Opacus

Definition

A cloud variety describing a layer thick and opaque enough that the sun or moon cannot be seen through it at all. It applies to altocumulus, altostratus, stratocumulus and stratus.

Field note

Opacus is the closed form and it is the one that persists. A closed stratocumulus deck that is still closed at 09:00 local time will often stay closed all day; an open perlucidus deck at the same hour usually opens further.

Related terms

• Perlucidus · perlucidus
• Stratocumulus · Stratocumulus
• Translucidus · translucidus