Cumulonimbus Clouds and Thunderstorms: How Pilots Avoid Them
Cumulonimbus (CB) clouds carry hail, severe turbulence, and lightning. Here's how pilots detect and route around them — and why your flight might suddenly turn.
What's in a CB
A mature cumulonimbus contains:
- Updrafts and downdrafts up to 60 m/s.
- Hail (sometimes large enough to damage radomes).
- Lightning (mostly absorbed by the airframe but startling).
- Severe turbulence.
Why pilots avoid them
The standard rule is 20 nautical miles from any visible CB cell. Penetrating one risks structural damage and severe injuries to unbelted passengers.
How they detect them
- Onboard weather radar in the nose paints precipitation reflectivity.
- Lightning detection systems (StormScope/StrikeFinder) supplement.
- Datalink uplinks (e.g., WSI InFlight) bring NEXRAD-like images into cockpit displays.
- Visual scan in daytime VMC.
What you'll feel
Routes will appear circuitous. The captain may request altitude changes. Bumps near a deviation are common but not dangerous.
What FlightyFlow shows
NEXRAD overlay on the live track. When you see a sudden 30° course change with red blobs nearby, you're watching the radar do its job.
Frequently asked
Why does my flight detour around a thunderstorm?+
Pilots must stay 20 nm from cumulonimbus cells. Onboard weather radar paints those cells, and ATC supports the deviations.
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