A METAR (Meteorological Aerodrome Report) is a standardized weather observation issued for a specific airport, reporting current atmospheric conditions in a coded format that pilots and dispatchers decode before every flight.
How It Works#
Airports issue METARs on a fixed schedule, typically every 30 minutes for most stations and every 20 minutes at busier aerodromes. Automated systems (called ASOS or AWOS) collect the raw data, while human observers at some stations can add remarks or correct automated readings.
Each METAR follows a strict, internationally standardized format governed by ICAO Annex 3. The report includes the station identifier, observation time (in UTC), wind direction and speed, visibility, present weather, sky condition, temperature and dew point, and altimeter setting. Pilots read these elements in order, left to right, every time.
The temperature and dew point are reported in degrees Celsius. The altimeter setting appears in inches of mercury (inHg) in the United States, or hectopascals (hPa) in ICAO-standard countries. Pilots plug these values directly into performance calculations, most critically density altitude.
A special type of METAR called a SPECI is issued outside the regular schedule whenever conditions change rapidly. A sudden drop in visibility, a wind shift, or the appearance of thunderstorms will all trigger a SPECI.
Example in Aviation#
A pilot preparing for a departure from Denver International Airport (KDEN) pulls up the latest METAR: KDEN 151753Z 18012KT 10SM CLR 32/08 A2992 RMK AO2. She reads a surface wind from 180 degrees at 12 knots, 10 statute miles visibility, clear skies, a temperature of 32°C, dew point of 8°C, and an altimeter setting of 29.92 inHg.
With a temperature of 32°C at Denver's field elevation of roughly 5,430 feet MSL, she calculates a density altitude well above 8,000 feet. She adjusts her takeoff roll and climb performance figures accordingly. Without the METAR, she would be guessing.
Why It Matters#
METARs are the primary source of current airport weather for flight planning and go/no-go decisions. A pilot who misreads or ignores a METAR risks launching into conditions that exceed the aircraft's limits or the pilot's own currency requirements.
Beyond weather awareness, the data inside a METAR feeds directly into critical performance calculations. Temperature and pressure altitude combine to determine density altitude, which governs how much runway the aircraft needs and how well it will climb. Getting these numbers right is not optional.
Key Takeaways#
- METARs follow a fixed ICAO format, issued every 30 minutes at most airports.
- Key elements include wind, visibility, sky condition, temperature, dew point, and altimeter setting.
- A SPECI is an unscheduled METAR triggered by rapidly changing conditions.
- Temperature and altimeter data from a METAR feed directly into density altitude calculations.
- Always decode the full METAR report, not just a single element, before flight.