Cloud atlas

The ten genera, fifteen species and nine varieties of the WMO International Cloud Atlas, with symbols and abbreviations.

Supplementary features

Attached formations and precipitation structures.

incanvil

The smooth, fibrous anvil spread out at the top of a cumulonimbus at the tropopause.

Applies toCb

mamudder

Hanging pouches on the underside of a cloud, most striking beneath an anvil.

Applies toCi Cc Ac As Sc Cb

virrod, streak

Trails of precipitation that evaporate before reaching the ground.

Applies toCc Ac As Ns Sc Cu Cb

praprecipitation

Precipitation that does reach the ground.

Applies toAs Ns Sc St Cu Cb

arcarch

A dense horizontal roll with ragged edges along the leading gust front of a storm.

Applies toCu Cb

asproughness

Chaotic, wave-like undulations on the cloud base, as if viewed from beneath a rough sea surface. Added to the Atlas in 2017.

Applies toAc Sc

tubtrumpet

A rotating column or cone hanging from the base — a funnel cloud.

Applies toCu Cb

fluwave

Short-lived breaking-wave curls along the top of a layer (Kelvin–Helmholtz billows).

Applies toCi Ac Sc St Cu

murwall

A localised lowering of the storm base beneath the rain-free area — the wall cloud.

Applies toCb

cautail

A horizontal tail cloud attached to the wall cloud, extending toward the precipitation core.

Applies toCb

cavhole

A circular or linear hole punched through a supercooled layer, usually with virga in the middle — a fallstreak hole.

Applies toCc Ac Sc