Smoldering heat forced Chicago Marathon officials to make an historic decision Sunday: they shut down the course midway through the race due to the dangerous hot weather.
At least one runner died during the race, and hundreds more had to be treated at hospitals after collapsing along the route.
Temperatures on the marathon course reached 90 degrees, making it the hottest Chicago Marathon in history. With water and energy drinks in short supply, race organizers closed the course about four hours into the race, and diverted runners from the race route back to the starting area.
Race officials say 45,000 people signed up to race, but nearly 10,000 of them never finished.
Chad Schieber, 35, of Midland, Mich., collapsed during the race and was pronounced dead at a veteran's affairs hospital. An autopsy was scheduled for Monday.
"Obviously very sad news, and our thoughts and prayers are with the individual's family," said Shawn Platt, senior vice president of LaSalle Bank, the marathon's sponsor.
Race officials say 312 others went to area hospitals for treatment.
"This is October — this is why we staged the event in October — because of the cool weather," said race organizer Carey Pinkowski. "If you remember last year, we were dealing with hypothermia. So it's just a very strange day."
Chicago isn't the only place dealing with the stifling heat.
Forecasters say a high pressure system, parked over the Ohio Valley, is causing intense heat across much of the country. Another factor: the air is already dry in many places, because of a massive drought across entire regions of the U.S.
At Lake Altoona, one of the major water sources for the city of Atlanta, drought has already left water levels 12 feet below normal. And if it continues, lake levels could fall another foot per week.
"If the lake continues to fall, it will be a concern that we all conserve water, so we'll all have water, to take our showers, use the toilets and have drinking water," said Michael Lapina with the Army Corps of Engineers.
While some enjoy the unseasonable heat, forecasters say normal October temperatures will likely return to much of the U.S. later this week.