METAR

About 6 pages (1,711 words)

METAR (aviation routine weather report) 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. METAR reports typically come from airports or permanent weather observation stations. Reports are typically generated once an hour; however, if conditions change significantly, they may be updated in special reports called SPECI's. Some reports are encoded by an automated airport weather station located at airports, military bases and other sites. Some locations still use augmented observations, which are recorded by digital sensors and encoded via software, but are 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 their being transmitted.

1 History
- 1.1 Naming
2 Information contained in a METAR
3 Regulation
4 International METAR Code
5 United States/Canada METAR Code
6 See also
7 References
8 External links

History

The METAR format was introduced 1 January 1968 internationally and has been modified several 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 Meterological Organization's publication No. 782 "Aerodrome Reports and Forecasts" contains the base METAR code as adopted by the WMO member countries.^[1]

Naming

The word METAR originated from the French, "message d’observation météorologique régulière pour l’aviation," and is thought to be a contraction from the french words, MÉTéorologique ("Weather") Aviation Régulière ("Routine"). The Federal Aviation Administration (FAA) defines a METAR as an aviation routine weather report in the Aeronautical Informational Manual and may therefore consider it erroneous to attempt to redefine METAR with incorrect terminology such as METeorological Aerodrome Report.^[2] The FAA and National Oceanic and Atmospheric Administration (NOAA) specifically define a METAR as an aviation routine weather report, which is an approximate translation of the historical French description.

Information contained in a METAR

A typical METAR report contains data for the temperature, dew point, wind speed and direction, precipitation, cloud cover and heights, visibility, and barometric pressure. A METAR report may also contain information on precipitation amounts, lightning, and other information that would be of interest to pilots or meteorologists such as Colour States. 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 METAR reports, reporting forecast weather rather than current weather, are TAFs. METARs and TAFs are used in VOLMET broadcasts.

Regulation

METAR code is regulated by Federal Meteorological Handbook No. 1 (FMH-1) and the World Meteorological Organization (WMO) aviation routine weather reports (FM-15 METAR) and aviation selected special weather reports (FM-16 SPECI) codes.

International METAR Code

The following is an example METAR from Burgas Airport in Burgas, Bulgaria, and was taken on February 4, 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 day of the month is the 4th and the time of day is 1600 Zulu time, 4:00PM Greenwich Mean Time, or 6:00PM Eastern European Time.
12003MPS indicates the wind direction is from 120 degrees true (east-southeast) at a speed of 3 meters per second.
310V290 indicates the wind direction is varying from 310 degrees true (northwest) through 120 degrees true (east-southeast) to 290 degrees true (west-northwest).
1400 indicates the prevailing visibility is 1400 metres.
R04/P1500N indicates the Runway visual range (RVR) along Runway 04 is 1500 meters and not changing significantly.
R22/P1500U indicates RVR along Runway 22 is 1500 meters and rising.
+SN indicates snow is falling at a heavy intensity.
BKN022 indicates a broken cloud layer at 2,200 feet above ground level (agl).
OVC050 indicates an unbroken cloud layer (overcast) at 5,000 feet above ground level.
M04/M07 indicates the temperature is minus 4 degrees Celsius and the dewpoint is minus 7 degrees Celsius.
Q1020 indicates the current barometric pressure extrapolated to sea level is 1020 millibars.
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 runway status. Format: abcdefgh ab=runway heading, c=nature of coating (4=dry snow), d=surface covered in percent (9= 51-100% of rwy covered), ef=thickness of coating in millimeters (// stands for either not measurable or not affecting usage of rwy) gh=braking index (91=bad braking index i.e grip on rwy)
CAVOK indicates Ceiling And Visibility OKay (no cloud below 5000 feet, a visibility of 6 Statute Miles or more and no precipitation, thunderstorms, shallow fog, or low drifting snow)
= indicates the end of the METAR report

United States/Canada METAR Code

North American metars deviate slightly from the WMO (who write the code on behalf of the International Civil Aviation Organization (ICAO)) FM 15-XII code. Details listed in the FAA's Aeronautical Information Manual (AIM). This METAR example is from Trenton-Mercer Airport near Trenton, New Jersey, and was taken on December 5, 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=

METAR indicates that the following is a standard hourly observation.
KTTN indicates the report came from Trenton-Mercer Airport, near the city of Trenton, New Jersey in the continental United States.
051853Z indicates the day of the month is the 5th and the time of day is 1853 Zulu time, 6:53PM Greenwich Mean Time, or 1:53PM Eastern Standard Time.
04011KT indicates the wind direction is from 40 degrees true (northeast) at a speed of 11 knots (approximately 13 statute miles per hour).
1/2SM indicates the prevailing visibility is 0.5 statute miles.
VCTS indicates there is a thunderstorm in the vicinity (within 10SM, but beyond 5SM).
SN indicates snow is falling at a moderate intensity.
FZFG indicates the presence of freezing fog.
BKN003 indicates a broken cloud layer at 300 feet above ground level.
OVC010 indicates an overcast cloud layer at 1,000 feet above ground level.
M02/M02 indicates the temperature is minus 2 degrees Celsius and the dewpoint is minus 2 degrees Celsius.
A3006 indicates the altimeter setting is 30.06 inches of mercury.

Note that what follows is not part of the international format. This example is particular to the United States, a format not shared with Canada.

RMK indicates the remarks section follows.
AO2 indicates that the station has an automated precipitation sensor.^[3]
TSB40 indicates the thunderstorm began 40 minutes after the top of the hour at 1840 Zulu time, 6:40PM Greenwich Mean Time, or 1:40PM Eastern Standard Time.
SLP176 indicates the current barometric pressure extrapolated to sea level is 1017.6 millibars.
P0002 indicates that 0.02 inches of liquid-equivalent precipitation accumulated during the last hour.
T10171017 indicates the temperature is 29 degrees Fahrenheit (converted to minus 1.7 degrees Celsius) and the dewpoint is 29 degrees Fahrenheit (converted to minus 1.7 degrees Celsius).
= indicates the end of the METAR report.

References

^ 782 - Aerodrome reports and forecasts: A user's handbook to the codes. World Meteorological Organization. Retrieved on 2007-12-02.
^ Chapter 7. Aeronautical Information Manual. Retrieved on 2007-12-01.
^ Key to METAR Surface Weather Observations

2. METAR and TAF Abbreviations 3. FAA Explanation of METARs (.pdf)

• • e Meteorological data and variables
Atmospheric pressure · Baroclinity · Cloud · Convection · CAPE · CIN · Dew point · Heat index · Humidex · Humidity · Lifted index · Lightning · Pot T · Precipitation · Sea surface temperature · Surface solar radiation · Surface weather analysis · Temperature · Theta-e · Visibility · Vorticity · Wind chill · Water vapor · Wind

• • e

Meteorological instrumentation and equipment (Earth based)

• • e

Meteorological Observation Systems and Weather Stations (Earth based)

Argo | Global Atmosphere Watch | Aircraft Communication Addressing and Reporting System (ACARS) | Aircraft Meteorological Data Relay (AMDAR) | Aircraft report (AIREP} | Automatic weather station | Automated airport weather station | Coastal-Marine Automated Network (C-MAN) | Global Sea Level Observing System | Meteorological Aerodrome Report (METAR) | NEXRAD radar | Pilot report (PIREP) | Remote Automated Weather Stations (RAWS) | SST buoys | TAMDAR | Tide gauges | Weather buoys | Hurricane Hunters | Dropsonde | Weather balloon | Weather ship

External links

Format specifications

OFCM.gov - Complete documentation on the METAR format
NOAA.gov - Information on METAR and TAF reports. Also provides a link to current metar reports and cycle files.

Software libraries

Perl modules for parsing METAR reports at the CPAN website
PhpWeather is a PHP application (with a GNU GPL licence) that parses METAR reports.
pymetar python library for METAR fetching and parsing