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

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.

Cumulonimbus calvus with cloud-to-cloud lightning

Hazards

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

Lightning; these clouds produce lightning.
Wind; these clouds may produce strong winds especially during a downburst
Hail; these clouds can sometimes produce hail
More severe storms; The Cumulonimbus Calvus can further grow larger if the updraft is strong. it can form into a cumulonimbus incus, and bring more severe storms.

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Cloud genera and selected species, supplementary features, and other airborne hydrometeors - WMO Latin terminology except where indicated

Extreme-level	Polar mesospheric cirriform type Noctilucent

Very high-level	Polar stratospheric cirriform type Nacreous

High-level	Tropospheric cirriform, stratiform, and stratocumuliform genera Cirrus (Ci) Cirrostratus (Cs) Cirrocumulus (Cc) General type (non-WMO terminology) Aviaticus cloud (Contrail)

Medium-level	Tropospheric stratiform and stratocumuliform genera Altostratus (As) Altocumulus (Ac) Stratocumuliform species Altocumulus castellanus (Ac cas)

Low-level	Tropospheric stratiform, stratocumuliform and cumuliform genera Stratus (St) Stratocumulus (Sc) Cumulus (Cu) Stratiform and cumuliform species Fractus Cumulus humilis (Cu hum) Stratocumulus variants (non-WMO terminology) Actinoform cloud Asperitas

Moderate vertical	Tropospheric stratiform and cumuliform genera Nimbostratus (Ns) Cumulus (Cu) Cumuliform species Cumulus mediocris (Cu med) Cumuliform supplementary features Cumulus Pileus Cumulus Arcus (Roll)

Towering vertical	Tropospheric cumulonimbiform genus Cumulonimbus (Cb) Cumuliform species Cumulus congestus (ICAO term Towering cumulus [Tcu]) Cumuliform and cumulonimbiform supplementary features mamma Tuba (Funnel cloud) Pileus Arcus (Shelf) Cumuliform and cumulonimbiform variants (non-WMO terminology) Wall cloud Pyrocumulus Pyrocumulonimbus Cumulonimbuus Overshooting top Hot tower

Surface based	General type Fog

Non-height specific	General types Accessory cloud Kelvin–Helmholtz cloud

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