Cumulonimbus incus

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Cumulonimbus Incus
A Classic Anvil Cloud Over Europe.jpg
Cumulonimbus Incus
Abbreviation Cb inc.
Genus Cumulonimbus (heap, cloud/severe rain)
Species Capillatus (fibrous)
Classification Family D (Vertically developed)
Appearance Large flat-top cloud
Precipitation cloud? Yes, often intense

A cumulonimbus incus (Latin incus, "anvil") also known as an anvil cloud is a cumulonimbus cloud which has reached the level of stratospheric stability and has formed the characteristic flat, anvil-top shape. A cumulonimbus incus signifies the thunderstorm in its mature stage, succeeding the preceding cumulonimbus calvus stage. Cumulonimbus capillatus is a sub-form of cumulonimbus incus.


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's a highly unstable environment (which favors a more vigorous storm updraft).
  • Heavy rain; this cloud may drop several inches 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.


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.