Plain English Meaning

Areas of sky filled with the cotton-ball type clouds that form when warm air rises and its moisture condenses. When you see them spread across the sky, it means the air below is bumpy and rising in many places at once.

Full Definition

Layers or fields of puffy, heaped clouds with flat bases and rounded tops, formed by rising columns of warm air (convective currents) reaching their condensation level. The presence of cumulus cloud layers indicates active convection in the atmosphere below them.

Context Anchor

Seen in weather study, preflight weather planning, and in flight when looking outside to judge where rising air and bumps may be present.

Derivation

Cumulus comes from the Latin word for 'heap' or 'pile.' The name the : heaped, mounded clouds stacked up by rising air.