Altocumulus Clouds: Mid-altitude Cloud Heaps

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Definition: Middle-altitude cumuliform clouds often arranged in heaps or rolls

Description & Characteristics. Altocumulus clouds are typically found in groups or heaps clumped together. They’re found in the middle layer of the troposphere, lower than cirrocumulus and higher than their cumulus and stratocumulus counterparts. The term mackerel sky is also common to altocumulus (and cirrocumulus) clouds that display a pattern resembling fish scales. Of all the ten different cloud types, you’ll probably find that altocumulus clouds are the one of the most diverse and dynamic in terms of appearance.

These clouds can take on a handful of shapes and sizes. They can include cloud heaps that resemble towering castles (castellanus cloud species), can sometimes resemble a lock of wool (cloud species floccus), can cover the entire sky on occasion (stratiformis cloud species), and can even create horizontal tube-like structured clouds (volutus cloud species).

Altocumulus are also known for creating UFO-shaped clouds (lenticularis cloud species), are responsible for a lot of the fallstreak hole sightings (i.e. hole punch clouds) you might be lucky enough to see (cavum cloud feature), and on the rarest of occasion, can produce a wavy, chaotic appearance (asperitas cloud feature).

Altocumulus (Ac)
Altocumulus stratiformis perlucidus translucidus (Ac str pe tr)
Altocumulus stratiformis (Ac str)
Altocumulus lenticularis (Ac len)
Altocumulus floccus (Ac flo)
Altocumulus stratiformis perlucidus undulatus (Ac str pe un)
Altocumulus stratiformis mamma (Ac str mam)
Altocumulus perlucidus (Ac pe)
Altocumulus (Ac)

Altocumulus Cloud Facts

  • Cloud Level (Étage): ….. Middle
  • Altitude/Height: ……… 2-7km (7,000-23,000 ft)
  • Latin Term: …………… Derives from alto-, meaning high, and cumulo-, meaning heap
  • Abbreviation: ………… Altocumulus can be abbreviated as Ac
A bar graph showing the visual color of an altocumulus cloud

Cloud Color

White to gray

A bar graph showing the precipitation potential of an altocumulus cloud

Precipitation Potential

Virga only

A bar graph showing the amount of sky cover from an altocumulus cloud

Sky Cover

Mostly cloudy to mostly sunny

A bar graph showing how common observing an altocumulus cloud might be

Cloud Frequency

Very common

Altocumulus Cloud Species

Altocumulus clouds have five associated cloud species: castellanus, floccus, lenticularis, stratiformis, and volutus.

A graphical illustration of an altocumulus castellanus cloud

Altocumulus castellanus

Rising towers, turrets

A graphical illustration of an altocumulus floccus cloud

Altocumulus floccus

Puffy, ragged tufts

A graphical illustration of an altocumulus lenticularis cloud

Altocumulus lenticularis

Lens-shaped, resembling a UFO

A graphical illustration of an altocumulus stratiformis cloud

Altocumulus stratiformis

Horizontal, layer-like form

A graphical illustration of an altocumulus volutus cloud

Altocumulus volutus

Tube-shaped roll cloud

Altocumulus Cloud Varieties

Altocumulus clouds have seven associated cloud varieties: duplicatus, lacunosus, opacus, perlucidus, radiatus, translucidus, and undulatus.

A graphical illustration of an altocumulus lacunosus cloud

Altocumulus lacunosus

Perforated, round frayed holes

A graphical illustration of an altocumulus opacus cloud

Altocumulus opacus

Opaque, masks the sun

A graphical illustration of an altocumulus perlucidus cloud

Altocumulus perlucidus

Transparent by small gaps

A graphical illustration of an altocumulus radiatus cloud

Altocumulus radiatus

Parallel bands and strips

A graphical illustration of a altocumulus translucidus cloud

Altocumulus translucidus

See-through, sun’s position visible

A graphical illustration of an altocumulus undulatus cloud

Altocumulus undulatus

Wavelike, undulating

Altocumulus Cloud Supplementary Features

Altocumulus clouds have five supplementary features: asperitas, cavum, fluctus, mamma, and virga.

A graphical illustration of an altocumulus asperitas cloud

Altocumulus asperitas

Chaotic, wavy underneath

A graphical illustration of an altocumulus cavum cloud

Altocumulus cavum

Fallstreak hole, hole punch

A graphical illustration of an altocumulus fluctus cloud

Altocumulus fluctus

Kelvin-Helmholtz waves, curls

A graphical illustration of an altocumulus mamma cloud

Altocumulus mamma

Sac-like, resembling cow udders

A graphical illustration of an altocumulus virga cloud

Altocumulus virga

Evaporating rain strips

Altocumulus Cloud Accessories & Other Clouds

Altocumulus clouds don’t have any associated accessory clouds or other clouds associated with this cloud type. ⛅

Similar Cloud Types

Altocumulus vs. Altostratus

While altocumulus and altostratus clouds are found at the same altitude, altostratus clouds are generally a featureless layer, where altocumulus clouds typically have plenty of features. Altostratus clouds don’t have any cloud species associated with them, so if you’re deciding between an altostratus and altocumulus cloud and the cloud you’re observing looks to have an associated cloud species, you should learn towards an altocumulus cloud.

Altocumulus vs. Cirrocumulus

Altocumulus and cirrocumulus clouds share many of the same cloud species, but cirrocumulus clouds are higher in altitude, so their cloudlets appear smaller. Cirrocumulus clouds are more often than not seen with cirrus and cirrostratus clouds in near proximity. Altocumulus clouds are also more commonly observed than cirrocumulus. It’s more common to see the entire sky covered by a layer of altocumulus clouds than cirrocumulus clouds.

Altocumulus vs. Cumulus

Altocumulus clouds are generally seen as patches of clouds grouped together, either in rolls, sheets or heaps. Cumulus clouds are more often seen as individual clouds. Cumulus clouds are also much closer to the ground. A key reminder trying to determine the difference between cumulus and altocumulus clouds are that the two cloud types don’t have any shared cloud species.

Altocumulus vs. Stratocumulus

Altocumulus clouds are more closely related to stratocumulus clouds than they are to cumulus clouds. They share almost all of the same cloud species, cloud varieties, and other cloud features. Their altitude however differentiates them the most, with stratocumulus clouds being closer to the ground. Hence, stratocumulus cloud formations are seemingly bigger, and are generally a bit darker than altocumulus clouds.