A cumulonimbus incus (from Latin incus 'anvil'), also called an anvil cloud, is a cumulonimbus cloud that has reached the level of stratospheric stability and has formed the characteristic flat, anvil-shaped top.^[1] It signifies a thunderstorm in its mature stage, succeeding the cumulonimbus calvus stage.^[2] Cumulonimbus incus is a subtype of cumulonimbus capillatus. These clouds are commonly associated with severe weather, including heavy rain, downbursts, and occasionally a tornado.

Quick Facts Abbreviation, Symbol ...

Cumulonimbus incus
A cumulonimbus incus cloud, showing the characteristic anvil-top shape the cloud type displays
Abbreviation	Cb inc.
Symbol
Genus	Cumulonimbus (heap, cloud/severe rain)
Species	Capillatus (Having hair)
Variety	None
Altitude	Ground to 23,000 m (75,000 ft)
Classification	Family C (Low-level)
Appearance	Large flat-top cloud
Precipitation	Very common rain, snow, snow pellets or hail, heavy at times

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A cumulonimbus incus is a mature thunderstorm cloud generating many dangerous elements.

• Lightning: this storm cloud is capable of producing bursts of cloud-to-ground lightning.
• Hail: hailstones may fall from this cloud if it is a highly unstable environment (which favours a more vigorous storm updraft).
• Heavy rain: this cloud may drop several inches (centimetres) of rain in a short amount of time. This can cause flash flooding.
• Strong wind: gale-force winds from a downburst may occur under this cloud.
• Tornadoes: in severe cases (most commonly with supercells), it can produce tornadoes. They are not directly produced by cumulonimbus incus but rather produced by supercells which come from cumulonimbus incus.

Cumulonimbus clouds can be powerful. If the correct atmospheric conditions are met, they can grow into a supercell storm. This cloud may be a single-cell thunderstorm or one cell in a multicellular thunderstorm. They are capable of producing severe storm conditions for a short amount of time.