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Thursday, race officials talked about lessons learned as they prepare for moderate heat during this year's marathon.
In the 30-year history of the Chicago Marathon, they've had a whole variety of weather, from snow and rain, to extreme cold, and of course extreme heat.
Last year was the first time that extreme heat has ever forced them to actually shut down the race. And that has prompted changes and concerns about the weather this year.
Marathon runners got their last few miles of training in Thursday afternoon before their 26-mile race on Sunday. Michelle Kuhr ran last year in the extreme heat and humidity and is hoping this year will be much different.
"It can't be as bad as it was last year, so by default it should be better. So, not worried about it all," said Kuhr.
A high temperature of 87 degrees combined with stifling humidity last year led marathon officials to stop the event after one runner died and more than 300 needed medical treatment.
The Chicago Area Runners Association operates the largest local marathon training program. They're advising runners to make sure they're prepared this year.
"People have run all summer in heat and humidity. So it shouldn't be too unusual. Just pinning a number on your jersey to run in a race does not remove from you responsibility to take care of yourself," said Dan Daly, CARA board president.
ABC7 meteorologist Mike Caplan says conditions should be better this year than last, although still uncomfortably warm for marathon runners.
"The main differentiation between this year's 80 degree temperatures for the race and last year's, there will be two. One, it will not be as hot. And the second distinction will be it will be nowhere near as humid as it was last year," said Caplan.
Marathon officials have made a number of changes in response to last year's problems, including dramatically increasing the amount of fluids on the course, and instituting a color-coded alert system to warn runners of weather risks.
Mike Caplan says the temperature in Grant Park at the start of the race on Sunday should be in the low 60s. It may get to the low 80s by mid-afternoon, but by that time, most runners should be finished.
You can read much more about the marathon on John Garcia's Running News Guy blog.