Stratus cloud

Infobox Cloud
name = Stratus cloud
image location =Stratus-Opacus-Uniformis.jpg


abbreviation = St
symbol = CL_6.png genus= Stratus ("layered")
variety=
altitude_m = Below 2,000
altitude_ft = Below 6,000
level = low
appearance = horizontal layers
precipitation = Yes, but usually minor precipitation.

Stratus means layer or blanket in Latin. 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 above-ground fog 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 heavy precipitation, although drizzle and snow may occur.

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.

References

* Ackerman, Steven A. and John A. Knox, "Meteorology: Understanding the Atmosphere". Brooks Cole, 2003.
* [http://www.usatoday.com/weather/wstratus.htm USA Today Weather site on stratus clouds]
* [http://ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/cld/cldtyp/home.rxml Common cloud types]
* [http://www.weatherwizkids.com/cloud.htm Weather Wiz Kids]
*http://www.ace.mmu.ac.uk/eae/weather/older/stratus_clouds.html