Punch hole clouds, also known as fallstreak hole are large circular clearings that can appear in cirrocumulus or altocumulus clouds. 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.
Because of their rarity and unusual appearance, fallstreak holes are often mistaken for or attributed to UFOs. It is only during the last decade the cause of formation of these clouds has been somewhat understood.
It is believed that a disruption in the stability of the cloud layer, such as that caused by a passing jet, may induce the domino process of evaporation which creates the hole. Such clouds are not unique to any one geographic area and have been photographed from the United States to Russia