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Altocumulus stratiformis

Species of Altocumulus cloud

Altocumulus stratiformis
Altocumulus stratiformis over Germany in 2011
Abbreviation	Ac str
Genus	Altocumulus (high, heaped)
Species	stratiformis
Variety	perlucidus undulatus
Altitude	2,000 - 6,000 m (6,500 - 20,000 ft)
Classification	Family B (Medium-level)
Appearance	Patchy and shallow; often semi-transparent.
Precipitation	Uncommon

Altocumulus stratiformis is the most common species of the Altocumulus genus of clouds.^[1] They tend to form broad layers of individual, cell-like clumps, often separated from each other, though they sometimes can coagulate into a larger individual cloud. They often have a vertical extent of less than 500 m.^[2] Due to their formation dynamics, they are commonly associated with the imminent arrival of precipitation.

The presence of stratiformis clouds in the mid-levels of the atmosphere is indicative of some instability at that level;^[3] atmospheric pressure falls, often associated with nearby systems of low pressure, can depress the altitude of stratiformis into the lower atmosphere, often evolving into Nimbostratus clouds, which precipitate. ^[4] Altocumulus stratiformis clouds may also form when a cold front is approaching, due to the difference in air masses.

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