Here’s a photograph taken in the evening in central Virginia in September 2019. It was a warm afternoon with calm, partly cloudy skies.
Summary: These clouds are mid-altitude puff balls almost resembling a flock of sheep, classified as altocumulus floccus (Ac flo).
Cloud Type. First, let’s figure out the cloud type. These cumuliform clouds clumped together. The word cumuliform describes a cloud that is of the heaped or a puffy cloud formation (similarly, the word stratiform means a layer-like cloud formation).
The five cumuliform cloud types are cumulus, stratocumulus, cumulonimbus, altocumulus, and cirrocumulus clouds. These clouds aren’t producing thunderstorms and don’t seem particularly high in altitude, eliminating cumulonimbus and cirrocumulus.
Both altocumulus and stratocumulus clouds are generally seen as groups of clouds found in rolls, sheets or heaps where cumulus clouds are more often seen as individual clouds. That’s the case here… let’s eliminate cumulus clouds.
When deciding between stratocumulus and altocumulus clouds, remember that their altitude differentiates them the most, with altocumulus clouds being higher in altitude.
Sometimes it’s difficult to tell the difference between high-based stratocumulus clouds and low-based altocumulus clouds. The clouds pictured don’t seem particularly close to the ground. It’s a close call, but we’ll say that these are low-based altocumulus clouds.
Cloud Species. There’s a lot of variations in altocumulus clouds. As we determine the species, we know that altocumulus clouds are associated with five cloud species: castellanus, floccus, lenticularis, stratiformis, and volutus.
By process of elimination, we can determine that these aren’t lenticularis (lens or UFO-shaped), stratiformis (layer-like, covering the sky), or volutus (roll cloud).
We’re left with castellanus (towered) and floccus (puffy and ragged). These clouds are particularly puffy, resembling a flock of sheep. This is a good indication that these can be classified as the floccus cloud species.
Cloud Varieties. Altocumulus clouds can have no cloud varieties present or they can have multiple. When it comes to cloud varieties, altocumulus clouds have seven associated cloud varieties: duplicatus, lacunosus, opacus, perlucidus, radiatus, translucidus, and undulatus.
In this case, there isn’t any that fit the bill. They aren’t multilayered (duplicatus), they don’t have holes in them (lacunosus), they aren’t particularly dark or thin (opacus or translucidus), they aren’t lined up in rows (radiatus), and they aren’t undulating (undulatus).
You might think you could apply the perlucidus cloud variety (transparent by small gaps) here, but generally the perlucidus cloud variety refers to the small gaps in clouds usually found in the stratiformis cloud species. The clouds in our example are separated cloud heaps with large amounts of blue sky in between.
Supplementary Features. Altocumulus clouds have five supplementary features: asperitas (chaotic and wavy underside), cavum (fallstreak hole, hole punch cloud), fluctus (wave features known as Kelvin-Helmholtz instability), mamma (mammatus clouds shaped like cow udders), and virga (evaporating precipitation). Inspecting the clouds in the photograph, none of these apply.
Cloud Accessories & Other Clouds. We’re done! Altocumulus clouds don’t have any associated accessory clouds or other clouds for that matter.
We determined the cloud classification starting from the cloud type and working our way down through its species, varieties, features, and accessories taxonomy. Our final classification is in: Altocumulus floccus (Ac flo).
