority are automated or augmented observations.[4]: 2
The METAR format was introduced internationally on 1 January 1968, 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 1989Geneva agreement. The WMO's publication No. 782 "Aerodrome Reports and Forecasts" contains the base METAR code as adopted by the WMO member countries.[6]
A typical METAR contains data for the airport identifier, time of observation,wind direction and speed,visibility, current weather phenomena such asprecipitation,cloud cover and heights,temperature,dew point, andbarometric pressure. This information forms the body of the report, consisting a maximum of 11 groups of information.[4]: 5 A METAR may also contain information on precipitation amounts,lightning, and other information that would be of interest to pilots or meteorologists such as apilot report or PIREP,colour states andrunway visual range (RVR). These may be provided in coded or plain language and appended to the end of the METAR as remarks.[4]: 6
In addition, a short period forecast called aTREND 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 aTerminal Aerodrome Forecast (TAF).
The complement to METARs, reporting forecast weather rather than current weather, are TAFs. METARs and TAFs are used inVOLMET broadcasts.
Cloud coverage is reported by the number of "oktas" (eighths) of the sky that is occupied by cloud. Automated substation substitutes time averaging of sensor data gathered during 30-minute period prior to reporting.[4]: 2, 4
This is reported as:[7]
| Abbreviation | Meaning |
|---|---|
| SKC | "No cloud/Sky clear" used worldwide but in North America is used to indicate a human generated report[8][9] |
| 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) (US) or 25,000 ft (7,600 m) (Canada)", used mainly within North America and indicates a station that is at least partly automated[8][9] |
| NSC | "No (nil) significant cloud",i.e., none below 5,000 ft (1,500 m) and noTCU orCB. 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 |
| TCU | Towering cumulus cloud,e.g., SCT016TCU |
| CB | Cumulonimbus cloud,e.g., FEW015CB |
| VV | "Vertical visibility" = clouds cannot be seen because of fog or heavy precipitation, so vertical visibility is given instead. |
The following codes identify thecloud types used in the 8/nnn part of RMK.[10]
| 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 withcumulonimbus) |
| 4 | Stratocumulus (fromcumulus) | Altocumulus (patchy) | Cirrus (thickening) |
| 5 | Stratocumulus (notcumulus) | Altocumulus (thickening) | Cirrus /cirrostratus (low in sky) |
| 6 | Stratus orFractostratus (fair) | Altocumulus (fromcumulus) | Cirrus /cirrostratus (hi in sky) |
| 7 | Fractocumulus /fractostratus (bad weather) | Altocumulus (withaltocumulus, altostratus,nimbostratus) | Cirrostratus (entire sky) |
| 8 | Cumulus andstratocumulus | Altocumulus (with turrets) | Cirrostratus (partial) |
| 9 | Cumulonimbus (thunderstorm) | Altocumulus (chaotic) | Cirrocumulus or Cirrocumulus /cirrus /cirrostratus |
| / | not valid | above overcast | above overcast |
Wind observation measures the horizontal vector component of the wind, which includes both direction and speed. These are determined by evaluating the measurement over a 2-minute period.[4]: 24–10
The wind direction is coded with the first three digits in tens of degrees relative to thetrue north. If wind speed is less than or equal to 6 kn (11 km/h; 6.9 mph), the wind direction will be displayed as variable or "VRB". If the wind speed is greater than 6 knots, but the direction varies more than 60° in the past 2 minutes, METAR will report the range of wind direction. For example,21010KT 180V240 suggests the wind was variable from 180° to 240° at 10 knots.[4]: 10
Immediately after the wind direction is the wind speed, coded in two or three digits measured in knots, km/h or m/s. If during past 10 minutes, the weather station detects more than 10 kn (19 km/h; 12 mph) between minimum and maximum windspeed, METAR determines awind gust exists and reports the maximum instantaneous windspeed.[4]: 10
If the air is motionless, the wind will be reported as calm and coded as00000KT.[4]: 10
Visibility measures the atmospheric opacity. It is the greatest distance where at least half of the horizon circle can be seen from the surface.[4]: 11
Runway visual range (RVR) is an instrument-derived measurement that suggests the horizontal distance an observer may see down the runway. In the US, for stations with RVR reporting capacity, this information is omitted from the METAR unless the visibility is at or below 1 mi (1.6 km), or the designated instrument runway's RVR is at or below 6,000 ft (1,800 m). RVR of up to four designated runways may be reported, depending on the country.[4]: 11
METAR code is regulated by theWorld 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 theFederal Meteorological Handbook No. 1 (FMH-1), which paved the way for theUS Air Force Manual 15-111[11] 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.
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 — ICAO allows member countries to modify METAR code for use in their particular countries, as long as ICAO is notified.[4]: 5
The two examples which follow illustrate the primary differences between the international and the North American METAR variations.[10][12][page needed]
The following is an example METAR fromBurgas Airport inBurgas,Bulgaria. It was taken on 4 February 2005 at 16:00Coordinated Universal Time (UTC).
METAR LBBG 041600Z 12012MPS 090V150 1400 R04/P1500N R22/P1500U +SN BKN022 OVC050 M04/M07 Q1020 NOSIG 8849//91=
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'sAeronautical Information Manual (AIM), but the non-compliant elements are mostly based on the use of non-standard units of measurement. This METAR example is fromTrenton-Mercer Airport nearTrenton,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=[14]
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 with5⁄8 opacity.[16]
METARs can be expressed concisely using so-calledaviation 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 US:[17]
| Category | Visibility | Ceiling |
|---|---|---|
| VFR | > 5 mi | and > 3000 ft AGL |
| Marginal VFR | Between 3 and 5 mi | and/or between 1,000 and 3,000 ft AGL |
| 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 abbreviations used in the weather and events section. Remarks section will also include begin and end times of the weather events.[10] 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."
Combinations of two precipitation types are accepted;e.g., RASN (rain and snow mixed), SHGSSNetc. If more than one type of weather is present, METAR will report in the following order:[4]: 13
| Type | Abbr. | Meaning |
|---|---|---|
| Intensity | - | Light intensity |
| Intensity | (blank) | Moderate intensity |
| Intensity | + | Heavy intensity |
| Descriptor | VC | In the vicinity (5–10mi / 8–16km fromstation); visible phenomena: TS, SH, FG, DS, SS, VA, PO, FC, BLSN, BLDU, BLSA |
| Descriptor | RE | Recent hour's most important past phenomenon with residues: TS, RA, FZRA, SN, BLSN, GR, GS, PL (e.g.:METAR ... Q1010 RERA=) |
| Descriptor | MI | Shallow[French:Mince] (fog descriptor) |
| Descriptor | PR | Partial (fog descriptor) |
| Descriptor | BC | Patches[French:Bancs] (fog descriptor) |
| Descriptor | DR | Low drifting below eye level; including:DRSN, DRSA, DRDU |
| Descriptor | BL | Blowing at or above eye level; including:BLSN, BLSA, BLDU |
| Descriptor* | SH | Showers (*also without precipitation: VCSH) |
| Descriptor* | TS | Thunderstorm (*also without precipitation: VCTS, RETS or asthunder) |
| Descriptor | FZ | Freezing; including:FZDZ,FZRA,FZFG |
| Precipitation | DZ | Drizzle |
| Precipitation | RA | Rain |
| Precipitation | SN | Snow (snowflakes) |
| Precipitation | SG | Snow grains |
| Precipitation | GS | Graupel[French:Grésil], snow pellets and/or small hail (not in the US).[note 3][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]) |
| Precipitation | GR | Hail[French:Grêle] (in the US includes small hail)[note 3] |
| Precipitation | PL | Ice pellets |
| Precipitation | IC | Ice crystals |
| Precipitation | UP | Unknown precipitation |
| Obscuration | FG | Fog (visibility less than 1 km) |
| Obscuration | BR | Mist[French:Brume] (due to water droplets, visibility between 1 and 5 km)[note 4] |
| Obscuration | HZ | Haze (due to dry particulates, visibility between 1 and 5 km)[note 4][4]: 3 |
| Obscuration | VA | Volcanic ash |
| Obscuration | DU | Widespread dust |
| Obscuration | FU | Smoke[French:Fumée] |
| Obscuration | SA | Sand |
| Obscuration | PY | Spray, only coded as BLPY |
| Other | SQ | Squall |
| Other | PO | Dust[French:Poussière] orsand whirls |
| Other | DS | Duststorm |
| Other | SS | Sandstorm |
| Other | FC | Funnel cloud |
| Time | B | Began at time |
| Time | E | Ended at time |
| Time | 2 digits | Minutes of current hour |
| Time | 4 digits | Hour/minutes Zulu time |
The following METAR abbreviations are used in the United States; some are used worldwide:[10]
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 standinglenticular 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 trafficcontrol tower |
| AUTO | fully automated report | C | center (with reference to runway designation) |
| CA | cloud-airlightning | CB | cumulonimbus cloud |
| CBMAM | cumulonimbusmammatus cloud | CC | cloud-cloud lightning |
| CCSL | cirrocumulus standinglenticular 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 Service | 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 | 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 standinglenticular 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 |
Additional METAR numeric codes listed after RMK.[10]
| 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 (−10 °F). |
| 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 followed 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 of a millibar in the last 3 hours. This example indicates a rising tendency of 0.6 millibars (0.018 inHg).[20] |
| 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 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. |
| 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 (62 mm) 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 (560 mm) 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 (53 mm) SWE. |
