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.

These clouds are commonly associated with severe weather, including heavy rain, downbursts, and occasionally a tornado.

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

If the correct atmospheric conditions are met, they can grow into a supercell storm.

They are capable of producing severe storm conditions for a short amount of time.