Cumulonimbus clouds

The "King" of the clouds, cumulonimbus clouds are dense tall clouds. Cumulonimbus is responsible for lightning, thunder and hail. The underside of the cloud plume is often flat and can be just hundreds of feet from the earth's surface.

Characteristics.

Towering, menacing. The top is puffy and the cloud is thick and has a steep overhanging wall effect.

What's in a name?

Cumulus - heaped. Nimbus - rain/dark cloud.

How was it made?

From the smaller cumulus clouds when they travel over warmer surfaces. The cloud needs both moisture and warmth to force the cloud to grow and develop. As the cloud grows lots of energy is stored in this type of cloud as it piles height. If it's forming on a cold front it can be made by the forced warmer air being pushed up on top of the colder air underneath.

What weather will you have if these are overhead?

Extreme weather could be in store. They are the clouds associated with rain, hail, snow, lightning and thunderstorms as well as tornadoes.

How high is it?

The base is anywhere from 300 m (1,000ft) at the base although this can form up to 2,000m (6,500 ft)
The top can reach 15,000 - 18,000 m (45,000 - 52,000 ft)

Outcome for you.

Time to seek shelter or make sure you have your raincoat with you. If the hint of a lightning storm then finding a good vantage point to watch is important