If you are a frequent cloud observer, have you ever noticed that cumulus clouds may sometimes possess atypical "hairstyle" on its top with a smooth and shining appearance? This type of accessory cloud is called "pileus cloud".

Persistent strong updrafts usually occur within growing cumulus or cumulonimbus. When there is a stable and moist airstream flowing above the cloud top, the airstream will be pushed upward leading to condensation and formation of a cap cloud aloft called "pileus cloud". However, this atypical "hairstyle" does not last long. The cap will eventually be cut through when the cumulus cloud beneath continues to grow upward.