Description & Characteristics. The ‘velum’ cloud accessory can be found amongst two cloud types: cumulonimbus and cumulus. Translated from latin, meaning veil, the two types of velum clouds are respectively abbreviated as ‘Cb vel’, and ‘Cu vel’. Velum clouds are also called cloud veils and can be identified as horizontal altostratus cloud layers surrounding a cumulonimbus or cumulus congestus cloud, similar to a hula hoop.
Velum cloud accessories are closely related to cap clouds (pileus cloud accessory). They form on a much wider scale and last longer however, and can stick around even after the parent cloud has started to dissipate. Velum cloud formations are formed as the parent cloud meets a stable layer of air during its growth stage. The result is condensed air that’s spread out into an altostratus-like formation that surrounds the entire cloud formation.
As a cloudspotter, velum clouds are uncommon and easy to miss considering how boring of a cloud they tend to be, so it does take a keen eye to spot one. Similar to how you might mistake scud clouds (pannus cloud accessory) for stratus fractus clouds, it’s possible to observe a velum cloud formation but mistake it for a simple, unassuming layer of altostratus.