Meteorological Observations, Reports, Forecasts and Charts (METAR, TAF, SIGMET, etc.)
Candidates must decode coded reports fluently. METAR is a routine aerodrome observation, usually issued hourly; SPECI is a special report issued when significant change occurs. TAF is an aerodrome forecast, short (9–12 h) or long (24–30 h). Trends, BECMG (gradual change), TEMPO (temporary fluctuations), and probability groups (PROB30, PROB40) are common traps.
Decoding essentials
Wind is given in degrees true and knots, with gusts after G and variability after V. Visibility is in metres (or statute miles in some states), with RVR given as R followed by the runway designator. Present weather uses two-letter codes (RA rain, SH shower, TS thunderstorm, FZ freezing, BR mist, FG fog). Cloud amount is FEW (1–2 oktas), SCT (3–4), BKN (5–7) and OVC (8), with height in hundreds of feet above aerodrome. Temperature and dew point are in whole degrees Celsius; QNH follows Q in hPa.
Other products
SIGMET warns of significant en-route weather (severe turbulence, icing, volcanic ash, tropical cyclones); AIRMET covers less severe phenomena for light aircraft. GAMET is an area forecast for low-level flights. Significant weather charts, wind and temperature charts and volcanic ash advisory charts complete the set.
Worked example: EGLL 121150Z 24015G28KT 9999 -RA BKN012 12/10 Q1008 means wind 240° true at 15 kt gusting 28, visibility 10 km or more, light rain, broken cloud at 1200 ft, temperature 12 °C, dew point 10 °C, QNH 1008 hPa.
Trap: BKN012 means cloud base at 1200 ft above aerodrome elevation, not above sea level.