Meteorology
The atmosphere and stability
Know the ISA: sea-level temperature 15 °C, pressure 1013.25 hPa, lapse rate 1.98 °C per 1,000 ft, and the tropopause. Stability depends on the environmental lapse rate compared with the dry and saturated adiabatic rates; stable air gives stratiform cloud and steady precipitation, unstable air gives cumuliform cloud, showers and turbulence. Understand lapse rates, inversions, fog types, and the formation of radiation, advection and frontal fog.
Weather hazards and altimetry
Know icing types (rime, clear, mixed), the conditions for airframe icing, thunderstorms and their hazards (downbursts, hail, lightning, wind shear, microbursts), mountain waves, jet streams, sea breezes, and tropical revolving storms. Altimetry traps are common: QNH gives elevation, QFE gives height above the aerodrome, standard 1013.2 is used above the transition level; flying from high to low pressure or high to low temperature makes the true altitude lower than indicated.
Worked example
Surface temperature 20 °C, dew point 8 °C. Spread = 12 °C. Convective cloud base ≈ 400 × 12 = 4,800 ft AGL. If terrain rises to 4,000 ft, the cloud base is only 800 ft above the terrain - a useful cross-check on a METAR or TAF.
Rule of thumb
Cloud base (ft) ≈ 400 × (temperature − dew point) in °C; “high to low, look out below” for pressure and temperature.