Abbreviation Ac
Family B
Genus Altocumulus
Occurrence Worldwide
Altitude 2000-5000m
Formation Lifting of a large air mass followed by condensation combined with atmospheric instability
Precipitation Light rain if cloud is thick
Potential Hazards Ice accretion on aircraft; may signal approaching frontal system


Altocumulus castellanus
Altocumulus duplicatus
Altocumulus floccus
Altocumulus lacunosus
Altocumulus mackerel sky
Altocumulus opacus
Altocumulus perlucidus
Altocumulus radiatus
Altocumulus stratiformis
Altocumulus translucidus
Altocumulus undulatus
Altocumulus virga

High Clouds (Family A): Cirrus (Ci) • Cirrus aviaticus • Cirrus intortus • Cirrus radiatus • Cirrus uncinus • Cirrus Kelvin-Helmholtz • Cirrostratus (Cs) • Cirrocumulus (Cc) • Pileus • Contrail
Middle Clouds (Family B): Altostratus (As) • Altostratus undulatus • Altocumulus (Ac) • Altocumulus undulatus • Altocumulus mackerel sky • Altocumulus castellanus • Altocumulus lenticularis
Low Clouds (Family C): Stratus (St) • Orographic stratus • Fog • Nimbostratus (Ns) • Cumulus humilis (Cu) • Cumulus mediocris (Cu) • Stratocumulus (Sc)
Vertical Clouds (Family D): Cumulonimbus (Cb) • Cumulonimbus incus • Cumulonimbus calvus • Cumulonimbus with mammatus • Cumulus congestus • Cumulus castellanus • Pyrocumulus  • Pyrocumulonimbus