Description

Pannus (from the Greek word meaning "shred"), or scud clouds, is a type of fractus cloud at low height above ground, detached, and of irregular form. It is technically called an accessory cloud because it is always found beneath another cloud, such as nimbostratus or cumulonimbus clouds. These clouds are often ragged or wispy in appearance.

When occurring under nimbostratus, pannus clouds are typically associated with precipitation, appear darker than the cloud layer above them, and often move quickly.

For cumulonimbus, when caught in the outflow (downdraft) beneath a thunderstorm, scud clouds will often move faster than the storm clouds themselves. When in an inflow (updraft) area, scud clouds tend to rise and may exhibit lateral movement ranging from very little to substantial.