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What were they? Crazy clouds over Greensboro Sunday

They're called "hole punch clouds" or officially, fallstreak holes

GREENSBORO, N.C. — Did you see these odd-looking clouds over the weekend? As a ribbon of clouds filtered into the Triad through the morning and afternoon more than a few of these "hole punch" or "falling streak" clouds could be seen. 

They're pretty neat to see but the conditions have to be just right for them to form. So how does it happen? Believe or not, airplanes can make them form.

It starts with water droplets, which form clouds.

Credit: WFMY
Supercooled water droplets are needed to form hole punch clouds

These water droplets are "supercooled" meaning they're below freezing but they're not yet frozen. In order for water to freeze it has to have something to freeze onto. Scientists call this a condensation nuclei. That can be something like sand or dust particles but in this situation, it's exhaust from jet engines.

Credit: WFMY
Tiny particles from airplane exhaust can create ice crystals which get heavy, and fall from the cloud

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As airplanes pass overhead through the clouds those supercooled water droplets now have something to freeze on. They freeze around the exhaust particles, crystallizing and falling creating those "streaks" that you see falling down.

They were easily seen on camera this past Sunday. Debra Marshall in Burlington took this shot early in the afternoon and sent it to the WFMY Weather Team.

Credit: Debra Marshall

Once the water droplets freeze, they fall because they're heavy...of course, this is gravity taking a toll on them. But once there are enough of those exhaust particles to freeze on, it starts to create a chain reaction. As the water droplets around the frozen crystals evaporate, the big "hole punch" is formed.

Credit: WFMY

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