Cumulonimbus

Cumulonimbus is a tall, dense, vertically developed cloud associated with strong convective activity and thunderstorm production. It forms when moist air rises in an unstable atmosphere, driven by surface heating, convergence, or lifting along weather fronts and drylines. The cloud grows from cumulus congestus into cumulonimbus as updrafts intensify, with the mature stage producing heavy precipitation, lightning, and strong winds.

Anatomy and structure include a broad, dark base and a towering vertical extent that can reach into the upper troposphere. The upper portion often fans out into an anvil shape called the incus when the updraft reaches the tropopause and the cloud top spreads horizontally. In highly developed storms, overshooting tops may protrude above the tropopause. Typical vertical development ranges from near the surface to about 12–16 kilometers (40,000–52,000 feet) in mid-latitudes, with greater heights possible in tropical regions.

Weather and impacts associated with cumulonimbus include intense rainfall, hail, lightning, thunder, and strong winds. Downdrafts can produce microbursts and gust fronts, and in some environments tornadoes may form in and around the mature cloud. Visual indicators include a dark, towering base and anvil top, sometimes accompanied by mammatus cloud formations on the underside.

Cumulonimbus occurrences are common in warm, humid climates and during times of strong atmospheric instability, including summer afternoons in continental interiors and along tropical rain belts. They are a primary source of severe weather and aviation hazards.