what is a cumulonimbus cloud?
Cumulonimbus clouds. Credit: NASA. Cumulonimbus clouds are a type of cumulus cloud associated with thunder storms and heavy precipitation. They are also a variation of nimbus or precipitation bearing clouds.They are formed beneath 20,000 ft. and are relatively close to the ground.umulonimbus clouds form in the lower part of the troposphere, the layer of the atmosphere closest to the surface of the Earth. This region due to evaporation and the greenhouse effect produces alot of the warm updrafts that make creation of cumulus and cumulonimbus clouds possible.