A fallstreak hole is a large circular gap, that can appear in 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 failure of ice nucleation. When ice crystals do form they will set off a chain reaction causing the water droplets around the ice crystals to evaporate leaving a large usually circular or elliptical hole.
H. Raab (User:Vesta), CC BY-SA 3.0, via Wikimedia Commons
Jtrombone, CC BY-SA 4.0, via Wikimedia Commons
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Beckachester, CC BY-SA 4.0, via Wikimedia Commons
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