Clouds that look like cotton balls are called cumulus clouds. They form when warm, moist air rises. As this air rises, it cools, condensing into water droplets that become puffy clouds. Cumulus clouds develop from the bottom upward.
The bottoms of cumulus clouds are flat and typically lie about 3,000 feet above the ground. As the cumulus cloud grows in height, it can produce stormy weather. Cumulus congestus and towering cumulus clouds are cumulus clouds that have developed vertically but have not become thunderstorms yet. If the atmosphere becomes more unstable and more moisture accumulates, these tall cumulus clouds become cumulonimbus clouds. Cumulonimbus clouds can produce heavy rain, snow, hail, lightning and tornadoes.