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Opacus is a cloud variety that is found in stratocumulus, altocumulus, altostratus, and stratus cloud types. This cloud variety has a dark and opaque appearance and hides the location of the Sun and Moon. This makes it the opposite of translucidus, which is translucent and gives away the location of the Sun and Moon.^[1]

Opacus
Stratocumulus stratiformis opacus undulatus
Abbreviation	op
Genus	Altostratus, altocumulus, stratocumulus, stratus
Variety	opacus
Appearance	Opaque cloud cover that hides the location of the Sun or Moon
Precipitation	Depends on the cloud type this variety is appearing in

• Translucidus (cloud variety)
• Perlucidus (cloud variety)