Слоистый дождевой облак (Sloisty dozhdevoy oblak)

Common type of rain cloud

A nimbostratus cloud is a multilevel, amorphous, nearly uniform, and often dark grey cloud that usually produces continuous rain, snow, or sleet, but no lightning or thunder. Although it is usually a low based cloud, it actually forms most commonly in the middle level of the troposphere and then spreads vertically into the low and high levels. Nimbostratus usually produces precipitation over a wide area. The prefix nimbo comes from the Latin word , which denotes "cloud" or "halo". Downward growing nimbostratus can have the same vertical extent as most large upward growing cumulus, but its horizontal expanse tends to be even greater.

Nimbostratus has a diffuse cloud base generally found anywhere from near surface in the low levels to about in the middle level of the troposphere. Although usually dark at its base, it often appears illuminated from within to a surface observer. Nimbostratus usually has a thickness of about Though found worldwide, nimbostratus occurs more commonly in the middle latitudes. Often, when an altostratus cloud thickens and descends into lower altitudes, it will become nimbostratus. Nimbostratus, unlike cumulonimbus, is not associated with thunderstorms, however at an unusually unstable warm front caused as a result of the advancing warm air being hot, humid and unstable, cumulonimbus clouds may be embedded within the usual nimbostratus. Lightning from an embedded cumulonimbus cloud may interact with the nimbostratus but only in the immediate area around it. In this situation with lightning and rain occurring it would be hard to tell which type of cloud was producing the rain from the ground, however cumulonimbus tend to produce larger droplets and more intense downpours. The occurrence of cumulonimbus and nimbostratus together is uncommon, and usually only nimbostratus is found at a warm front and sometimes in cold front.

Nimbostratus is generally a sign of an approaching warm or occluded front producing steady moderate precipitation, as opposed to the shorter period of typically heavier precipitation released by a cold frontal cumulonimbus cloud. Precipitation may last for several days, depending on the speed of the frontal system. Precipitation based supplementary features: Nimbostratus is a major precipitation cloud and produces the virga or precipitation features. The latter can achieve heavy intensity due to the cloud's vertical depth. Accessory cloud: Nimbostratus pannus is an accessory cloud of nimbostratus that forms as a ragged layer in precipitation below the main cloud deck. Pannus is coded CL7. Genitus mother clouds: This genus type can form from cumulus and cumulonimbus. Mutatus mother clouds: Nimbostratus can form due to the complete transformation of altocumulus, altostratus and stratocumulus.

Multi level nimbostratus is physically related to other stratiform genus types by way of being non convective in nature. However, the other sheet like clouds usually each occupy only one or two levels at the same time. Stratus clouds are low level and form from near ground level to at all latitudes. In the middle level are the altostratus clouds that form from to in polar areas, in temperate areas, and in tropical areas. Although altostratus forms mostly in the middle level of the troposphere, strong frontal lift can push it into the lower part of the high level. The main high level stratiform cloud is cirrostratus which is composed of ice crystals that often produce halo effects around the sun. Cirrostratus forms at altitudes of in high latitudes, in temperate latitudes, and in low, tropical latitudes. Of the non stratiform clouds, cumulonimbus and cumulus congestus are the most closely related to nimbostratus because of their vertical extent and ability to produce moderate to heavy precipitation. The remaining cumuliform (cumulus) and stratocumuliform (stratocumulus, altocumulus, and cirrocumulus) clouds have the least in common with nimbostratus.