Cumulonimbus clouds are storm clouds. Clouds are large collections of water droplets that can be frozen, but only sometimes. They form due to condensation, when water evaporates into a gas and cools down above the Earth. Then, the water drops attach to pieces of dust or dirt that are above the Earth. As more droplets attach to one piece of debris, they form a water drop. Then, when the cloud gets heavy and full of water, it rains or snows! These clouds have so much water, but what keeps it all from falling until the cloud is a cumulonimbus or storm cloud? It is because of updrafts or powerful gusts of wind blowing from the ground to the sky!