Description Cumulonimbus and differences with similar clouds | Previous Top Next

Cumulonimbus
Heavy and dense cloud, with a considerable vertical extent, in the form of a mountain or huge towers. At least part of its upper portion is usually smooth, or fibrous or striated, and nearly always flattened; this part often spreads out in the shape of an anvil or vast plume. Under the base of this cloud which is often very dark, there are frequently low ragged clouds either merged with it or not, and precipitation sometimes in the form of Virga.
Main differences between Cumulonimbus and similar clouds of other genera
(a) Nimbostratus
When Cumulonimbus covers a large expanse of the sky, it can easily be confused with Nimbostratus, especially when identification is based solely on the appearance of the under surface, In this case, the character of the precipitation may help to distinguish Cumulonimbus from Nimbostratus. If the precipitation is of the showery type, or if it is accompanied by Lightning, Thunder or Hail, the cloud is by convention Cumulonimbus.
(b) Cumulus
Certain Cumulonimbus clouds appear nearly identical with large, well-developed Cumulus. The cloud should be called Cumulonimbus as soon as at least a part of its upper portion loses the sharpness of its outlines or presents a fibrous or striated texture. If it is not possible to decide on the basis of the above criteria whether a cloud is a Cumulonimbus or Cumulus, it should by convention, be called Cumulonimbus if it is accompanied by Lightning, Thunder or Hail.