Extreme Heat Warning now in effect for area through Thursday

An Extreme Heat Warning is in effect for the Chicago area through Thursday night as hot, humid air is expected to linger longer than initially forecast.

Heat index values were expected to climb as high as 110 degrees in some areas Tuesday, but meteorologists at the National Weather Service bureau in Romeoville warn Wednesday’s conditions could be worse.

“There’s probably going to be less cloud cover, which has the potential for higher temperatures,” said Ricky Castro, a weather service meteorologist.

After issuing a heat advisory Monday, Castro said the Extreme Heat Warning was issued because the heat index values are expected to exceed 105 degrees for a prolonged period.

But despite how warm it feels, Castro doesn’t expect any temperature records to be broken. Most heat records this week are in the triple digits, he said.

While Monday saw heat index values climb to 105 degrees or more in places like Joliet and Waukegan, according to weather service data, high temperatures were only in the low 90s.

Additionally, hazy skies moved over much of Illinois Tuesday thanks to the jet stream that is pulling warm, humid air up from the Gulf and bringing “Saharan Dust” from Africa along with it.

The dust is not uncommon this time of year, Castro said. It’s high enough in the atmosphere that it won’t affect breathing. It can make sunrises and sunsets more colorful.

State officials are also urging anyone without access to air conditioning to go to any of the hundreds of cooling centers throughout the state. Most public buildings are operating as cooling centers during normal operating hours, but many police departments are opening their doors all day during the heat wave. A list of cooling centers is available at keepcool.illinois.gov.

They also urge residents who do have to venture outside during the heat wave to stay hydrated, apply sunscreen regularly, wear light, loose-fitting clothing, take frequent breaks in shaded areas or inside air-conditioned buildings, and limit activities during the hottest part of the day.

Meanwhile, festival organizers getting ready for Fourth of July celebrations are keeping an eye on weather conditions as well.

One of the suburbs’ largest summer festivals, Arlington Heights’ Frontier Days, kicks of its 50th year Wednesday amid high temperatures expected to reach the mid 90s and a heat index forecast to exceed 100 degrees between noon and 6 p.m.

Pat Peery, the president of the fest's board of directors, said measures will be in place to help festivalgoers beat the heat. That includes water at the entrance to the festival grounds, an air-conditioned shelter for people who feel overheated, plenty of tents cooled by fans and an on-duty nurse and first-aid station.

“And we got some good news today that temperatures will be in the 80s for Friday and the weekend, so much more comfortable during the day and even cooler at night for our entertainment,” Peery said. “We're looking forward to a big crowd.”

Palatine officials said organizers of Hometown Fest, which kicks off Thursday, are also taking precautions.

“Palatine police and fire personnel will closely monitor conditions throughout the event and work with event organizers to help ensure the safety of attendees, volunteers and staff,” said Hadley Skeffington, deputy village manager.

Daily Herald staff writers Charles Keeshan and Steve Zalusky contributed to this report.