Meteorology
Meteorology tests the atmosphere, pressure and altimetry, cloud and precipitation, icing, thunderstorms, and the tropical weather affecting East Africa.
Atmosphere and altimetry
- ISA: sea level 15°C, 1013.25 hPa, lapse rate 1.98°C per 1,000 ft to 36,090 ft.
- QNH sets aerodrome elevation; QFE sets height above aerodrome; standard pressure is used above transition altitude.
- Lows bring convergence and poor weather; highs bring subsidence and good weather.
Weather and hazards
- Cloud base: (T - Td) × 400 ft AGL. Adiabatic cooling and dew point explain saturation.
- Icing: clear ice in large supercooled droplets, rime in small droplets; use anti-ice or de-ice and avoid.
- Thunderstorms: cumulonimbus, gust fronts, microbursts, hail and lightning; avoid by at least 20 NM.
- Wind shear: sudden change in speed or direction; go around if the approach becomes unstable.
Kenya and tropical weather
- The ITCZ migrates seasonally; long rains occur March–May and short rains October–December. Easterly waves and tropical cyclones affect the coast.
- Sea breezes and anabatic/katabatic winds are common; high terrain causes orographic cloud.
Worked example
Surface temperature 24°C, dew point 16°C. Spread = 8°C. Estimated convective cloud base = 8 × 400 = 3,200 ft AGL. If terrain is 1,500 ft AMSL, cloud base is about 4,700 ft AMSL.
Traps
- Using QFE for terrain clearance.
- Assuming all icing is rime.
- Forgetting that the ITCZ moves seasonally.