[Latin: ‘heap’ + ‘raincloud’]
One of the cloud genera. A large, towering cloud of great vertical extent, with a dark, ragged base from which rain, hail, or snow is falling, often in the form of virga (Plate 8). The cloud usually shows signs of vigorous convection, and the tops (which appear brilliantly white when illuminated by the Sun) are glaciated and may appear smooth (Plate 8), fibrous, or striated, or be flattened into an anvil (incus: Plate 9). Individual cumulonimbus cells pass through three stages: growing (lasting c.20 minutes), mature (c.20 minutes), and decaying (30–120 minutes). Associated cloud species and accessory clouds are calvus and capillatus; pannus, pileus, and velum. Cumulonimbus are shower clouds, and may occur as thunderstorms, multicell storms, and supercell thunderstorms. Supplementary cloud features sometimes visible include arcus, mamma, and tuba. See also shower.