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. Today, according to the advancement of technology in civil aviation, the METAR is sent as IWXXM model.[1]
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.
In its publication the Aeronautical Information Manual, the United States Federal Aviation Administration (FAA) describes the report as aviation routine weather report,[2] while the international authority for the code form, the World Meteorological Organization (WMO), describes it as the 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[3] or Meteorological Aerodrome Report.[4]
METARs typically come from airports or permanent weather 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. Some stations make regular reports more frequently, such as Pierce County Airport (ICAO code: KPLU) which issues reports three times per hour. 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.
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 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.[5]
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.
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[6] 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.
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.[7] [8]
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=
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=[10]
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 opacity.[13]
Cloud coverage is reported by the number of 'oktas' (eighths) of the sky that is occupied by cloud.
This is reported as:[14]
| Abbreviation | Meaning | |
|---|---|---|
| SKC | "No cloud/Sky clear" used worldwide but in North America is used to indicate a human generated report[15] [16] | |
| 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 12000feet (U.S.) or 25000feet (Canada)", used mainly within North America and indicates a station that is at least partly automated | |
| NSC | "No (nil) significant cloud", i.e., none below 5000feet 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 | |
| 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. |
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.:[17]
| Category | Visibility | Ceiling | |
|---|---|---|---|
| > 5 mi | and > 3000 ft AGL | ||
| Marginal VFR | Between 3 and 5 mi | and/or Between 1,000 and 3,000 ft AGL | |
| 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 began and end times of the weather events.[18] 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), SHGSSN etc.
| Type | Meaning | ||
|---|---|---|---|
| Intensity | - | Light intensity | |
| Intensity | (blank) | Moderate intensity | |
| Intensity | + | Heavy intensity | |
| Descriptor | VC | In the vicinity (5-10 mi / 8-16 km from station); 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 as Thunder) | |
| Descriptor | FZ | ||
| 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)[19] [20] Elsewhere hail is GR when it is 5 mm or greater[21] Outside of the US when the hail is less than 5 mm the code GS is used.) | |
| Precipitation | GR | Hail [French: ''Grêle''] (in the US includes Small Hail) | |
| 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) | |
| Obscuration | HZ | Haze (due to dry particulates, visibility between 1 and 5 km) | |
| Obscuration | VA | Volcanic Ash | |
| Obscuration | DU | Widespread Dust | |
| Obscuration | FU | Smoke [French: ''Fumée''] | |
| Obscuration | SA | Sand | |
| Obscuration | PY | Spray | |
| Other | SQ | Squall | |
| Other | PO | Dust [French: ''Poussière''] or Sand 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:[7]
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 | ACFT MSHP | aircraft mishap | |
| ACSL | 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 | CB | cumulonimbus cloud | |
| CBMAM | CC | cloud-cloud lightning | |
| CCSL | 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 | L | left (with reference to runway designation) | |
| LAST | last observation before a break in coverage at a manual station | LST | local standard time |
| LTG | 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 | NE | northeast | |
| NOS | NOSPECI | no SPECI reports are taken at the station | |
| NOTAM | NW | northwest | |
| NWS | 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 | 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 | TSNO | thunderstorm information not available | |
| TWR | 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 | WND | wind | |
| WS | WSHFT | wind shift | |
| Z | Zulu, i.e., Coordinated Universal Time |
Additional METAR numeric codes listed after RMK.[18]
| 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 12.3C. | |
| 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 23.4C and 12.3C. | |
| 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 0.6mb.[22] | |
| 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 1.23inches 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 2.46inches 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 22.2inches 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 2.1inches SWE. |
The following codes identify the cloud types used in the 8/nnn part.[18]
| 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 (thunderstorm) | Altocumulus (chaotic) | Cirrocumulus or Cirrocumulus / Cirrus / Cirrostratus | |
| / | not valid | above overcast | above overcast |