What is a holepunch cloud?

ALLISTER AALDERS weather@saltwire.com @allistercanada Allister Aalders is the weather specialist for the SaltWire Network, providing forecasts and analysis for Atlantic Canada. #AskAllister



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When you look up at the clouds, you never know what exciting shapes or formations you might find. Some formations are more interesting and uncommon than others. Matt McKinnon captured a more unusual one recently in Glen Haven, N.S. He shared this photo of a hole in the cloud deck and wondered what might have caused it. The cloud formation Matt captured is what’s known as a fallstreak hole, also known as a holepunch cloud. Fallstreak hole clouds form in the mid-to-high levels of our atmosphere, most commonly in altocumulus or cirrocumulus clouds. These clouds are made up of tiny, supercooled water droplets – meaning the droplets are below the freezing mark but not yet frozen. When aircraft pass through or travel near this type of cloud deck, the condensation trail from the aircraft introduces ice crystals. This causes the supercooled water droplets to freeze and form ice crystals. These ice crystals then begin to fall from the sky but evaporate before reaching the ground – leaving a large circular or elliptical hole in the sky with some evaporative clouds in the middle, resembling a holepunch. You might think these clouds are common with aircraft coming and going all the time. However, fallstreak holes are quite uncommon as you need all the right ingredients to be in place simultaneously for one to form. So, if you ever see what looks like a hole in the sky, no, it’s not a UFO. It’s a fallstreak hole or holepunch cloud. Thank you to Matt for capturing the fantastic fallstreak photo and for his #AskAllister question.