It was the deadliest natural disaster in Chicago history.
Twenty years ago this week, more than 700 people died as temperatures soared above 100 degrees for days.
And the city's slow response to the crisis resulted in sweeping changes in the way we now deal with weather emergencies.
It was the middle of July in 1995, and for days temperatures hovered between the high 90's and low 100's, topping out at 106 degrees.
But no one initially realized the seriousness of the situation, and then-Mayor Richard M. Daley seemed to shrug it off.
"It's hot. It's hot out there. We all walk out there. It's very very very very hot," Daley had said.
But on the Saturday the heat finally broke, which was exactly 20 years ago today, FOX 32 went to the Cook County Medical Examiner's office and found dozens of police wagons and hearses dropping off multiple dead bodies.
Refrigerated trucks were brought in to handle the overflow.
Cook County’s Medical Examiner seemed in shock when FOX 32 asked him what was happening.
FOX 32: Have you ever seen anything like this before?
"I've never seen it. We're in the midst of a heat-related disaster here," Dr. Edmund Donoghue had said.
"Well it was one of the busiest days of my life," Dr. Donoghue told FOX 32 on Wednesday.
Dr. Donoghue now works in Georgia, and told FOX 32 via Skype that many of the victims had fallen through society's cracks.
"They were elderly people for the most part who lived alone, and the common unifying thread was they didn't have access to air conditioning," he said.
Making all of it worse, power outages affected thousands of people. Also, there was a lack of city resources because there was only a handful of cooling centers, which were poorly publicized.
"It was horrific to say the least," said Former 28th Alderman Ed Smith.
Smith said the slow-motion tragedy led to significant city reforms.
"As a result, because of what happened then the planning was done and now we're ready for those kinds of situations," Smith said.
Chicago’s Office of Emergency Management opened its new center shortly after the heat wave, and the city added a 311 service to better track patterns and problems.
The 1995 heat wave has also become one of the most studied natural disasters in U.S. history, with several books and dozens of academic papers on the subject all aimed at making sure we're never blindsided by the heat again.