Punch Hole Clouds
Punch hole clouds, also known as fallstreak hole, hole punch cloud, skypunch, canal cloud, cloud hole are large circular clearings that can appear in cirrocumulus or altocumulus clouds.
Hole Punch Clouds in Los Angeles
Hole Punch and Fallstreaks Over Paris
Hole punch cloud over Austria
Such holes are formed when the water temperature in the clouds is below freezing but the water has not frozen yet due to the lack of ice nucleation particles.
When a portion of the water does start to freeze it will set off a domino effect causing the water vapor around it to freeze and fall to the earth as well. This leaves a large, often circular, hole in the cloud.