Description & Characteristics. The ‘calvus’ cloud species is one of only two species that’s associated with cumulonimbus clouds. No other cloud type besides a cumulonimbus cloud can receive a calvus classification. Translated from latin, meaning bald, a cloud that’s classified as cumulonimbus calvus can be best identified through the puffy and cumuliform appearance at the top of the cloud. The proper cloud classification abbreviation for this cloud is ‘Cb cal’.
The precursor to these clouds are usually cumulus congestus clouds, and can be differentiated through a darker base, thunder, lightning, precipitation, all of which are features of cumulonimbus clouds. Depending on the conditions, these clouds can morph from a cumulus congestus, to a cumulonimbus calvus, to a cumulonimbus capillatus incus (thunderstorm with an anvil cloud) within the matter of minutes.
Other cloud features and accessories that might be associated with these clouds include pileus (cap cloud), virga (evaporating rain strips), and praecipitatio (rainfall). On the rare occasion, a fire could assist with the formation of these clouds, which would give the cloud a classification of cumulonimbus calvus flammagenitus.
Clouds identified as cumulonimbus calvus aren’t particularly common, and often might be difficult to classify if the cloud is right above you or if other clouds are obstructing your view.