Pileus

Definition

A supplementary cloud feature in the form of a cap or hood of cloud sitting directly above the top of a cumulus or cumulonimbus, looking like a small hat. It is thin, short-lived, and often only lasts a few minutes.

Field note

Pileus forms when the rapidly rising top of a cumulus pushes air above it upward, and that air cools and condenses. Seeing a pileus means the updraught is punching into a stable layer, which means the convection is strong.

Related terms

• Congestus · congestus
• Cumulonimbus · Cumulonimbus
• Incus · incus