Meteorological Terminal Air Report

What is METAR?

A METAR is a coded weather observation report generated at an airport, typically issued every 30 minutes or every hour depending on the country. The format is standardized by ICAO and the World Meteorological Organization (WMO), making it universally readable regardless of the issuing country's language. Every METAR follows the same sequence: station identifier, date/time (UTC), wind direction and speed, visibility, present weather phenomena, cloud cover and heights, temperature, dewpoint, altimeter setting (QNH), and optional remarks.

A typical METAR might read: EGLL 150950Z 24015G25KT 9999 FEW040 SCT100 18/09 Q1013. Decoded, this tells us Heathrow (EGLL) at 0950 UTC on the 15th: wind from 240 degrees at 15 knots gusting to 25, visibility greater than 10 km, few clouds at 4000 feet, scattered at 10,000 feet, temperature 18C, dewpoint 9C, QNH 1013 hPa. Pilots, dispatchers, and meteorologists worldwide read this format fluently.

When weather changes significantly between scheduled observations, a special report called SPECI is issued using the same format. SPECI reports are triggered by specific thresholds: sudden wind shifts, visibility drops below minima, onset of thunderstorms, formation or dissipation of fog, or any condition that crosses a defined operational threshold. Together, regular METARs and SPECI reports provide a continuous picture of airport weather conditions.

Why It Matters for Airspace Risk

METARs are a primary data source for detecting conditions that affect airspace safety beyond routine weather. The present weather group in a METAR can encode volcanic ash (VA), sandstorms (SS), dust storms (DS), and other phenomena that constrain or close airspace. During volcanic eruptions, METARs from airports in the ash fallout zone may be the first systematic reports of ash presence at ground level, complementing SIGMET and VAAC advisories that cover upper airspace.

For airspace risk assessment, METAR data provides ground-truth verification of conditions that affect operational decisions. When an airport is surrounded by conflict, meteorological services may be degraded or unavailable, and the absence of METAR reports is itself a risk indicator. If a major airport stops issuing METARs, it often means the aerodrome has ceased or severely reduced operations — a signal that is detectable before formal NOTAM closure announcements. Monitoring METAR availability across a region thus provides early warning of infrastructure disruption.

Key Facts

• •METARs are issued every 30-60 minutes at airports worldwide, using a standardized ICAO/WMO format.
• •SPECI reports are issued between regular METARs when conditions change significantly (wind shift, visibility drop, thunderstorm onset).
• •The format encodes wind, visibility, weather, clouds, temperature, dewpoint, and pressure in a compact text string.
• •Automated weather stations (AWOS/ASOS) generate METARs at airports without dedicated human observers.
• •Absence of METAR reports from a normally active airport can indicate infrastructure disruption or operational closure.

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