Description & Characteristics. The ‘capillatus’ 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 capillatus classification. Translated from latin, meaning having hair, a cloud that’s classified as cumulonimbus capillatus can be best identified through the fibrous and cirriform appearance at the top of the cloud. The proper cloud classification abbreviation for this cloud is ‘Cb cap’.
The precursor to these clouds is usually cumulonimbus calvus clouds. Cumulonimbus capillatus clouds can signify a more mature thunderstorm, with strong wind, hail, and lightning. Well-developed cumulonimbus capillatus clouds are often paired with anvil clouds (incus). Cumulonimbus capillatus inclus clouds are arguably the most powerful standalone clouds in our atmosphere and a favorite amongst storm chasers . Additionally, these clouds can be accompanied by other cloud features and accessories such as shelf clouds (arcus), mammatus clouds (mamma), wall clouds (murus), precipitation (praecipitatio), evaporating rain strips (virga), cloud veil cloud formations (velum), and even the elusive funnel cloud or tornado (tuba). Seeing a cap cloud (pileus) formation is generally an indication of a rising cumuliform updraft, so generally this cloud feature isn’t seen with the capillatus species.
Cumulonimbus capillatus clouds don’t always signify severe weather however. There are versions of cumulonimbus capillatus clouds where the top is hairy because it’s in the process of being dismantled by turbulent winds in the upper troposphere. A dying thunderstorm can result in the cloud dissipating. As this happens, it might leave behind the remains of the top section of the cloud (which can include the anvil) and morph into a cirrus spissatus.
Clouds identified as cumulonimbus capillatus aren’t particularly common, and might be difficult to classify if the cloud is right above you or if other clouds are obstructing your view.