After the South Coast was treated to a spectacular sunrise thanks to a layer of altocumulus clouds over the region Monday, many residents also witnessed strange holes in the sky later in the day.
They’re called “fallstreak holes,” and they only happen in a nice layer of altocumulus or cirrostratus clouds.
They’re caused by areas in the clouds where the water has dropped below freezing but hasn’t yet frozen into ice crystals.
This water is said to be in a supercooled state. The reason it hasn’t frozen is a lack of “ice nuclei” — tiny particles onto which ice crystals can begin to form.
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But once just one ice crystal forms, a domino effect called the Bergeron Process takes place, and all of the supercooled droplets freeze quickly.
These ice crystals then fall, creating the wispy part of the fallstreak hole. But they aren’t able to fall very far. They melt and evaporate quite quickly.
The hole is formed by both the loss of water in the cloud by ice crystals falling and another result of the Bergeron Process which causes the rest of the water in the cloud to evaporate.
The holes were spotted in areas of southwestern B.C. such as Abbotsford, Comox, Sidney, Nanaimo, Maple Ridge and Langley.
It seems planes can kick off the Bergeron Process by adding ice crystals to the area of supercooled water in the cloud.
Notice some of the fallstreak holes are elongated as if a plane travelled in the cloud layer for a distance.
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