What is a METAR?

METAR (Meteorological Aerodrome Report) – Comprehensive Guide for Meteorology and Aviation

What is a METAR?

A METAR is a globally standardized format for reporting current weather observations at airports and aerodromes. Governed by the International Civil Aviation Organization (ICAO), the METAR provides up-to-the-minute, routine weather data critical for aviation safety, flight planning, and meteorological research. Reports are generated by either human observers or automated systems such as AWOS (Automated Weather Observing System) and ASOS (Automated Surface Observing System), ensuring consistent and reliable weather information across the world.

METARs are the universal language of surface weather for pilots, air traffic controllers, flight dispatchers, drone operators, and meteorologists. They are issued at least once an hour and updated immediately via special reports (SPECI) when significant weather changes occur.

The Importance of METARs in Aviation and Meteorology

Aviation Operations

Pilots rely on METARs for critical decisions affecting takeoff, landing, alternate airport selection, and route planning. The information in a METAR, wind, visibility, ceiling, and weather phenomena, directly impacts:

• Runway selection (based on wind direction and speed)
• Minimum equipment and fuel requirements
• Go/no-go decisions for VFR and IFR flights
• Alternate and emergency planning

A single METAR can be the deciding factor in delaying a flight, diverting to an alternate, or modifying approach procedures.

Air Traffic Control (ATC)

Controllers use METARs to:

• Assign runways according to wind and visibility
• Anticipate disruptions caused by adverse conditions (e.g., storms or fog)
• Communicate rapidly changing weather through SPECI alerts

Drone and UAS Operations

Regulations such as FAA Part 107 require drone pilots to check real-time weather before and during flight. METARs supply authoritative data on wind, visibility, precipitation, and temperature, directly affecting flight safety, battery performance, and legal compliance.

Meteorological Research

The global network of METAR stations offers a rich, high-frequency dataset for:

• Surface weather analysis and trend monitoring
• Calibration and validation of forecast models
• Climatological and severe weather studies

Safety and Compliance

Aviation authorities mandate adherence to weather minima based on METARs, ensuring all operations are conducted within safe and legal parameters.

Anatomy of a METAR Report

A METAR is a compact, coded message with elements in a strict sequence dictated by ICAO Doc 8896 and WMO No. 306. This format supports both rapid human understanding and automated processing.

Example METAR

METAR EGLL 241650Z 20012KT 9999 FEW025 SCT040 17/11 Q1013 NOSIG

Breakdown:

Decoding METAR Elements

1. Report Type

• METAR: Routine, hourly report
• SPECI: Special report for significant weather change
• COR: Corrected report

2. ICAO Station Identifier

Four-letter code identifying the aerodrome (e.g., EGLL for Heathrow, KJFK for New York JFK).

3. Date and Time

Formatted as DDHHMMZ (day, hour, minute in UTC/Zulu). Example: 241650Z = 24th day, 16:50 UTC.

4. Report Modifier

• AUTO: Automated observation
• COR: Correction to a previous report

5. Wind

Format: dddffKT (direction in degrees true, speed in knots), optional gusts as GggKT, or VRB for variable direction.

Examples:

• 21012KT: Wind from 210° at 12 knots
• 18008G18KT: From 180°, 8 knots gusting to 18 knots
• VRB03KT: Variable direction, 3 knots

6. Visibility

• US: In statute miles (SM), e.g., 10SM
• ICAO: In meters, e.g., 9999 (10km or more)
• RVR: Runway visual range (R36L/1200FT)

7. Weather Phenomena

Coded for intensity, descriptor, and phenomena:

Examples:

• +TSRA: Heavy thunderstorm rain
• –SN: Light snow
• BR: Mist

8. Sky Condition/Cloud Cover

Reported in oktas (eighths of sky):

Cloud altitude reported in hundreds of feet AGL (e.g., FEW025 = few clouds at 2,500 ft).

Suffixes:

• CB: Cumulonimbus (thunderstorm)
• TCU: Towering cumulus

9. Temperature and Dew Point

Degrees Celsius, separated by a slash.

• 17/11: 17°C, dew point 11°C
• M02/M08: Minus 2°C, minus 8°C

10. Altimeter Setting

• A2992: 29.92 inHg (US/Canada)
• Q1013: 1013 hPa (ICAO standard)

11. Remarks (RMK)

Supplementary info: sensor status, recent weather, runway conditions, etc.

Common METAR Abbreviations and Codes

Weather Phenomena

Qualifiers

Cloud Cover

Step-by-Step METAR Decoding Example

Example METAR

METAR KLAX 221530Z 27010KT 10SM FEW020 SCT100 18/10 A3012 RMK AO2 SLP200

Plain English Summary:
At Los Angeles International Airport, on the 22nd day at 15:30 UTC, wind is from the west at 10 knots, visibility is 10 miles, a few clouds at 2,000 ft and scattered at 10,000 ft, temperature is 18°C, dew point 10°C, altimeter is set to 30.12 inHg. The station is automated with a precipitation discriminator, sea-level pressure is 1020.0 hPa.

Real-World Applications

• Flight Planning: Ensures route, alternates, and approach procedures are suitable for current weather.
• Safety: Immediate updates (SPECI) alert crews and controllers to sudden hazards like wind shear, fog, or thunderstorms.
• Regulatory Compliance: Required for legal flight under VFR/IFR minima.
• Meteorological Analysis: Densely sampled, real-time data benefits weather modeling and climatology.

Summary

A METAR is the backbone of operational aviation weather, providing globally standardized, real-time observations essential for flight safety, air traffic management, meteorology, and drone operations. Mastery of METAR decoding ensures informed, safe, and compliant operations in the dynamic environment of flight.

For more information about METARs and how they integrate into modern aviation and weather systems, contact our team or schedule a demo to see powerful METAR decoding in action.