Anvil Cloud

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anvil cloud

[′an·vəl ‚klau̇d]
The popular name given to a cumulonimbus capillatus cloud, a thunderhead whose upper portion spreads in the form of an anvil with a fibrous or smooth aspect; it also refers to such an upper portion alone when it persists beyond the parent cloud.

Anvil Cloud


a cumulonimbus cloud whose top part is flattened out in the shape of an anvil of solid or fibrous structure and has a bright white color in sunlight. The anvil cloud consists of ice crystals and forms when a cumulonimbus cloud reaches a level with a temperature on the order of —10°C and lower.


The flat, spreading top of a Cb (cumulonimbus), often shaped like an anvil. Thunderstorm anvils may spread hundreds of miles (or kilometers) downwind from the thunderstorm. Sometimes, they may spread upwind, and are called back-sheared anvils. Also called an anvil cloud.
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Generally, storms of this magnitude have well-developed anvil tops; one of the "classic weather text" warnings about thunderstorms is to avoid "severe" thunderstorm clouds by at least 20 miles and avoid flying beneath anvil clouds at any distance from the cloud boundary.