What type of cloud causes thunderstorms?
Quick answer
Thunderstorms come from cumulonimbus clouds: huge, towering clouds that can reach 12–18 km (7–11 miles) high. They produce lightning, thunder, heavy rain, hail and sometimes tornadoes. Their flat, spreading tops are called anvils because of their shape.
The name comes from Latin: cumulus means “heap” and nimbus means “rain cloud.” A cumulonimbus is literally a heaped-up rain cloud.
How a thunderstorm cloud forms
- Warm, moist air rises, often on hot afternoons.
- As it rises, it cools, and water vapor condenses into a puffy cumulus cloud.
- If the air keeps rising strongly, the cloud grows taller and taller.
- Near the top, it hits the stratosphere, where it can’t rise further, so it spreads out into a flat anvil.
- Ice and water particles collide inside, building up electric charge that releases as lightning.
The 10 main cloud types
| Height | Cloud types |
|---|---|
| High (above ~6 km) | Cirrus, cirrocumulus, cirrostratus |
| Middle (2–6 km) | Altocumulus, altostratus |
| Low (below 2 km) | Stratus, stratocumulus, nimbostratus |
| Vertical (spanning levels) | Cumulus, cumulonimbus |
Thunderstorm safety
- If you can hear thunder, you’re close enough to be struck by lightning.
- Go indoors or into a hard-topped car.
- Avoid open fields, hilltops, tall isolated trees and water.
- Wait about 30 minutes after the last thunder before going back outside.
Counting the distance
Light travels almost instantly, but sound travels about 1 km every 3 seconds (1 mile every 5 seconds). Count the seconds between a flash and its thunder to estimate how far away the storm is.
The strongest cumulonimbus storms can spawn tornadoes; see what the Fujita scale measures. For the layer the anvil hits, see which layer contains the ozone layer.
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