Description & Characteristics. The ‘castellanus’ cloud species can be found amongst four cloud types: cirrus, cirrocumulus, altocumulus, and stratocumulus. Translated from latin, meaning castle, the four types of castellanus clouds are respectively abbreviated as ‘Ci cas’, ‘Cc cas’, ‘Ac cas’, and ‘Sc cas’. When looking for castellanus clouds, keep your eye out for rising cumuliform towers usually with a connected base.
The castellanus species of cloud is uncommon, but can be expected to be seen on days when the atmosphere is unstable. Altocumulus castellanus clouds are sometimes abbreviated as ACCAS and are a particular favorite kind of cloud amongst storm chasers because they usually point to unstable air, which can mean for thunderstorm development sometime during the day. Castellanus clouds in the morning indicate stormy weather in the afternoon.
As a cloudspotter, it’s easier to spot castellanus clouds in stratocumulus and altocumulus clouds compared to cirrocumulus and cirrus clouds simply because they’re easier to see with the naked eye and perhaps a bit more common. It takes a keen eye to notice the castellanus cloud species in cirrus and cirrocumulus clouds. Don’t confuse them with cumulus congestus clouds, which are differentiated as individual clouds and aren’t connected at the base like castellanus clouds are.
Castellanus cloud formations can be found paired with cloud varieties duplicatus (multilayered) and radiatus (parallel bands and strips), as well as with virga (evaporating rain strips) on occasion.
