Opacus (cloud variety)

Opaque cloud variety

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

References

^ "Learn About Opacus Clouds: Opaque, Masks the Sun".

Cloud genera and selected species, supplementary features, and other airborne hydrometeors - WMO Latin terminology except where indicated

Mesospheric

Extreme-level
80–85 km

Noctilucent (NLC) Polar mesospheric clouds	Noctilucent type I veils Noctilucent type II bands Noctilucent type III billows Noctilucent type IV whirls

Stratospheric

Very high-level
15–30 km

Nacreous polar stratospheric clouds (PSC)	Cirriform nacreous Lenticular nacreous
Nitric acid and water polar stratospheric clouds (PSC)	No differentiated sub-types; tends to resemble cirrostratus

Tropospheric

High-level
3–18 km

Cirrus (Ci)

Species	Cirrus castellanus (Ci cas) Cirrus fibratus (Ci fib) Cirrus floccus (Ci flo) Cirrus spissatus (Ci spa) Cirrus uncinus (Ci unc)
Ci-only varieties	Cirrus intortus (Ci in) Cirrus vertebratus (Ci ve)

Cirrocumulus (Cc)

Species	Cirrocumulus castellanus (Cc cas) Cirrocumulus floccus (Cc flo) Cirrocumulus lenticularis (Cc len) Cirrocumulus stratiformis (Cc str)

Cirrostratus (Cs)

Species	Cirrostratus fibratus (Cs fib) Cirrostratus nebulosus (Cs neb)

High-level-only
mutatus cloud

Mutatus non-height specific (see below)

Medium-level
2–8 km

Altocumulus (Ac)

Species	Altocumulus castellanus (Ac cas) Altocumulus floccus (Ac flo) Altocumulus lenticularis (Ac len) Altocumulus stratiformis (Ac str) Altocumulus volutus (Ac vol)

Altostratus (As)

Altostratus undulatus

Nimbostratus (Ns)
Multi-level

Varieties	Nimbostratus virga (Ns vir)

Low-level
0–2 km

Cumulonimbus (Cb)
Towering vertical

Species	Cumulonimbus calvus (Cb cal) Cumulonimbus capillatus (Cb cap)
Cb-only supplementary features	Cumulonimbus cauda ((cau) Tail cloud) Cumulonimbus incus (inc) Cumulonimbus murus ((mur) Wall cloud)
Cb-only accessories and other	Cumulonimbus flumen ((Cb flu) Beaver tail) Overshooting top Hot tower

Cumulus (Cu)
Variable vertical extent

Species	Fractus Cumulus humilis (Cu hum) Cumulus mediocris (Cu med) (Cumulus congestus (Cu con) (Cumulus castellanus (unofficial alternative name for Cu con)) (ICAO term for Cu con and "Cu cas" is Towering cumulus [Tcu]))
Other	Horseshoe Trade wind cumulus

Stratus (St)

Species	Stratus fractus (St fra) Stratus nebulosus (St neb)
St-only genitus cloud and other	Stratus silvagenitus (St sil) Fog (Fg) Surface level

Stratocumulus (Sc)

Species	Stratocumulus castellanus (Sc cas) Stratocumulus floccus (Sc flo) Stratocumulus lenticularis (Sc len) Stratocumulus stratiformis (Sc str) Stratocumulus Undulatus Stratocumulus volutus (Sc vol)

Low-level-only
supplementary features

Arcus ((arc) Shelf)
Tuba ((tub) Funnel cloud)

Low-level-only
accessory cloud and other

Pileus (pil)
Velum (vel)
Pannus (pan)
Other- Actinoform cloud (Stratocumulus)

Non-height
specific

Varieties	Duplicatus (du) Lacunosus (la) Opacus (op) Perlucidus (pe) Radiatus (ra) Translucidus (tr) Undulatus (un)
Supplementary features	Asperitas (asp) Cavum (cav) Fluctus (flu) Mamma (mam) Praecipitatio (pra) Virga (vir)
Mother clouds and human-made clouds	(Mother cloud)+genitus (e.g. cumulogenitus (cugen) (Mother cloud)+mutatus (e.g. cumulomutatus (cumut) Homogenitus (hogen) Homomutatus (homut)