What is a skypunch and why does it happen?

Fallstreak holl

If you live in Ontario, you may have noticed something strange happening in the sky recently. In mid-February, incredible cloud formations appeared over Scarborough—though it’s the places where the clouds weren’t that were most notable. Giant holes appeared in the sheets of clouds overhead, looking like someone or something had come and scooped them away.

Skypunch over Scarborough
Photo courtesy of The Weather Network
A still from a video taken of the skypunch over Scarborough recently.

People often mistake this phenomenon for UFO activity, but it’s actually a perfectly natural occurrence. It’s called skypunch, and it only happens when a number of weather factors align just so.

So how do these massive holes come to be?

Skypunch (also known as fallstreak holes) happens as a result of something called the Bergeron Process. But to understand the Bergeron Process, first we have to understand clouds themselves. Clouds are made of vapour, which is basically a collection of half-condensed water droplets in the air. In order for the Bergeron Process to occur, the water droplets in the clouds need to be at a temperature below zero without becoming ice or snow. In certain pressure conditions, the cloud droplets have nothing to adhere to, and so they cannot freeze the way water normally does. Instead, they remain suspended in the form of supercooled water droplets.

However, once some of the vapour does turn into ice, it gives all the other supercooled water droplets something to adhere to, and all at once, a large portion of the cloud freezes in a large chain reaction. Much of the vapour turns into ice crystals, while the rest evaporates immediately, leaving a huge hole in the cloud.

The physical process is a bit complicated, but it’s easy to appreciate the results. Skypunch is a fascinating occurrence, and it only happens when conditions are just right.

You can view the full video of the skypunch over Scarborough at The Weather Network.