Cumulonimbus clouds are large, vertically developed clouds that have strong updrafts and are made up of water droplets in the lower levels with ice crystals in their upper portions. When the cloud grows to a point that it reaches a stable layer, typically the tropopause (the level separating the troposphere where most of our weather occurs and the stratosphere above), it spreads out horizontally creating what’s called an anvil. This cloud is then referred to as cumulonimbus incus.
Location: Fort Collins, CO
Date: May 2006