Residents of the Upper Midwest grabbed their cameras this past weekend as giant holes opened up in the clouds overhead.
The unusual formations, known as hole punch clouds, occur within a thin layer of clouds called altocumulus. Typically the holes develop when an airplane passes through the cloud layer, causing pressure changes that force supercooled water droplets in the clouds to turn into ice crystals. Those ice crystals then fall out and leave a clear void behind.
(MORE: What Punched a Hole in These Clouds?)
Several of these hole punch clouds were sighted across western Wisconsin and portions of Minnesota and Iowa on Friday and Saturday.
Some of the formations, such as the one below, were accompanied by fallstreaks, visible strands of ice crystals sinking out from the hole in the altocumulus cloud deck.
The National Weather Service in La Crosse, Wisconsin, posted a satellite photo showing how these formations looked from above. Notice the narrow white lines near the right (eastern) edge of the image – probably contrails from aircraft.
Here are some more images of the hole-punch clouds posted to social media. Most of them were taken in the La Crosse area. We're not sure the people in the first photo even noticed what was in the background ...
MORE ON WEATHER.COM: More Hole-Punch Clouds
