a cloud of a class indicative of thunderstorm conditions characterized by large, dense towers that often reach altitudes of 30,000 ft (9000 m) or more, cumuliform except for their tops, which appear fibrous because of the presence of ice crystals
An extremely dense, vertically developed cumulus with a relatively hazy outline and a glaciated top extending to great heights, usually producing heavy rains, thunderstorms, or hailstorms
A vertically developed cloud, often capped by an anvil shaped cloud Also called a thunderstorm cloud, it is frequently accompanied by heavy showers, lightning, thunder, and sometimes hail or gusty winds
A principal cloud type, exceptionally dense and vertically developed, occurring either as isolated clouds or as a line or wall of clouds with separated upper portions These clouds appear as mountains or huge towers, at least a part of the upper portions of which are usually smooth, fibrous, or striated, and almost flattened This part often spreads out in an anvil shape (incus) or vast plume Under the base of a cumulonimbus, which often is very dark, there frequently exists virga, precipitation, and low, ragged clouds, either merged with it or not Its precipitation is often heavy and always of a showery nature The usual occurrence of lightning and thunder within or from this cloud leads to its common names, thundercloud, thunderhead (usually refers only to the upper portion of the cloud), and thunderstorm
A cumulus cloud of significant vertical extent This cloud often has an anvil shaped appearance on top This cloud is also known as a thunderhead, and tends to produce heavy showers, accompanied at times by lightning, gusty winds and hail
A vertically developed cumulus cloud, often capped by an anvil shaped cloud Also called a thunderstorm cloud, it is frequently accompanied by heavy showers, lightning, thunder, and sometimes hail or gusty winds
A vertically developed cumulus cloud, often capped by an anvil-shaped cirriform cloud Also called a thunderstorm cloud, it is frequently accompanied by heavy showers, lightning, thunder, and sometimes hail, tornadoes or strong, gusty winds
These large, heavy and dense clouds have a flat dark surface and large tops shaped like mountains They are generally associated with lightning, thunder, halo and sometimes tornadoes