Pannus

Definition

A supplementary cloud feature consisting of ragged shreds of cloud in a more or less continuous layer, occurring below another cloud and separated from it. It is the same thing observers often call scud.

Field note

Pannus below a dark, thickening cloud base means rain is 30 to 60 minutes away. It forms when the air just below the base is being moistened by falling precipitation and lifted by the outflow.

Related terms

• Altostratus · Altostratus
• Nimbostratus · Nimbostratus
• Fractus · fractus