Cumulus castellanus
Cumulus castellanus low on the horizon
Appearance	Flat on the bottom, though has multiple "towers" on top
Precipitation	Usually, but not always

Cumulus castellanus (from Latin castellanus, castle) is an unofficial name of a species of cumulus cloud that is distinctive because it displays multiple towers arising from its top, indicating significant vertical air movement. It is a misnomer for cumulus congestus and correspondingly can be an indicator of forthcoming showers and thunderstorms. The World Meteorological Organization and the American Meteorological Society do not recognize cumulus castellanus as a distinct species, but instead classify all towering cumulus clouds as Cumulus congestus.^[1]

References

^ International Cloud Atlas

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

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

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)