These clouds usually have flat bases and lumpy tops.
Cumulus clouds are usually very isolated with large areas of blue sky in between the clouds.
Most cumulus clouds form below 6,000 feet and are relatively thin and associated with fair weather. However, when the atmosphere becomes unstable and very strong, upward air currents form, cumulus clouds can grow into cumulus congestus, or towering cumulus. If the atmosphere is unstable enough, cumulonimbus clouds, better known as thunderstorms, form. Cumulus congestus and cumulonimbus clouds can tower from below 6,000 feet to greater than 50,000 feet.