Cumulonimbus

This is a photograph of a cumulonimbus cloud. Notice how the top of the cloud is shaped like an anvil. Click on image for full size version (22K JPG) Courtesy of University Corporation for Atmospheric Research

Cumulonimbus (weather symbol - Cb) clouds belong to the Clouds with Vertical Growth group. They are generally known as thunderstorm clouds. A cumulonimbus cloud can grow to such heights that it actually reaches the tropopause. At this height, high winds will flatten the top of the cloud out into an anvil-like shape. Cumulonimbus clouds are associated with heavy rain, snow, hail, lightning, and tornadoes.