Cumulus are fair-weather, water-droplet clouds that are detached from one another.
Cumulus clouds have well-defined, flat bases and domed tops that resemble a cauliflower. Because they are fair-weather clouds, their outlines are usually sharply defined against a blue sky. They sometime resemble rising mounds, domes, or towers.
The sunlit parts of a cumulus cloud will be brilliant white; the base will be relatively dark.
Cumulus clouds in one area of the sky commonly form at the same altitude which is the condensation level of the rising air currents.
There are small cumulus clouds and swelling cumulus clouds. Small cumulus clouds are common during the warm season. Rain does not fall from small cumulus clouds.
Swelling cumulus clouds–also called towering cumulus and cumulus congestus–are towering clouds that can dominate the sky. Swelling cumulus clouds are taller than they are wide; they can be a collection of separate, smaller clouds that become somewhat organized by the wind.
Towering cumulus clouds that form early in the day can be a sign of a storm to come later in the day.