Cloud types / Cumulonimbus

Cumulonimbus · Cb

Cumulonimbus is an enormous, dense cloud with substantial vertical extent, rising like huge mountains or towers into the upper troposphere. Its upper portion is smooth, fibrous, or striated, often flattened into an anvil shape. This genus is critical in weather monitoring because it represents extreme atmospheric convection and is the sole cloud genus capable of producing severe thunderstorms, torrential downpours, lightning, hail, and damaging wind gusts.

How it forms

Cumulonimbus forms through vigorous atmospheric convection within an unstable air mass possessing abundant moisture and strong lift. Towering cumulus clouds ascend rapidly until their tops reach freezing altitudes, transforming water droplets into ice crystals and giving the cloud summit a smooth, fibrous, or flattened appearance.

Identification keys

• Massive vertical stature extending from low altitudes to the tropopause
• Fibrous, glaciated summits often spreading out into a classic anvil (incus)
• Very dark, turbulent bases frequently accompanied by low ragged clouds
• Distinct precipitation curtains or shafts visible trailing beneath the base
• Smooth or striated upper edges formed purely of ice crystals

Typical weather

Cumulonimbus brings severe, turbulent weather including heavy showers, thunderstorms, hail, and strong gusty winds. It is the only cloud that produces thunder and hail, with intense precipitation occurring in localized bursts rather than steady, uniform rain.

Often confused with

Photography tip

Step back to capture the full storm profile from several miles away, capturing both the dark base and the illuminated anvil.

Questions about this cloud

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