Cumulus cloud

Seeing a cumulus cloud means that the air is well mixed by up and down vertical drafts. When a cumulus cloud grows into a thunderstorm, the cloud is called a cumulonimbus cloud. This is a sign that the air is rising to the stratosphere.The Weather Book Wonders of Creation

References

Other websites

AMS Glossary of Meteorology
Cumulus cloud at BBC Weather 
Cumulus cloud page at University of Richmond internal site 
Time-lapse of the formation of Cumulus clouds 

Category:Clouds