Height of base:

below 600 m (2000 ft) (low-level clouds)

Description:

Heap-like

cauliflower tops; fluffy rounded tops

flat bases

brilliant white; base can appear shadowed;

Occurrence:

World-wide, except Antarctica (no thermals)

Made of:

water droplets, supercooled water droplets

Precipitation:

None; cumulus congestus may precipitate brief showers

Formation:

convection in instable layer (thermals), capped by stable layer

Species:

Humilis, mediocris, congestus, fractus

Varieties:

Radiatus

How to distinguish from …

… Stratocumulus (Sc)

Clouds are detached, not joined into layer

Altocumulus (Ac)

Wider than three fingers at stretched arm, 30º above horizon

Cumulonimbus (Cb)

Develops from congestus

Congestus has a sharp cauliflower outline, no softness from ice crystals

Cumulus humilis

(Hebgen Lake, Mt, June2006)

Cumulus mediocris

(Yellowstone Nat Park,

June 2006)

Cumulus congestus embedded in stratocumulus,

Altocumulus (Morris, June07)

Cumulus mediocris

Morris, May 07

Cumulus congestus

Glenwood, May 07

Cumulus humilis

Morris, May06

Cumulus fractus

Morris, May06

Cumulus humilis

Fountain geyser, Yellowstone NP, June06

Cumulus fractus

(Morris, May 2007)