SAN FRANCISCO (KRON) – An unusual cloud formation has Bay Area residents puzzled Friday afternoon.

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Several viewers reached out to KRON4 to ask what the giant hole in the sky was.

The phenomenon was seen mainly on the Peninsula in cities like San Bruno, San Mateo, and Burlingame.

But residents in the East Bay also tell us they saw the clouds.

KRON4 Chief Meteorologist Lawrence Karnow says the formation is known as a “fallstreak hole” or “hole punch cloud.”

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The clouds form when there are water droplets that are colder than freezing but have yet to freeze, according to the National Weather Service.

These “supercooled” water droplets need a “reason” to freeze, which usually comes in the form of ice crystals, the NWS explains.

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Planes passing through the cloud layer can bring these ice crystals.

Once the ice crystals are introduced, the water droplet quickly freeze, grow and start to fall. A hole is left behind, which will start to expand outward as neighboring droplets start to freeze.

 

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