Meteorology
Meteorology tests the pilot's ability to interpret weather information and anticipate hazards. It covers the standard atmosphere, pressure and temperature, stability, clouds, fronts, icing, turbulence, wind and the practical decoding of METAR, TAF and charts.
Atmosphere and stability
- ISA sea-level values are 15 C and 1013.25 hPa; the average lapse rate is about 2 C per 1,000 ft.
- Pressure altitude is the altitude indicated with 1013.25 hPa set; density altitude corrects pressure altitude for temperature. High temperature, high elevation and high humidity increase density altitude.
- Stable air tends to give stratiform cloud and steady precipitation; unstable air gives convective cloud, showers and turbulence.
- Fronts bring characteristic changes: a cold front has a steep slope, squally weather and a sharp wind shift; a warm front has a shallow slope and widespread cloud.
Hazards and reports
- Icing requires visible moisture and temperatures near or below freezing; airframe icing increases weight and drag and reduces lift.
- Wind shear and low-level turbulence are significant near fronts, hills and thunderstorms; avoid embedded thunderstorms.
- METAR reports observed conditions; TAF forecasts. Learn the groups: wind, visibility, cloud, temperature/dewpoint, QNH.
Worked example
Decode EGLL 121150Z 24012KT 9999 SCT025 18/12 Q1015. The report is for Heathrow, issued on the 12th at 11:50 UTC. Wind is 240 true at 12 kt; visibility is 10 km or more; cloud is scattered at 2,500 ft; temperature 18 C, dewpoint 12 C; QNH 1015 hPa. The spread of 6 C suggests a moderate risk of mist but not immediate fog.
Traps that cost marks
9999 means 10 km or more, not exactly 9 km. QFE is not QNH. A TAF validity group such as 1212/1312 defines the forecast period, not the issue time. Do not read a PROB30 group as a certainty. Dewpoint close to temperature indicates saturation and fog risk. Icing is not limited to visible precipitation.
Key points
- ISA: 15 C, 1013.25 hPa at sea level; lapse rate about 2 C per 1,000 ft.
- Density altitude rises with high temperature, elevation and humidity, degrading performance.
- Stable air gives stratiform cloud; unstable air gives convection and showers.
- Cold fronts bring sharp wind shifts and squally weather; warm fronts bring widespread cloud.
- METAR is observed weather; TAF is forecast; 9999 means 10 km or more.
- Icing needs visible moisture near freezing; it increases weight and drag and reduces lift.