Cumulonimbus is a very tall, dense cloud type that contains rain and features lightning and thunder. While the cloud towers over the landscape it is considered part of the low family if its base in in the low levels. If the base is in the middle levels it is part of the middle cloud family. It is popularly known as a thunderstorm. Under the right conditions cumulonimbus are capable of producing severe weather such large hail, damaging winds, and tornadoes. Very heavy rain also can occur with thunderstorms. In dry climates thunderstorms often produce lightning and thunder with no or very little rain reaching the ground. 

Examples of the Cumulonimbus Principal Cloud Type