MATTOON, Ill. – Just in time for July Fourth, a cloud formation that looked like something out the movie Independence Day filled the skies of central Illinois on Thursday in the moments before a derecho blasted the region with ferocious winds.
The formation, known as a “shelf cloud” typically notes the front edge of an approaching line of strong thunderstorms.
In Thursday’s case, the shelf cloud was signaling the arrival of a derecho that would go on to bring 80-100-mph wind gusts amid torrential rains and frequent lightning to the mid-Mississippi and Ohio valleys. Over 500,000 people lost power.
Shelf clouds are not tornadoes, but they can be indicative of intense thunderstorms with damaging winds.
As rain-cooled air rushes downward out of the thunderstorms – known as a downdraft – warm air is lifted upward out ahead of the storms to replace that cooler air.
When that warm air rises, it condenses and forms the shelf cloud that we all rush outside to snap a photo of for social media.
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Just don’t stay outside too long because that rain and wind come in fast.
A similar meteorological setup was in place in nearly the same area on Saturday afternoon and evening, meaning shelf clouds may be spotted again. You can always share your “shelfies” with us anytime, anywhere, in our America’s Weather Watchers community on Facebook, email them to [email protected] or add the hashtag #FOXWeather to your post on your favorite social media platform.