Fallstreak hole /hole punch cloud over Novokosino, Moscow, Russia.
Fallstreak holes are cloud formations that occurs as gaps in mid or high level cloud layers with trails of ice crystals dangling below. In order for a fallstreak hole to form, the cloud layer must be composed of supercooled droplets (liquid water), despite the temperatures at cloud level being well below 0°C. When one region of the cloud begins to freeze, the fallstreak hole forms. This begins a chain reaction whereby all the moisture from the supercooled droplets in the nearby area is drawn in and joins the ice crystals. These then grow big enough to fall beneath the hole. Fallstreak holes have been known to reach 50 kilometres across just an hour after the hole began to form.