A neat cloud phenomenon was observed by a WANE 15 viewer in Roanoke Friday afternoon. It is a large ellipitcal disc of blue sky and it appears within the thin cloud cover. 

This type of cloud formation is known as a fallstreak hole or a hole punch cloud. This phenomenon can occur in altocumulus or cirrocumulus clouds. In this case, the clouds are cirrocumulus due to their height in the sky.

In terms of cloud types, “alto” refers to mid-level clouds and “cirrus” refers to high clouds. The cumulus portion represents a “puffy” appearance, so in this case we are cirrocumulus. 

The hole forms in the clouds when an area of super-cooled water droplets that are not yet frozen, quickly evaporate, leaving a blank patch of sky. This process can begin as aircraft pass through the sky, introducing ice crystal formation by their motion. A small hole forms in the clouds and the rate of evaporation increases in an outward direction.

The result is an expanding hole in the cloud cover.