Altocumulus cloud

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Altocumulus cloud formation
Abbreviation	Ac
Symbol
Genus	Alto- (high), -cumulus (heap)
Altitude	2400-6100 m (8,000-20,000 ft)
Classification	Family B (Medium-level)
Precipitation Cloud?	No

Altocumulus (alto, "high", cumulus, "heaped") is a cloud belonging to a class characterized by globular masses or rolls in layers or patches, the individual elements being larger and darker than those of cirrocumulus and smaller than those of stratocumulus. Like other cumulus clouds, altocumulus signifies convection. It is usually white or gray, and often occurs in sheets or patches with wavy, rounded masses or rolls. Altocumulus often are seen preceding a cold front, and their presence on a warm, humid, summer morning frequently signals the development of thunderstorms later in the day.

One form of altocumulus, altocumulus lenticularis (Lenticular cloud) is frequently reported as "UFOs".

Altocumulus in a clear mackerel pattern

Mackerel sky over Lincolnshire, UK.

Mackerel Sky

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Altocumulus clouds

v • d • e Clouds
High Clouds (Family A):	Cirrus (Ci) • Cirrus uncinus • Cirrus Kelvin-Helmholtz colombia • Cirrostratus (Cs) • Cirrocumulus (Cc) • Pileus • Contrail
Middle Clouds (Family B):	Altostratus (As) • Altostratus undulatus • Altocumulus (Ac) • Altocumulus undulatus • Altocumulus mackerel sky • Altocumulus castellanus cloud • Altocumulus lenticularis
Low Clouds (Family C):	Stratus (St) • Nimbostratus (Ns) • Cumulus humilis (Cu) • Cumulus mediocris (Cu) • Stratocumulus (Sc)
Vertical Clouds (Family D):	Cumulonimbus (Cb) • Cumulonimbus incus • Cumulonimbus calvus • Cumulonimbus with mammatus • Cumulus congestus • Pyrocumulus • Pyrocumulonimbus