Meteorology
Scope
Meteorology covers the atmosphere, altimetry, wind, clouds, fronts, icing, thunderstorms and weather reports. Expect questions that combine a report or forecast with a decision.
Core rules
- ISA: 15°C and 1013.25 hPa at MSL; lapse rate about 2°C per 1000 ft up to 36,090 ft.
- QNH gives altitude above MSL; QFE gives height above the aerodrome. 1 hPa is about 30 ft near sea level.
- “From high to low, look out below”: flying toward lower pressure without resetting the altimeter makes the true altitude lower than indicated. Cold air has the same effect.
- Cumuliform cloud base can be estimated from the temperature/dewpoint spread: about 400 ft per 1°C.
- Thunderstorms bring wind shear, microbursts, hail and icing; avoid them.
Worked example
Surface temperature 25°C, dewpoint 15°C, spread 10°C. Estimated convective cloud base ≈ 10 × 400 = 4000 ft AGL. Reasoning: the spread is the amount of cooling needed to reach saturation; the 400 ft/°C rule is an approximation for the lower troposphere. It does not apply to stratiform cloud.
Traps
Using QFE as QNH; applying the 400 ft/°C rule to frontal stratus; forgetting the temperature correction on a cold-day approach; reading a TAF as observed weather.