Cumulonimbus calvus

Cumulonimbus Calvus is the first stage of Cumulonimbus, which is capable of producing precipitation, but not yet to the point of producing anvils. They grow from Cumulus congestus and consist mainly of water droplets. At this stage there are only upward drafts (ie hot air).

This type of Cumulonimbus has well-defined contours and a round shape like a cauliflower. One indicator of the evolution of Cumulus congestus to Cumulonimbus calvus is the pileus. When the top droplets begin to turn to ice, the cloud is in a state of transition to capillatus type.