Puzzled residents of Southern Finland gazing at the skies on Wednesday morning may have noticed a large, uncommon patch of blue in the middle of a thin mass of cloud. The phenomenon, known as a fallstreak hole or skypunch, gained immediate traction as users posted numerous images of the striking gap on social media.
Fallstreak holes are formed when supercooled water in the clouds reaches temperatures below 0 degrees Celsius, but does not freeze. Forming ice crystals cause water droplets around them to evaporate, causing a circular or elliptical hole. Aeroplanes passing through clouds have been known to cause cloud holes.
Yle meteorologist Seija Paasonen observed the momentary skypunch around 8 am.
"After about ten minutes, some thin, high clouds began to cover the gap. At about 8:20 am the hole was almost covered up," she says.
Paasonen estimates that the fallstreak hole occurred at an altitude of some 6-8 kilometres.
So-called holepunch clouds are not exactly uncommon, the meteorologist says, but still rare as the phenomenon only occurs a few times a year.
What made this hole special was its symmetrical, uniform shape.
"This is the most beautiful one I've ever seen," Paasonen says.