It's not the temperature that will get you today, but the heat index.
With temperatures projected to top out at 98 degrees at O'Hare International Airport this afternoon, the humidity will be exceptionally high, creating a feel like temperature of about 110 degrees, said Ben Deubelbeiss of the National Weather Service.
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The heat index is a table that records moisture in the atmosphere, he said. That moisture creates humidity, which makes it feel hotter than it really is.
He added there will be a slight westerly breeze of about 20 mph that could add some relief to people, but said the relief will only be minor.
"The best move is to just stay in the air-conditioning today," he said. "With the high dew points, humidity and the heat index, it's going to feel like 110 degrees."
It was 90 degrees with a heat index that made temperatures feel like 94 degrees at 10 a.m., Deubelbeiss said.
The National Weather Service has issued a heat advisory that will go into effect at noon today, he said, and last through 8 p.m. this evening.
He added there are slight chances that severe thunderstorms could pop up in isolated areas.
He said a cold front in the south is causing some isolated storms to form to the west. Those storms will be severe should they roll into Illinois.
"Any storms that arrive today will be strong and severe," he said. "But, any storm possibility is widely scattered and isolated."
In the meantime, authorities are asking people to stay indoors in air-conditioning as much as possible. People without air-conditioning are being told to go someplace with cool air, like a library, mall or one of many cooling centers available in many counties.
People are urged to wear sunscreen when outside, along with light colored clothes in order to reduce heat.
People are being told to drink plenty of water, even when not thirsty, and stay away from caffeine drinks and alcohol. Those beverages have a tendency to dehydrate people.
Also, motorists should not leave pets or children alone in a car today, avoid exertion between noon and 8 p.m. and to take a cool bath or shower if you become too hot.