What are cumulus clouds?

Cumulus clouds are the common clouds that look like puffy balls of cotton, and may be well-defined within open sky. In unstable air, they can become very tall and may lead to the formation of thunderclouds (cumulonimbus).

A cumulus cloud is one of the three basic cloud forms (the others are cirrus and stratus). It is also one of the two low cloud types, a cloud that develops in a vertical direction from the base (bottom) up. It has a flat base and dome- or cauliflower-shaped upper surfaces. The base of the cloud is often no more than 3,000 feet above the ground, but the top often varies in height. Small, separate cumulus are associated with fair weather (cumulus humilis). With additional heating from the earth's surface, clouds can grow vertically throughout the day. The top of such a cloud can easily reach 20,000 feet or more into the troposphere. Under certain atmospheric conditions, these clouds can develop into larger clouds, known as towering cumulus (cumulus congestus), and may produce a rain shower. Further development may create a cumulonimbus, or thunderstorm cloud.

Cumulus clouds are formed by convection and are generally found between 3000-7000 feet in the summer, but as low as 700 feet in the winter. They consist of of water droplets which are cooled but above the freezing level.