What are upwardly billowing clouds?

Clouds that develop vertically are called cumulus clouds. If these clouds produce a thunderstorm, they are called cumulonimbus. Cumulonimbus clouds are much larger and more vertically developed cumulus clouds, with the tops reaching 39,000 feet or higher.

Water, ice crystals and other small particles in the atmosphere form clouds. Clouds are named for how they are formed and how high they are in the atmosphere. Cumuliform clouds are puffy, while stratoform clouds are flat. Some clouds form high in the atmosphere at altitudes between 16,000 and 45,000 feet. These clouds include cirrus, cirrostratus and cirrocumulus clouds. Clouds occurring between 6,500 and 22,000 feet include altostratus, altocumulus and nimbostratus varieties.