Meteorology
Meteorology tests whether you can read the atmosphere well enough to predict what the aircraft will meet, and interpret the coded products (METAR, TAF, SIGMET) correctly.
Atmosphere and altimetry
ISA at sea level is 15°C and 1013.25 hPa, with a lapse rate of about 2°C per 1,000 ft up to the tropopause near 36,000 ft. Altimeter setting decides everything: QNH gives elevation above mean sea level, QFE gives height above the aerodrome, and standard 1013.25 hPa is used above the transition altitude. "High to low, look out below": flying from high pressure into low pressure without resetting makes the altimeter over-read, so the aircraft is lower than indicated. Cold air has the same effect; a rough allowance is 4% of the height per 10°C below ISA.
Pressure, wind and stability
Surface friction backs the wind and reduces its speed compared with the geostrophic flow aloft. Local effects matter in West Africa: the Harmattan is a dry, dust-laden northeasterly in December–February that cuts visibility and humidity; sea breezes reverse by night; stability determines whether cloud is stratiform (stable) or cumuliform (unstable). The saturated adiabatic lapse rate averages roughly 1.8°C per 1,000 ft.
Weather systems and hazards
Thunderstorms pass through cumulus, mature and dissipating stages; the mature stage brings hail, severe turbulence, microburst windshear and icing. Avoid cells by a wide margin, especially downwind. Icing is worst at 0°C to −15°C in visible moisture; clear ice is heavy and fast, rime is rough and blunt. Radiation fog forms on clear, calm nights; advection fog needs warm moist air over a cold surface.
Worked example
Surface temperature 24°C, dew point 15°C, spread 9°C. Using the 400 ft per °C rule of thumb, convective cloud base ≈ 9 × 400 = 3,600 ft AGL. Cross-check against the aerodrome forecast before planning a VFR transit.
Traps that cost marks
Confusing QFE and QNH; believing the altimeter shows true altitude; decoding 27015KT as wind blowing towards 270 (it blows from 270); treating a TAF as an observation; and confusing RVR with meteorological visibility.