Thunderstorms, Turbulence, Icing, and Other Aviation Hazards
What to know
Know thunderstorm types (single cell, multicell, supercell, squall line), the three required ingredients (moisture, instability, lifting mechanism), and the life cycle (cumulus, mature, dissipating). The mature stage brings the greatest hazards: severe turbulence, hail, lightning, microbursts, and wind shear. Know the difference between a microburst and a downburst, and how gust fronts form.
For turbulence, distinguish mechanical, thermal, frontal, and clear-air turbulence (CAT), the latter associated with jet streams and strong wind shear. For icing, know the types (rime, clear, mixed), the temperature range (roughly 0 to −20 °C, with clear icing most likely near 0 to −10 °C in large supercooled droplets), and that freezing rain is the most dangerous. Recognise other hazards: mountain waves, volcanic ash, and low-level wind shear.
Traps
Questions often assume all icing occurs below freezing at the surface, or that hail requires a surface temperature above 0 °C. Another trap is confusing CAT with mountain wave turbulence.
Rule of thumb
Avoid Cb by at least 20 nm, and never attempt to fly beneath a thunderstorm. If freezing rain is forecast, treat it as a no-go for icing.