Decoding a METAR

A METAR reports the weather observed at an airport right now. It lists the same fields in the same order: station · day/time · wind · visibility · sky · temperature/dew point · altimeter. Nothing is labelled, so you read each field by its position.

• Wind 24015KT means from 240° TRUE at 15 kt. A G marks a gust (24015G25KT); VRB means variable, and 00000KT means calm. METAR wind is always true; ATC (the tower) passes the surface wind in magnetic (RAC 4.2.5) to match runways numbered by magnetic heading.
• Visibility 3SM is 3 statute miles, not kilometres and not nautical miles. Canadian and US METARs use SM; ICAO metric METARs abroad report visibility in metres (e.g. 9999) (ICAO Annex 3, not detailed in the TC AIM).
• Sky: each layer gives cover plus height in hundreds of feet. FEW/SCT (few and scattered) are not a ceiling; BKN/OVC (broken and overcast) are a ceiling. The ceiling is the lowest BKN or OVC layer, so it caps your usable height: BKN025 = 2,500 ft.
• Temperature/dew point M05/M12 is −5 °C / −12 °C. The M means minus; the code has no minus sign of its own.
• Altimeter A2992 is a setting of 29.92 inHg.

Trap: reading the wind as magnetic, taking visibility as km/nm, calling a scattered layer a ceiling, or dropping the M on a sub-zero temperature.

Practice