Cumulonimbus calvus

Cumulonimbus calvus
Cumulonimbus calvus, with probable cumulonimbus incus in background
Abbreviation	Cb calv.
Symbol
Genus	Cumulonimbus (heap, cloud/severe rain)
Species	Calvus (bald)
Classification	Family D (Vertically developed)
Appearance	Tall clouds with puffy rounded tops
Precipitation cloud?	Yes

Cumulonimbus calvus is a moderately tall cumulonimbus cloud which is capable of precipitation, but has not yet reached the tropopause, which is the height of stratospheric stability where it forms into a cumulonimbus capillatus (fibrous-top) or cumulonimbus incus (anvil-top). Cumulonimbus calvus clouds develop from cumulus congestus, and its further development under auspicious conditions will result in cumulonimbus incus.

This cloud consists mainly of water droplets. By definition of cumulonimbus cloud, at its top water droplets are transformed into ice crystals, but for cumulonimbus calvus content of ice crystals is small and freezing is in early stage, so cloud top still looks round and puffy.

Cumulonimbus calvus is characterized by distinctive (between other types of cumulonimbus cloud) rounded shape and relatively sharp edges of its top area, unlike cumulonimbus incus or cumulonimbus capillatus, which have cirriform tops. Developing cumulonimbus calvus loses sharp outlines of the top as more water droplets transform into ice crystals. Strong updrafts may form pileus or thin vertical stripes protruding upwards out of the cloud. When upper part of the cloud freezes to greater extent and clearly visible cirriforms appears, cumulonimbus calvus turns into another species of cumulonimbus.

Cumulonimbus calvus arcus is a sub-type of cumulonimbus calvus, which has arcus cloud ahead of cloud's front.

Like other cumulonimbus clouds, cumulonimbus calvus can cause bad weather conditions including: