Opacus Cloud Variety:Opaque, Hides the Sun or Moon

Learn how to identify opacus clouds, whose opaque layer hides the Sun or Moon, with photographs, illustrations, and valid parent cloud types.

Stratus opacus undulatus (St op un)
Stratus opacus undulatus (St op un)

Identifying the opacuscloud variety

A cloud variety describing a cloud of thick and darkened characteristics

The ‘opacus’ cloud variety can be found amongst four cloud types: altocumulus, altostratus, stratus, and stratocumulus. Translated from latin, meaning darkened, the four types of opacus clouds are respectively abbreviated as ‘Ac op’, ‘As op’, ‘St op’, and ‘Sc op’. Of the nine cloud varieties, this is arguably the easiest to identify.

Plain and simple, opacus cloud formations are dark clouds where you cannot see the sun. It’s important to note that the opacus cloud variety is the opposite of the translucidus cloud variety. If you can see the sun shining through the cloud or make out the sun’s position in one of these four cloud types, classify the cloud as translucidus.

If not, the mark it as opacus. Even though clouds can have more than one variety applied to it, a cloud cannot be classified as opacus and translucidus simultaneously.. As a cloudspotter, the opacus variety is one of the more popular varieties in altostratus and stratus clouds.

It’s also important to note that more often than not, you’ll find the opacus cloud variety in altocumulus and stratocumulus clouds when they’re of the stratiformis cloud species.

Opacus and its cloud types

Opacus can modify each cloud type shown below. Compare how the same term appears across different levels and broader cloud forms.

Compare opacus with related cloud varieties

Use the defining shape, arrangement, associated cloud type, and full sky context before selecting the most appropriate term.

Opacus vs. translucidus

Opacus is dense enough to hide the Sun or Moon. Translucidus remains thin enough for the position of the Sun or Moon to be visible through it.

Illustration of opacus clouds
Opacus
Illustration of translucidus clouds
Translucidus

See opacus cloud classifications in action

Follow real photographs through the visible clues that lead to each complete cloud classification.

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