From Cumulus to Cirrus: Exploring the Diversity of the Sky

4. Cumulonimbus: The Thundercloud Giants

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Often known as thunderheads, cumulonimbus clouds are the cloud world's skyscrapers. Penetrating somewhat deeply into the troposphere and occasionally into the stratosphere, these enormous, towering clouds can reach heights of 75,000 feet or more from as low as 1,000 feet. One of the most amazing and maybe dangerous cloud forms because of their great vertical development, which is evidence of the strong atmospheric forces acting in their production. Thunderstorms, torrential precipitation, and occasionally severe storms including tornadoes and hail come mostly from these clouds. Usually with a dark, flat base and a top shaped like anvil or mushroom generated by high winds in the upper sky, a mature cumulonimbus cloud looks like Often among the earliest indicators of a storm's arrival is this unique anvil form. A cumulonimbus cloud's life cycle is a striking exhibition of natural force. Starting as a little cumulus cloud, it expands quickly as warm, moist air rises within it. Rising air cools and condenses, producing latent heat that drives more expansion. The cloud moves toward a point at where it can generate lightning, thunder, and heavy rain. For meteorologists and weather forecasters, cumulonimbus clouds are a vital focus since their existence usually indicates unstable atmospheric conditions and the possibility for strong storms. A sophisticated interaction of updrafts and downdrafts occurs inside a cumulonimbus cloud. Water droplets carried high into the cloud by strong updrafts freeze to create hail. Rising in size until they are too heavy and fall to the ground, these hailstones can move within the cloud. As this is happening, the strong electrical charges accumulating inside the cloud produce the amazing lighting shows connected with thunderstorms.