Weather Hazards to Aviation
This domain tests recognition and avoidance of icing, turbulence, thunderstorms and wind shear.
Icing
Rime ice forms in small-droplet stratiform cloud, clear or glaze ice in large supercooled droplets in stratiform and convective cloud, and mixed ice in between. The risk band is 0 to -20°C, greatest between 0 and -10°C; freezing rain is the most severe case. Carburettor icing can occur from about +5°C to +20°C with high relative humidity.
Turbulence
Mechanical turbulence is low-level over rough terrain with strong wind; convective turbulence comes with cumulus and cumulonimbus; clear air turbulence occurs near jet streams, especially at tropopause breaks and in anticyclonic shear zones.
Thunderstorms
Life cycle: cumulus stage with updraught only, mature stage with both updraught and downdraught plus lightning, hail, gust front and microburst, then dissipating stage. Hazards are severe turbulence, hail, icing, lightning, downbursts, wind shear and tornadoes.
Wind shear
A change of wind speed or direction with height or distance; low-level shear on approach is the most dangerous. A microburst is a small intense downdraught producing diverging surface winds.
Worked example
A cumulonimbus with a top at 40,000 ft and a weak echo region indicates a strong updraught, large hail and severe turbulence. Avoid it laterally by at least 20 km and do not overfly unless you can clear the top by at least 5,000 ft.
Traps
Treating clear ice and rime as the same hazard; dismissing carburettor icing at temperatures above 0°C; assuming turbulence occurs only inside cloud.