Accessory cloud

They are associated with deep moist convection and especially cumulonimbus, the primary cloud producing thunderstorms.

The pileus and mammatus types can form at various altitude ranges depending on the main clouds with which they are associated.

The World Meteorological Organization classifies most accessory clouds as supplementary features.

The height range classification of a supplementary feature is the same as the parent cloud.

As an example, the anvil cloud (supplementary feature incus) forms at high altitude but is not classified by the WMO as a high cloud because of its association with the genus cumulonimbus.