Cumulus clouds are fluffy, white clouds that often resemble cotton balls. They typically form in fair weather and indicate that the atmosphere is stable. These clouds develop when warm, moist air rises and cools, causing water vapor to condense into tiny droplets. Cumulus clouds can grow larger and develop into more complex cloud types, such as cumulonimbus, which can produce thunderstorms. Cumulus clouds are usually seen during the daytime when the sun heats the Earth's surface. They can vary in size and shape, often appearing puffy and well-defined. While they generally signal pleasant weather, larger cumulus clouds can indicate changing conditions, leading to precipitation or storms.