Clouds, Precipitation and Their Aviation Significance
What the exam tests
This domain tests cloud identification, precipitation types and the operational significance of cloud and precipitation.
Core rules
- Stratiform cloud (stratus, altostratus, nimbostratus) suggests stable air, widespread cloud and steady precipitation; cumuliform cloud (cumulus, cumulonimbus) suggests instability, showers and turbulence.
- Cumulonimbus is the main convective hazard: lightning, hail, severe turbulence, icing, microbursts and heavy rain. An anvil and a dark, sloping base are warning signs.
- Ceiling is the lowest broken or overcast layer, not the lowest scattered layer. Cloud base in METAR/TAF is height above aerodrome elevation, not AMSL.
- Precipitation can evaporate before reaching the ground (virga), so a cloud may look threatening while the surface remains dry.
Worked example
A cumulus field builds vertically through the afternoon, tops reach 20,000 ft and an anvil spreads downwind. The reasoning is: deep vertical development plus an anvil indicates a cumulonimbus, so expect icing above the freezing level, hail and strong gusty winds. Plan a track that avoids the cell and its downwind anvil, not just the visible base.
Traps
Calling any dark cloud a ceiling; reading cloud heights as AMSL; assuming rain is reaching the ground; underestimating hail and turbulence under an anvil.