Meteorology
Meteorology tests the weather knowledge needed for VFR decision-making in Namibia: pressure and altimetry, cloud, wind, thunderstorms, icing and local effects.
Pressure and altimetry
QNH is the altimeter setting that reads elevation on the ground; QFE reads height above the aerodrome; QNE is 1013.25 hPa at the transition. Flying from high to low pressure without adjusting the subscale makes the altimeter over-read and the aircraft lower than indicated.
Cloud and stability
A stable layer gives stratiform cloud and drizzle; unstable air gives cumulus and showers. The convective cloud base is roughly 400 ft per °C of surface temperature–dewpoint spread. A spread of 10°C gives about 4,000 ft AGL.
Wind, fronts and local effects
Sea breeze, anabatic/katabatic flow, mountain wave and dust devils are common in Namibia. Coastal fog forms with cool maritime air; east winds can bring hot, dry, turbulent conditions. Avoid cumulonimbus: hail, icing, wind shear and microbursts.
Worked example
Surface temperature 28°C, dewpoint 16°C. Spread = 12°C. Estimated convective cloud base = 12 × 400 = 4,800 ft AGL. If the terrain is 5,000 ft AMSL, the cloud base is about 9,800 ft AMSL; the 4,800 ft is AGL, not AMSL.
Traps
Confusing QNH and QFE; applying the 400 ft rule to stratiform cloud; forgetting temperature correction when flying in cold air; treating a high cloud base as 'no convective risk'; flying into a dust storm.