Nimbostratus cloud

Nimbostratus cloud
Nimbostratus with fractus
Abbreviation	Ns
Symbol
Genus	Nimbostratus (rain, layered)
Species	Stratiformis
Altitude	below 3,000 m (below 10,000 ft)
Classification	Family D (Vertically developed)
Appearance	Dark, widespread, formless layer
Precipitation cloud?	Yes, but may be virga
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A Nimbostratus cloud is characterized by a formless cloud layer that is almost uniformly dark gray. "Nimbo" is from the Latin word "nimbus", which denotes precipitation. It is generally a stratiform cloud of moderate vertical development (family D1) that produces precipitation, developing cloud bases between the surface and about 10000 ft (3000 m). This cloud typically forms from altostratus in the middle altitude range then subsides into the low altitude range during precipitation.^[1] Nimbostratus usually has a thickness of about 2000 meters. Though found worldwide, nimbostratus is found more commonly in the middle latitudes.^[2]

Appearance

The base of a nimbostratus base cloud is dimmed by precipitation and is usually not clearly visible. In all cases, nimbostratus is accompanied by pannus clouds, which develop underneath of nimbostratus. If the pannus layer is completely opaque, the presence of precipitation indicates presence of nimbostratus. The pannus movement is slow and uniform under nimbostratus.

Distinguishing features

Nimbostratus, stratus, altostratus and stratocumulus clouds all have a smooth gray appearance. There are a number of features allowing an 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 of cirrus;
• Stratocumulus bring only light precipitation and have clearly visible base with easily distinguished separate cloud elements;
• Large and low cumulonimbus clouds covering most of the sky can be mistaken for nimbostratus. However, they bring heavier, less constant precipitation.

Formation

Nimbostratus will occur along warm fronts where the slowly rising warm air mass creates nimbostratus and stratus clouds, which are preceded by higher-level clouds such as cirrostratus and altostratus.^[3][4] Often, when an altostratus cloud thickens and descends into lower altitudes, it will become nimbostratus.^[5]

Forecast

Nimbostrati often have very few visual features.

Usually, nimbostratus is a sign of steady moderate to heavy precipitation, as opposed to the shorter period of typically heavier precipitation released by a cumulonimbus cloud.^[2] However, precipitation does not occur at ground level in case of virga and accompanies other cloud types. Precipitation may last for several days, depending on the speed of the occluded front it accompanies.^[3] A nimbostratus virga cloud is the same as a normal nimbostratus, but the precipitation is virga and it never reaches the ground. Stratus or stratocumulus (comprising the warm sector of a frontal system) usually forms when it clears.

References

1. ^ World Meteorological Organization International Cloud Atlas
2. ^ ^{a b} Pretor-Pinney, Gavin (2007). The Cloudspotter's Guide: The Science, History, and Culture of Clouds. Perigee. ISBN 0399533451. http://books.google.com/books?id=MAiKY4xU6y8C. 
3. ^ ^{a b} Template:12345678910987654321 book
4. ^ Thompson, Graham; Turk, Jonathan (1993). Earth Science and the Environment. Fort Worth: Saunders College Publishing. ISBN 0030754461. 
5. ^ Lankford, Terry (2000). Aviation Weather Handbook. McGraw-Hill Professional. ISBN 9780071361033. http://books.google.com/books?id=kSSn7vPgmUQC&dq=nimbostratus+6500&cad=0. 

External links

• National Science Digital Library - Nimbostratus
• Nimbostratus and Other Low Clouds