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 means that the thunderstorm is in its mature stage, succeeding the preceding cumulonimbus calvus stage. Cumulonimbus capillatus is a sub-form of cumulonimbus incus
This is a rare meteorological phenomenon called a ‘SKY PUNCH’. When people see these,they think it’s the end of the world. Ice crystals form above the high-altitude cirro-cumulo-stratus clouds,then fall downward, punching a hole in the cloudcover.
This towering cumulus cloud is a precursor of a cumulonimbus, or thunderstorm, cloud. These cauliflower-like clouds result from warm, moist air rising rapidly through a cooler layer. They typically have a horizontal base and a dome-shaped upper surface