page_title: Cirrus cloud
section_title: Thunderstorms
hierarchical_section_title: Cirrus cloud / Formation / Thunderstorms
context_page_description: Cirrus is a genus of atmospheric cloud generally characterized by thin, wispy strands, giving the type its name from the Latin word cirrus, meaning a ringlet or curling lock of hair. This cloud can form at any altitude between 5,000 and 13,700 m above sea level. The strands of cloud sometimes appear in tufts of a distinctive form referred to by the common name of "mares' tails".
  From the surface of Earth, cirrus typically appears white, or a light
  grey in color. It forms when water vapor undergoes deposition at altitudes above 5,500 m in temperate regions and above 6,400 m in tropical regions. It also forms from the outflow of tropical cyclones or the anvils of cumulonimbus clouds. Since cirrus clouds arrive in advance of the frontal system or tropical cyclone, it indicates that weather conditions may soon deteriorate. While it indicates the arrival of precipitation, cirrus clouds only produce fall streaks.
  Jet stream-powered cirrus can grow long enough to stretch across continents while remaining only a few kilometers deep. When visible light interacts with the ice crystals in cirrus cloud, it produces optical phenomena such as sun dogs and halos.
context_section_description: Thunderstorms can form dense cirrus at their tops. As the cumulonimbus cloud in a thunderstorm grows vertically, the liquid water droplets freeze when the air temperature reaches the freezing point. The anvil cloud takes its shape because the temperature inversion at the tropopause prevents the warm, moist air forming the thunderstorm from rising any higher, thus creating the flat top. In the tropics, these thunderstorms occasionally produce copious amounts of cirrus from their anvils. High-altitude winds commonly push this dense mat out into an anvil shape that stretches downwind as much as several kilometers.
  Individual cirrus cloud formations can be the remnants of anvil clouds formed by thunderstorms. In the dissipating stage of a cumulonimbus cloud, when the normal column rising up to the anvil has evaporated or dissipated, the mat of cirrus in the anvil is all that is left.
caption: Cirrus in an anvil cloud
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