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| Nimbostratus cloud | |
 Nimbostratus has very few visual features. |
|
| Abbreviation | Ns |
|---|---|
| Symbol |  |
| Genus | Nimbo- (rain) -stratus (layered) |
| Species | cloud |
| Variety | cloudy |
| Altitude | below 2,400 m (below 8,000 ft) |
| Classification | Family C (Low-level) |
| Appearance | Dark, Widespread, formless layer |
| Precipitation cloud? | Yes, but may be virga |
A Nimbostratus cloud is characterized by a formless cloud layer that is almost uniformly dark gray. It is a stratiform cloud that produces rain, developing cloud bases between the surface and 10000 ft (3000 m), as defined by the WMO. The cloud base is usually develops above 6500 ft (2000 m). Nimbo is from the Latin word "nimbus" meaning rain. Nimbostratus block a great amount of sunlight as a result of its characteristic dense structure. Nimbostratus usually has a thickness of 6,500-10,000 ft (2,000-3,000 meters), but can vary from 3,500 ft (1,000 m) to 15,000 ft (4,500 m) in thickness. In rare cases, nimbostratus can be very thin and accompanied by a separate layer of altostratus divided by a cloudless layer.
The base of a nimbostratus base cloud is dimmed by precipitation and is usually not clearly visible. In all cases, nimbostratus is accompanied by pannis 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, stratus, altostratus and stratocumulus clouds all have a smooth gray appearance. Usually, nimbostratus is a sign of steady moderate to heavy precipitation. However, precipitation does not occur at ground level in case of virga and accompanies other cloud types. There are a number of features allowing the observer to distinguish nimbostratus from other clouds:
- Stratus clouds bring much lighter precipitation (drizzle) than nimbostratus;
- Altostratus clouds are lighter in color and less opaque than nimbostratus, so sunlight can be seen through them;
- Cirrostratus clouds never bring precipitation and have a thin, whitish, veil-like structure, characteristic for cirrus;
- Stratocumulus bring only light precipitation and have clearly visible base with easily 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 lighter, constant precipitation.
Other typical precipitation-bearing clouds are cumulonimbus.
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Wikipedia content modification information:
- This page was last modified on 3 November 2008, at 16:36.
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