NIMBOSTRATUS CLOUD

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Nimbo is from the Latin word "nimbus" meaning rain. A 'Nimbostratus' is a cloud of the class characterized by a formless layer that is almost uniformly dark gray; it is a rain cloud of the layer type, of low altitude, usually below 8000 ft (2400 m) and sometimes down to 350 ft (100 m). Nimbostratus block a great amount of sunlight as a result of its characteristic dense structure. Thickness of nimbostratus layer is usually 6500..10000 ft (2000..3000 meters), but can reach up to 15000 ft (4500 m) and down to 3500 ft (1000 m). Nimbostratus in rare cases can be very thin and accompanied by separate layer of altostratus divided by cloudless layer.
The base of nimbostratus base cloud is dimmed by precipitation and usually isn't have clearly visible. In most cases, nimbostratus is accompanied by pannus clouds, which develop under layer of nimbostratus. If pannus layer is completely opaque, presence of precipitation indicates presence of nimbostratus. The pannus movement is slow and uniform under nimbostratus.
Nimbostratus clouds always bring either precipitation or virga. They often occur ahead of warm fronts, though also comprise the bulk of cloud mass in the "comma head" of precipitation N-NW of a cyclone, associated with heavy rain or snow. At front, the altidude of clouds is lowest.
There are variety of nimbostratus clouds, named according to cloud genera, which they have developed from.
Nimbostratus, stratus, altostratus and stratocumulus clouds all have a smooth gray appearance. Usually, steady moderate to heavy precipitation is clear sign of nimbostratus. However, precipitation does not occur at ground level in case of virga and accompanies other cloud types. There is number of features allowing to distinguish nimbostratus from other clouds:

★ Stratus clouds bring much lighter precipitation (drizzle) than nimbostratus;

★ Altostratus clouds are lighter in color and less opacue than nimbostratus, so sun can be seen through them;

★ Cirrostratus clouds never bring precipitation and have thin, whitish, veil-like structure, characteristic for cirrus;

★ Stratocumulus bring only light precipitation and have clearly visible base with easely distinguished separate cloud elements.
Moreover, large and low cumulonimbus cloud covering most of sky can be mistaken for nimbostratus. In this case, nimbostratus can be distinguished by absence of lightning and by lighter, constant precipitation.
Other typical precipitation-bearing clouds are cumulonimbus.

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External links

External links

★ National Science Digital Library - Nimbostratus

★ Nimbostratus and Other Low Clouds