The Midwest of the United States may get hit with a gigantic storm, says the National Weather Service. The service said 12 million people are at risk of severe weather.  

The biggest risk is in Illinois, Indiana and Ohio. There's less of a risk for an area extending from Wisconsin to Washington, DC. The storms may pack winds as high as 50 to 100mph.

These storms can also be referred to as "Derechos." What's makes a "derecho" is that while normal thunderstorms have damaging winds a mile or two wide and a few miles long, derechos can have damaging winds tens of miles wide, and hundreds of miles long.

According to NOAA, the Weather Service's parent agency, a storm qualifies as a derecho is "if the wind damage swath extends more than 240 miles (about 400 kilometers) and includes wind gusts of at least 58 mph (93 km/h) or greater along most of its length."

According to CBS News, the risk of severe weather in Chicago, Indianapolis, Cincinnati and Columbus, Ohio, is roughly 45 times higher than on a normal June day, Bunting said. Detroit, Baltimore, Washington, Milwaukee, Pittsburgh and Louisville, Ky., have a risk level 15 times more than normal. All told, the area the weather service considers to be under heightened risk of dangerous weather includes 64 million people in 10 states.

"It's a pretty high threat," Bunting said, who also warned that the storms will produce large hail and dangerous lightning. "We don't want to scare people, but we want them to be aware."

Wednesday "might be the worst severe weather outbreak for this part of the country for the year," said Jeff Masters, meteorology director at Weather Underground.