Height of base:

Between 2000 and 6000 m (6500 - 18000 ft) (mid-level clouds)

Description:

Patches of cloudlets, sheep clouds

Clumps, rolls or lenses with noticable shading and clear sky inbetween,

1º - 5º across (1 to 3 fingers at outstretched arm 30º above horizon)

Occurrence:

World-wide

Made of:

Supercooled water droplets, some ice crystals

Precipitation:

None; may have virga

Formation:

Too high fro thermals

Warm front (warm air sliding over colder air)

Species:

Stratiformis, lenticularis, castellanus, floccus

Varieties:

Opacus, translucidus, perlucidus, undulatus, duplicatus, radiatus, lacunosus

How to distinguish from …

Cirrocumulus (Cc)

Cc elements are smaller than one finger

Cc has no noticeable shading

Stratocumulus (Sc)

Cloud elements are larger than 3 fingers width at 30º above horizon

Cirrus (Ci)

Ac can have fall streaks resembling Ci, however Ci lacks the dense fluffy head

Altocumulus Stratiformis undulatus

(Morris, April 2006)

Altocumulus radiatus

(Morris, October 2006)

Altocumulus

(Morris, November 2006)

Altocumulus lenticularis

(Morris, September 2007)

Same as left, 5 minutes later

Altocumulus stratiformis opacus

Altocumulus radiatus

Morris, March 07

Altocumulus castellanus and cirrostratus

(Morris, May 07)

Altocumulus

Morris, August 06

Altocumulus floccus

Morris, Jan 2008

Altocumulus lenticularis

Morris, May16, 2008

Altocumulus with fall streaks (ice crystals)

Morris, April 20, 2008