Clouds and what they tell a pilot
Recognizing cloud types — cumulus, stratus, and the dangerous cumulonimbus — and the conditions they signal.
Clouds are visible clues to what the atmosphere is doing. For pilots, three families matter most.
- Stratus — flat, layered, "stratified" clouds that form in stable air. They bring smooth flying but low ceilings, reduced visibility, drizzle and fog. A stratus deck under an inversion is the classic IFR/MVFR maker. Stable air also traps haze.
- Cumulus — puffy, "heaped" clouds that form in unstable air as warm parcels rise. Fair-weather cumulus mean bumps and good visibility; growing towering cumulus signal strong convection and turbulence.
- Cumulonimbus (CB) — the thunderstorm cloud, and the one to avoid by miles. A mature CB packs severe turbulence, severe icing, lightning, hail, microbursts and wind shear. The standard guidance is to stay at least 20 nautical miles from a thunderstorm and never to fly under, into, or between cells.
The prefix and suffix add detail: nimbo-/-nimbus means rain-bearing; alto- means mid-level; cirro-/cirrus means high, icy, wispy clouds (often the first hint of an approaching warm front).
The practical reading: layered = stable = smooth but low and wet; puffy = unstable = bumpy but clearer; anvil-topped = danger. Combine what you see out the window with the METAR/TAF and radar. When cumulus start building vertically on a humid afternoon, expect the ride to deteriorate and convective weather to develop.
*Reference and training only. Use official briefings for flight planning.*