CHICAGO — As the Chicagoland area prepares for severe weather on Friday, massive storms are brewing over at least 15 states in the Midwest and southern United States.

Meteorologists are urging people on Friday to brace for dangerous weather including tornadoes, saying the conditions are similar to those a week ago that unleashed a devastating twister that killed at least 21 people in Mississippi.

More than 85 million people were under weather advisories Friday as the National Weather Service’s Storm Prediction Center forecast an unusually large outbreak of thunderstorms with the potential to cause hail, damaging wind gusts and strong tornadoes that could move for long distances over the ground.

The area at greatest risk for storms on Friday follows a large stretch of the Mississippi River from Wisconsin all the way to Mississippi, with rare high-risk advisories centered around Memphis; and between Davenport, Iowa, and Quincy, Illinois and surrounding areas.

Forecasters issued tornado watches over both high-risk regions until Friday evening, with the weather service expecting numerous tornadoes and calling it a “particularly dangerous situation.”

All told, by Friday afternoon, tornado watches issued by the National Weather Service cover most of Missouri, Arkansas and Iowa; western Illinois; and parts of Wisconsin, Texas, Tennessee, Kentucky and Mississippi. Tornado warnings were issued for isolated areas of Arkansas, Missouri and Illinois on Friday afternoon.

In Iowa City, the University of Iowa canceled Friday’s watch party for fans who planned to gather for the women’s basketball Final Four game against South Carolina. Deputy Director of Athletics Matt Henderson said in a statement the decision was made “due to the unpredictable timing of possible severe weather and potential storm impact.”

Residents of central Iowa were warned to take shelter as severe thunderstorms carrying wind and hail moved over the region on Friday, the National Weather Service (NWS) said.

Kevin Cavallin posted the video above from the Iowa State University (ISU) campus on Friday afternoon, estimating the hail was approximately quarter-sized.

The NWS said multiple other severe storms capable of producing large hail were moving across the Des Moines area on Friday.

The Associated Press and Storyful contributed to this article.

Stay with WGN as this story develops.