Stratus cloud
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| Abbreviation | St |
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| Symbol |  |
| Genus | Stratus (layered) |
| Altitude | Below 2,000 m (Below 6,000 ft) |
| Classification | Family C (Low-level) |
| Appearance | horizontal layers |
| Precipitation Cloud? | Yes |
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. 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 if sufficiently low in altitude to become fog, drizzle or mist may result.
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 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.
[edit] 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
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| High Clouds (Family A): | Cirrus (Ci) • Cirrus uncinus • Cirrus Kelvin-Helmholtz colombia • Cirrostratus (Cs) • Cirrocumulus (Cc) • Pileus • Contrail |
| Middle Clouds (Family B): | Altostratus (As) • Altostratus undulatus • Altocumulus (Ac) • Altocumulus undulatus • Altocumulus mackerel sky • Altocumulus castellanus cloud • Altocumulus lenticularis |
| Low Clouds (Family C): | Stratus (St) • Nimbostratus (Ns) • Cumulus humilis (Cu) • Cumulus mediocris (Cu) • Stratocumulus (Sc) |
| Vertical Clouds (Family D): | Cumulonimbus (Cb) • Cumulonimbus incus • Cumulonimbus calvus • Cumulonimbus with mammatus • Cumulus congestus • Pyrocumulus • Pyrocumulonimbus |
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