Stratus cloud
Stratus opacus uniformis
Abbreviation	St
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.
This box: view • talk •

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, 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 fog that is above ground level and are formed either through the lifting of morning fog or when cold air moves at low altitudes over a region. These clouds do not usually bring precipitation, although drizzle may occur.

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 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

This climatology/meteorology-related article is a stub. You can help Wikipedia by expanding it.