Cloud atlas
The ten genera, fifteen species and nine varieties of the WMO International Cloud Atlas, with symbols and abbreviations.
How the system works
Genus, species, variety — a Linnaean scheme borrowed for the sky.
The modern scheme descends directly from the classification proposed by Luke Howard in 1802, whose Latin names — cirrus, cumulus, stratus and nimbus — remain the backbone of the WMO International Cloud Atlas today.
Every cloud belongs to exactly one of ten genera and, at most, one species describing its shape and internal structure. It may then carry several varieties describing transparency and arrangement, plus supplementary features and accessory clouds. A full name reads like Stratocumulus stratiformis perlucidus undulatus — Sc str pe un.
Cumulus and cumulonimbus are listed here with the low-level clouds: their bases sit in the low level even though they may grow through the medium and high levels.
Low level — family tree
Surface–2,000 m (0–6,500 ft). Tap a level above to switch; tap any name to read its entry.
- Stratus (St)
A uniform grey layer with a low, often ragged base; fog that does not touch the ground.
- Stratocumulus (Sc)
Grey or whitish patches of rounded masses or rolls, elements wider than five degrees.
- Cumulonimbus (Cb)
A dense, towering storm cloud with a fibrous or striated upper part, often anvil-shaped.