Science- An imposing, ominous shelf cloud was spotted in the skies above Chicago.
- The cloud is a sign of severe thunderstorms and you should take shelter if one is coming your way.
At 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.
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.
"If you can get yourself a strong thunderstorm or line of thunderstorms [shelf clouds] will develop. So pretty much anywhere from 50 degrees north or south of the equator," Wysocki told Insider.
If you see one of these apocalyptic-looking shelf clouds coming toward you, it's important to seek shelter, Wysocki said.
"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.
A video shared on Twitter shows a timelapse of the cloud passing over Chicago.
—Alex Fischman (@alex_fischman) April 5, 2023
The National Weather Service of Chicago said the area was experiencing severe weather threats throughout this morning, with strong winds and rains.
Derek Van Dam, a CNN meteorologist, tweeted that the "powerful" shelf cloud brought wind gusts of up to 60 mph to Chicago.
—Derek Van Dam (@VanDamCNN) April 5, 2023
Why shelf clouds look so ominous
Shelf clouds are just one of the many types of clouds involved with a thunderstorm, Wysocki said.
Put simply, they form when cool and warm air mix. But something very specific has to take place to form that giant, ominous arc across the sky.
It starts with a rain shaft that occurs when a downdraft of cool air funnels a large amount of rain into a small region. "As that rain falls, it evaporates, cooling the surrounding air," Wysocki said.
That cooler air sinks compared to the warmer air around it, thus feeding the downdraft and increasing wind speed.
Eventually, 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.
"So what ends up happening then is as the air hits the ground, it then has to rise back up, and as it rises back up it cools the air and forms this cloud in this arc shape [aka shelf cloud] and that is the leading edge or gust front of a thunderstorm."
So, bottom line: there's a lot of moving air going on in a shelf cloud and you do not want to be in that tumultuous windy mix when it passes over.
Chicago reported severe damage from strong winds on Wednesday as the thunderstorm tore through the city. Large spires were blown off the top of a Church and came crashing down on the sidewalk below, and tall trees toppled over. There are no reports of injuries at this time.