Cumulonimbus incus
Abbreviation Cb inc
Family D
Genus Cumulonimbus
Occurrence Worldwide except Antarctica
Altitude 600-18000m
Formation powerful convection assisted by atmospheric instability
Precipitation Heavy rain or hail
Potential Hazards Severe turbulence, thunderstorms, hail, tornadoes, lightning, strong winds

Cumulonimbus incus (Cb inc; Latin for heap-raincloud anvil) is a typical cumulonimbus cloud which has expanded to the tropopause due to powerful updrafts and convection and which has fully developed an anvil shape. The tops of cumulonimbus incus clouds usually reach 10500m in altitude but may grow to 18000m, particularly near the equator; this is dependent upon the altitude of the tropopause at the location of cloud formation. As updrafts do not extend past the tropopause, the cloud is thrust upward until this point, where it is forced to spread radially into a characteristic "anvil" composed of ice crystals. Mammatus clouds may develop on the underside of this anvil. On rare occasions, part of the anvil may protrude into the stratosphere due to the updraft associated with anvil formation being more powerful than it is under normal circumstances. This is a warning sign which may herald the coming of a severe storm capable of producing tornadoes.

High Clouds (Family A): Cirrus (Ci) • Cirrus aviaticus • Cirrus intortus • Cirrus radiatus • Cirrus uncinus • Cirrus Kelvin-Helmholtz • Cirrostratus (Cs) • Cirrocumulus (Cc) • Pileus • Contrail
Middle Clouds (Family B): Altostratus (As) • Altostratus undulatus • Altocumulus (Ac) • Altocumulus undulatus • Altocumulus mackerel sky • Altocumulus castellanus • Altocumulus lenticularis
Low Clouds (Family C): Stratus (St) • Orographic stratus • Fog • Nimbostratus (Ns) • Cumulus humilis (Cu) • Cumulus mediocris (Cu) • Stratocumulus (Sc)
Vertical Clouds (Family D): Cumulonimbus (Cb) • Cumulonimbus incus • Cumulonimbus calvus • Cumulonimbus with mammatus • Cumulus congestus • Cumulus castellanus • Pyrocumulus  • Pyrocumulonimbus
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