Dangerous heat to head to Northeast after slamming Midwest

Extreme heat is gripping the Midwest before moving into the Northeast.

Chicago is in the center of an excessive heat warning that stretches north to Madison, Wisconsin, and south to Springfield, Illinois.

The heat index -- what temperature it feels like with humidity -- soared to a scorching 115 degrees in Chicago on Tuesday. Chicago's actual temperature hit 99 degrees, breaking the city's daily record of 97 degrees.

In Detroit, public school students were released three hours early on Tuesday due to the heat.

Next, the dangerous temperatures will move east.

On Wednesday, the heat index is forecast to climb to 104 degrees in Nashville, Tennessee; 100 degrees in Indianapolis; 105 in Philadelphia; and 103 in Washington, D.C.

D.C. may hit a new record-high actual temperature of 100 degrees.

By Thursday, the Northeast will cool down. But temperatures will stay in the 90s in the South as the week ends.

There are hundreds of deaths each year in the U.S. due to excessive heat, according to CDC WONDER, an online database, and scientists caution that the actual number of heat-related deaths is likely higher.

Last year marked the most heat-related deaths in the U.S. on record, according to JAMA, a peer-reviewed medical journal published by the American Medical Association.

Click here for tips on how to stay safe in the heat.