How to Read an Aviation Routine Weather Report (METAR)

by
Spread the love

How to Read an Aviation Routine Weather Report (METAR)

A METAR (Meteorological Aerodrome Report) is a standardized aviation weather observation report that provides essential information on the current weather conditions at an airport or aerodrome. METARs are issued on a regular basis, typically every hour, and are used by pilots, air traffic controllers, and meteorologists to assess the weather for safe flight planning and operations.

Understanding the METAR Format

A typical METAR consists of a series of standardized codes that convey weather data such as wind, visibility, temperature, dew point, atmospheric pressure, and other relevant meteorological information. These codes follow a specific format to ensure consistency and clarity. Here is a breakdown of the key elements you will encounter in a METAR:

1. METAR Identifier

  • Format: METAR or SPECI
  • METAR indicates a routine, scheduled report.
  • SPECI is a special report issued when there is a significant change in weather conditions between routine reports.

2. Station Identifier

  • Format: Four-letter ICAO code (e.g., KJFK, EGLL).
  • Represents the airport or weather station where the observation is made.
  • The first letter usually represents the country or region (e.g., K for the U.S., E for the U.K.).

3. Date and Time of Report

  • Format: DDHHMMZ
  • DD is the day of the month.
  • HHMM is the time in UTC (Coordinated Universal Time).
  • Z denotes Zulu time (UTC).

Example: 151230Z means the report was issued on the 15th day of the month at 12:30 UTC.

4. Wind Information

  • Format: DDDSSKT or DDDSSGSSKT
  • DDD is the wind direction in degrees true (from which the wind is blowing).
  • SS is the wind speed in knots.
  • GSS (optional) indicates gusts, with SS representing the maximum gust speed.
  • KT denotes knots as the unit of speed.

Example: 36012KT indicates wind from the north (360 degrees) at 12 knots. 18015G25KT indicates wind from the south (180 degrees) at 15 knots, gusting to 25 knots.

5. Visibility

  • Format: VVVV or VVVSM
  • VVVV is visibility in meters for countries using the metric system.
  • VVVSM is visibility in statute miles (SM) for countries like the U.S.
  • 9999 indicates visibility is 10 kilometers or more.
  • 0000 indicates visibility is less than 50 meters.

Example: 10SM indicates visibility is 10 statute miles. 6000 indicates visibility is 6,000 meters.

6. Runway Visual Range (RVR)

  • Format: RDRD/VVVVFT or RDRD/VVVV
  • RDRD is the runway designator.
  • VVVV is the visual range in feet or meters.
  • Indicates visibility along a specific runway.

Example: R27L/1800FT means runway 27 left has a visual range of 1,800 feet.

7. Weather Phenomena

  • Format: Two-character codes.
  • Describes significant weather events such as rain, snow, fog, etc.
  • Symbols preceding the codes provide additional details:
    • - Light intensity (e.g., -RA for light rain).
    • No symbol for moderate intensity.
    • + Heavy intensity (e.g., +SN for heavy snow).
    • VC Vicinity (within 5-10 miles, e.g., VCTS for thunderstorms in the vicinity).

Common Codes:

  • RA = Rain
  • SN = Snow
  • TS = Thunderstorm
  • BR = Mist
  • FG = Fog
  • DZ = Drizzle

Example: +TSRA indicates a thunderstorm with heavy rain.

8. Sky Condition

  • Format: Series of codes describing the cloud cover.
  • CLR or SKC = Clear skies (no significant clouds below 12,000 feet AGL).
  • FEW = Few clouds (1-2 oktas or eighths of sky coverage).
  • SCT = Scattered clouds (3-4 oktas).
  • BKN = Broken clouds (5-7 oktas).
  • OVC = Overcast (8 oktas, full sky coverage).
  • VV = Vertical visibility (used when obscuration such as fog is present).
  • Each code is followed by a three-digit number indicating the altitude of the cloud base in hundreds of feet AGL (above ground level).

Example: BKN025 means broken clouds at 2,500 feet. OVC007 indicates an overcast sky at 700 feet.

9. Temperature and Dew Point

  • Format: TT/DD
  • TT is the air temperature in degrees Celsius.
  • DD is the dew point temperature in degrees Celsius.
  • A preceding M (minus) indicates a negative temperature.

Example: 18/14 means the air temperature is 18°C and the dew point is 14°C. M02/M05 indicates a temperature of -2°C and a dew point of -5°C.

10. Altimeter Setting (Pressure)

  • Format: APPPP
  • A stands for altimeter setting.
  • PPPP is the pressure in inches of mercury for the U.S. (e.g., A2992 for 29.92 inches).
  • Outside the U.S., Q is used with the pressure in hectopascals (e.g., Q1013 for 1013 hPa).

11. Remarks (RMK)

  • Format: RMK followed by additional data.
  • Provides extra details not covered in the standard report, such as runway conditions, specific weather events, or equipment failures.
  • Can include information on lightning (e.g., OCNL LTG for occasional lightning) or recent weather changes (RE).

Example: RMK AO2 SLP134 means the report was made by an automated weather station with a precipitation sensor (AO2), and the sea-level pressure is 1013.4 hPa.

Sample METAR Report and Breakdown

Let’s decode a sample METAR:

METAR KJFK 151230Z 30012G18KT 10SM FEW050 SCT100 BKN250 22/16 A3015 RMK AO2 SLP210
  • METAR: Routine weather report.
  • KJFK: John F. Kennedy International Airport.
  • 151230Z: Report issued on the 15th day at 12:30 UTC.
  • 30012G18KT: Wind is from 300° at 12 knots, gusting to 18 knots.
  • 10SM: Visibility is 10 statute miles.
  • FEW050: Few clouds at 5,000 feet AGL.
  • SCT100: Scattered clouds at 10,000 feet AGL.
  • BKN250: Broken clouds at 25,000 feet AGL.
  • 22/16: Temperature is 22°C, dew point is 16°C.
  • A3015: Altimeter setting is 30.15 inches of mercury.
  • RMK AO2 SLP210: Automated station with a precipitation sensor; sea-level pressure is 1021.0 hPa.

Conclusion

Reading a METAR requires understanding the structured format and interpreting various abbreviations and codes. It’s a critical skill for aviation professionals and enthusiasts, ensuring safe and effective flight planning. With practice, you can quickly decipher these reports and gain insight into current weather conditions at an aerodrome.