Clouds and Precipitation
Classification
Clouds are grouped by height: high (cirrus, cirrostratus, cirrocumulus - ice), middle (altostratus, altocumulus - mixed), low (stratus, stratocumulus, nimbostratus - water), and vertical (cumulus, cumulonimbus - extend through levels).
Formation
Cloud forms when air cools to its dew point by lifting, radiative cooling, or mixing. Condensation nuclei are essential. Lifting mechanisms: convection, orographic lift, frontal lift, convergence.
Precipitation types
- Rain/drizzle: liquid; drizzle drops < 0.5 mm.
- Snow: ice crystals.
- Sleet: refrozen or partially melted.
- Hail: strong updrafts in cumulonimbus.
- Freezing rain: supercooled drops freezing on impact - severe icing hazard.
Worked example
A cumulonimbus with a strong updraft and high liquid water content produces hail and severe turbulence; avoid by at least 20 NM laterally and fly above the anvil. Nimbostratus gives steady, moderate rain and low ceilings - instrument approach weather.
Traps
Don't confuse altostratus (sun dimly visible) with cirrostratus (halo). Nimbostratus is not a thunderstorm cloud - that's cumulonimbus. Drizzle comes from stratiform cloud, not cumuliform.