• Learn how to identify cloud types by using the flow chart from the International Cloud Atlas. Clouds are divided into 10 basic types (genera), depending on their general form.

    10 basic cloud types

    Cumulonimbus (Cb)

    Huge cloud tower, sometimes with anvil. Possible thunderstorm.

    Cirrus (Ci)

    Hooks, feathers, bands or patches with silky shimmer.

    Cirrostratus (Cs)

    Transparent milky or brous veil; casts shadow, produces halo.

    Cirrocumulus (Cc)

    Thin, pure white elds of small grains or ripples at a high level. Size < 1°

    Altostratus (As)

    Smooth, extensive layer; casts no shadow, even if Sun/Moon is recognizable as a blurred dot.

    Altocumulus (Ac)

    White/grey patches (turreted, lens shaped or balls of cotton), sheets or structured layer with undulations or rolls. Size 1° – 3°

    Nimbostratus (Ns)

    Dark rain cloud or bright snow cloud. Usually continuous rain, snow or ice pellets.

    Cumulus (Cu)

    Isolated, pu y cloud with sharp outlines.

    Stratus (St)

    Grey-whitish low layer, sometimes with drizzle or snow grains. If Sun/Moon is visible, its outline is clear. Can occur in fragments.

    Cumulonimbus (Cb)

    Huge cloud tower, sometimes with anvil. Possible thunderstorm.

    Stratocumulus (Sc)

    Grey or whitish elds, rolls or bundles, with rounded edges, at low level; regularly arranged elements. Size 5° – 10° (full hand)

    The genera are then further subdivided based on a cloud’s particular shape, structure and transparency; the arrangement of its elements; the presence of any accessory or dependent clouds; and how it was formed.


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