Home » 1. Introduction to convective weather » Cumulonimbus (calvus, capillatus, incus) – thunderstorms Cumulonimbus (calvus, capillatus, incus) – thunderstorms


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Cumulonimbus capillatus incus (anvil-top) is a cumulonimbus cloud that has developed the characteristic flat, anvil-top form. An anvil top indicates a very strong updraft, the strongest among the Cumulonimbus species. Anvils usually top out at 10-12 km altitude, but they can reach as high as 16-18 km close to the equator.


  • Intense lightning.
  • Hail. Usually relatively small, 0.5 – 2 cm in diameter, but may become much bigger and damaging.
  • Heavy rainfall. Very heavy rainfall and or longer downpours can lead to flash flooding.
  • Strong wind. Strong straight line winds can occur. Under the right conditions they may exceed severe or even very severe criteria.
  • Waterspouts and landspouts. Less frequent than the above.
  • Tornadoes. Much less frequent than the above.