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 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.
Image:Sun shining through thick Stratus.jpg|View from below... Image:Stratus-Cloud-Uetliberg.jpg|...level with... Image:Nebelmeer-Uetliberg.jpg|...and above a layer of stratus cloud.
- 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
stratiform in Catalan: Stratus
stratiform in Czech: Stratus
stratiform in German: Stratus
stratiform in Estonian: Kihtpilv
stratiform in Modern Greek (1453-): Στρώματα
stratiform in Spanish: Stratus
stratiform in French: Stratus
stratiform in Galician: Stratus
stratiform in Korean: 층운
stratiform in Italian: Strato (meteorologia)
stratiform in Dutch: Stratus
stratiform in Japanese: 層雲
stratiform in Norwegian: Stratus
stratiform in Norwegian Nynorsk: Stratus
stratiform in Polish: Stratus
stratiform in Portuguese: Stratus
stratiform in Slovak: Stratus
stratiform in Slovenian: Stratus
stratiform in Finnish: Sumupilvi
stratiform in Swedish: Stratus (moln)
stratiform in Ukrainian: Шаруваті хмари
stratiform in Chinese: 层云