Cloud types Flashcards
How are Cirrus clouds formed, what are they composed of and what weather do they result in?
Detached clouds in the form of white, delicate filaments, or white patches or narrow bands. Clouds have a fibrous (hair-like) appearance, or a silky sheen or both. Forms by wide spread ascent often associated with frontal lifting or convergence in a low pressure system - especially tropical cyclones. Also forms at the top of large cumulonimbus. Composed of ice crystals.
How are Cirrocumulus clouds formed, what are they composed of and what weather do they result in?
Thin sheet/layer of cloud containing many very small elements in the form of grains/ripples more or less regularly arranged. Forms by wide spread ascent associated with frontal lifting or convergence. Often associated with turbulence between two horizontal airflows in the upper atmosphere. Composed of ice crystals or a mixture with liquid droplets. Too high for significant icing.
How are Cirrostratus clouds formed, what are they composed of and what weather do they result in?
Thin sheet of transparent cloud often covering the entire sky and giving it a ‘milky’ appearance. Produces halo phenomena when thick enough. Forms by widespread ascent often associated with frontal lifting or convergence, or sometimes from the lifting of thin altostratus or smoothing of the elements in the cirrocumulus. Composed of ice crystals, too high for significant icing.
How are Altocumulus clouds formed, what are they composed of and what weather do they result in?
White or grey layer or merging layers of cloud. regularly arranged clumps/rolls visible. Formed by turbulence in the middle levels, usually below an inversion. Can also be caused by convection or orographic lifting in conditions of fairly low relative humidity. Composed of water droplets including supercooled water droplets. Occasionally results in some slight rain or snow from the cloud base, often evaporating before reaching the ground (virga). May be light rime ice.
How are Altostratus clouds formed, what are they composed of and what weather do they result in?
Grey or bluish layer of cloud. Often totally covering the sky. Parts are thin enough to reveal the sun vaguely. Forms by widespread ascent due to frontal lifting or convergence. Composed of water droplets, supercooled water droplets and ice crystals. When thick it can produce intermittent or continuous rain or snow. Virga is also common. Definite risk of moderate rime ice, clear ice possible in the lower levels of the cloud.
How are Nimbostratus clouds formed, what are they composed of and what weather do they result in?
Grey, often dark cloud layer. The base is often rendered indistinct due to continuously falling rain or snow. Low ragged clouds often occur beneath the base. Forms by wide spread ascent due to convergence, especially in the monsoonal trough, or slow moving fronts when the atmosphere is stable. Composed of water droplets with a mixture of ice crystals and liquid droplets near the top. Moderate to heavy continuous rain or snow. Definite risk of moderate rime ice, clear ice probable in the lower levels of the cloud.
How are Stratocumulus clouds formed, what are they composed of and what weather do they result in?
Grey or whitish layer containing darker elements as a chequered pattern or rolls. Forms by turbulence within the surface layers, or cumulus spreading out beneath an inversion. Composed of water droplets. Usually little, but light rain or drizzle is common. Occasional rime ice if flight is above freezing level.
How are Stratus clouds formed, what are they composed of and what weather do they result in?
Generally a grey cloud layer with a uniform base. Sometimes in the form of ragged patches. Forms by orographic or frontal lifting of stable air. Lifting of fog layers after sunrise. Composed of water droplets. Drizzle is typical in any.
How are Cumulus clouds formed, what are they composed of and what weather do they result in?
Detached clouds with sharp outlines. Usually in the form of rising mounds, base looks darker and is nearly flat. Forms by convection/lifting in conditionally stable layers of the atmosphere. Composed of water droplets, supercooled water droplets and ice crystals near the tops of large cells. Showers of rain or snow in larger cumulus and virga if base is high.
How are cumulonimbus clouds formed, what are they composed of and what weather do they result in?
Heavy, dense cumuliform cloud of great vertical extent. Part of its upper portions spreads out into a smooth anvil of cirrus cloud. Very dark beneath the base with ragged patches, rolling/swirling motions can be seen in the lower layers. Develops from normal cumulus due to any lifting mechanism when a considerable depth of the atmosphere is conditionally stable. Heavy showers of rain, hail or snow, lightning, squalls at the surface and occasionally torna does and water spouts. Sever to extreme turbulence. Definite risk of dangerous clear ice.
