Description Nimbostratus and differences with similar clouds | Previous Top Next

Nimbostratus
Grey cloud layer, often dark, the appearance of which is rendered diffuse by more or less continuously falling Rain or Snow, which in most cases reaches the ground. It is thick enough throughout to blot out the sun. Low, ragged clouds frequently occur below the layer, with which they may or may not merge.
Main differences between Nimbostratus and similar clouds of other genera
(a) Altostratus
Thin Nimbostratus may be confused with thick Altostratus. Nimbostratus generally has a darker grey colour than Altostratus. By definition, Nimbostratus is sufficiently opaque throughout to hide the sun or moon, whereas Altostratus hides the luminary only when the latter is behind the thickest parts. If on dark nights, doubt exists regarding the choice of the designation Nimbostratus or Altostratus, the cloud is by convention called Nimbostratus when Rain or Snow reaches the ground.
(b) Altocumulus and Stratocumulus
Nimbostratus is distinguished from a thick layer of Altocumulus or Stratocumulus by the lack of clearly defined elements or its lack of a distinct lower surface.
(c) Stratus
Nimbostratus is distinguished from thick Stratus by the fact that it is a dense cloud producing rain, snow or ice pellets ; the precipitation which may fall from Stratus is in the form of Drizzle, Ice prisms or Snow grains.
(d) Cumulonimbus
When the observer is beneath a cloud having the appearance of a Nimbostratus, but accompanied by Lightning, Thunder or Hail, the cloud should by convention be called Cumulonimbus.