Height of base:

below 600 m (2000 ft)

Height of top:

5-12 km  (45000 ft) (tropopause)

Description:

Thunderstorm cloud,

Massive, heavy;

 dark base;

Fibrous top if freezing ;

Thunder and lightning

Occurrence:

Tropical and moderate regions, rare in polar regions

Made of:

water droplets, supercooled water droplets, ice crystals in tops

Precipitation:

Heavy downpours; possibly hail

Formation:

Unstable air, selfsustaining convection, top at inversion of tropopause

Species:

Calvus, capillatus

How to distinguish from …

… Nimbostratus (Nb)

Nb has lighter, steadier precipitation, no thunder or lightning, covers much of sky.

Cb heavy showers, thunder and lightning, cloud boundaries may be noticeable

Cumulus congestus (Cu con)

Freezing in upper layer of Cb leads to soft edges, fibrous structure

Presence of thunder in Cb

Cumulonimbus calvus with velum

(Hebgen Lake, Mt, June2006)

Cumulonimbus capillatus

(Morris, June 2006)

Cumulonimbus at the end of its life cycle

(Morris, June 2006)

Cumulonimbus capillatus with

mammatus and velum

(Morris, June 2007)

Cumulonimbus with roll cloud

Morris, June06

Cumulonimbus cappilatus

Yellowstone NP, July06

Roll cloud (arcus) in front of cumulonimbus capillatus incus

Yellowstone, July06

Rain core of cumulonimbus

Yellowstone Lake, July 06

Inflow band

Yellowstone NP, July06

Cb, South Dakota, July06

Cumulonimbus calvus with rain core

Badlands, SD, July06

Backside of cumulonimbus

Morris, June06

Cb with wall cloud. A brief tornado touchdown

Was observed 3 miles NE of Morris. May 2008

Same as left, 10 min later

AVI timelapse clip of SW corner

Of the May-31-2008 storm.

Note the horizontal

rolling motion. Edge of anvil visible toward the end of clip. View toward NW.

Storm was moving from NW.

Filmed during tornado warning.