Altocumulus stratiformis

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.

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

Formation

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.