Wiktionary
n. Sub grouping of standard cloud classification system, coming after the major cloud genera
Wikipedia
Cloud species are a set of fourteen terms used to describe the shape and structure of clouds. Each one has its name abbreviated to a three letter term.
Species
Abbreviation
Description
Genera
Calvus
cal
Tops of clouds lose hard, rough appearance and become smooth
Cb
Capillatus
cap
Tops of clouds become distinctly fibrous or striated. Cirrus clouds are often in appearance
Cb
Castellanus
cas
Distinct turrets rising from a large base or line of cloud
Sc, Ac, Cc
Congestus
con
Great vertical height much larger than the base, shows vigorous growth with cauliflower like tops
Cu
Fibratus
fib
Fibrous appearance, with straight or uniform curves and no distinct hooks
Ci, Cs
Floccus
flo
Individual tufts of clouds with ragged bases and often with noticeable virga
Ac, Cc, Ci
Fractus
fra
Broken cloud with ragged bases and edges
Cu, St
Humilis
hum
Cloud with limited vertical height with a length much bigger than their height
Cu
Lenticularis
len
Lens or almond shaped clouds that are stationary in the sky
Sc, Ac, Cc
Mediocris
med
Clouds of moderate height that are around equal height and length, growing upwards
Cu
Nebulosus
neb
Featureless sheet of cloud with no structure
St, Cs
Spissatus
spi
Dense cloud appearing lighter shade of grey when viewed toward the sun
Ci
Stratiformis
str
Cloud in an extensive sheet or layer
Sc, Ac, Cc
Uncinus
unc
Distinctly hooked usually without a visible head
Ci