That cooler air sinks compared to the warmer air around it, thus feeding the downdraft and increasing wind speed.Įventually, that column of cold air hits Earth's surface where it 'spreads out into a circular shape.' Sort of like a ripple, when you drop a pebble in a pond, Wysocki said. 'As that rain falls, it evaporates, cooling the surrounding air,' Wysocki said. It starts with a rain shaft that occurs when a downdraft of cool air funnels a large amount of rain into a small region. But something very specific has to take place to form that giant, ominous arc across the sky. Put simply, they form when cool and warm air mix. Shelf clouds are just one of the many types of clouds involved with a thunderstorm, Wysocki said. Shelf clouds form an ominous looking arc across the sky and are a warning sign to seek shelter. 'You really should take shelter because once the cloud gets over you the winds pick up from like 0 mph to 45-70 mph in no time whatsoever,' Wysocki told Insider.Ī video shared on Twitter shows a timelapse of the cloud passing over Chicago. If you see one of these apocalyptic-looking shelf clouds coming toward you, it's important to seek shelter, Wysocki said.

So pretty much anywhere from 50 degrees north or south of the equator,' Wysocki told Insider. 'If you can get yourself a strong thunderstorm or line of thunderstorms will develop. In fact, shelf clouds are quite common and can develop just about anywhere there's a thunderstorm brewing, said Mark Wysocki, a senior lecturer at Cornell's Earth and Atmospheric Sciences Department and New York State climatologist.

Video shows the cloud moving through the city, bringing strong winds up to 60 mph with it.Īt first glance, the shelf cloud that passed through the skies of Chicago on Wednesday morning looked like something out of 'Independence Day.' But don't worry - this ominous-looking formation isn't signaling the end of the world. The cloud is a sign of severe thunderstorms and you should take shelter if one is coming your way. EarthcamĪn imposing, ominous shelf cloud was spotted in the skies above Chicago. A picture of a shelf cloud moving through downtown Chicago courtesy of EarthCam.

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