Anvil (meteorology)
Cumulonimbus with a large anvil
In meteorology , the upper part of a cumulonimbus cloud is called an anvil .
It arises when, compared to the environment, air parcels that are warmer and therefore lighter rise until they reach the level of thermal equilibrium, the tropopause . No further ascent is possible there. Since more light air flows in, the air has to spread sideways (mostly following the high-altitude winds in one direction). This creates the cloud shape that is reminiscent of an anvil.
In connection with "anvil clouds" (cumulonimbus), thunderstorms almost always occur .