Stratus cloud

Stratus cloud
Stratus opacus uniformis
Symbol
Genus	Stratus (layered)
Altitude	Below 2,000 m (Below 6,000 ft)
Classification	Family C (Low-level)
Appearance	horizontal layers
Precipitation cloud?	Yes, but usually minor precipitation
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A stratus cloud (St) is a cloud belonging to a class characterized by horizontal layering with a uniform base, as opposed to convective clouds that are as tall or taller than wide (these are termed cumulus clouds). More specifically, the term stratus is used to describe flat, hazy, featureless clouds of low altitude varying in color from dark gray to nearly white. A "cloudy day" usually features a sky filled with stratus clouds obscuring the disk of the sun. These clouds are essentially above-ground fog formed either through the lifting of morning fog or when cold air moves at low altitudes over a region.

Variations

Stratus formations that are accompanied by precipitation are known as nimbostratus. Stratus formations at higher altitudes include altostratus and cirrostratus. Cirrostratus clouds are sheet-like and composed of ice crystals. Though they can be several thousand feet thick and cover the entire sky, they are relatively transparent and the sun and moon are sometimes visible through them. One characteristic is that the sun and moon have a halo around them because of light refraction on the ice crystals.

View from below...

...level with...

...and above a layer of stratus cloud.

Wikimedia Commons has media related to: Stratus clouds

References

• Ackerman, Steven A. and John A. Knox, Meteorology: Understanding the Atmosphere. Brooks Cole, 2003.
• USA Today Weather site on stratus clouds
• Common cloud types
• Weather Wiz Kids
• http://www.ace.mmu.ac.uk/eae/weather/older/stratus_clouds.html

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