More than 500,000 customers are still without power Monday afternoon, after the most damaging storm system in more than a decade roared through northern Illinois this morning, leaving downed trees and debris in its wake.

The severe storms packed winds as high as 80 mph and wreaked havoc on the morning commute. As of  5 p.m. Monday, Commonwealth Edison Co. reported that crews were still out trying to get the power back on for 541,000 customers. The heaviest reported outages were in the northern suburbs. 

“It has to do with downed power lines and other damage to our equipment. You know, this storm in particular brought with it some heavy rains, high winds and lots of lightening that struck our equipment and also, you know, struck trees that fell on our power lines, causing them to go down,” said Tony Hernandez with ComEd.

He also said that ComEd is hiring private contractors and workers from other states to help clean up.

The electric company said the storm system has affected at least 852,000 customers in all, though many have had their power turned back on. That makes it the most destructive storm since 1998.

The combination of power outages and high temperatures has city of Chicago officials working to prevent heat-related illnesses for people without air conditioning. Chicago Fire Department spokesman Larry Langford says the city has received calls about outages from about a dozen buildings housing seniors, who are most at-risk during hot spells.

“In the upper floors of these buildings, it’s not unusual, if you have 90 degrees of outside temperature, for the inside temperature in some of these buildings to rise well over 100 degrees,” Langford said, adding that some buildings could be evacuated if the power remains out for too long and temperatures begin to climb.

Airlines at O’Hare International Airport were experiencing delays up to 90 minutes for in and outbound flights and canceled more than 200 flights, according to the Chicago Department of Aviation.

At Midway International, airlines report a few delays between 30-90 minutes for in and outbound flights, with minor cancellations.

Service to the CTA Yellow Line was restored at 9:40 a.m. after a power outage.  The Purple Line is experiencing delays, with service running on a single track. The Red Line was experiencing delays with debris on the elevated tracks that has since been cleared.  The CTA had put shuttle buses in place at the time.

Metra saw major closures Monday morning as well. The Union Pacific North, Union Pacific Northwest and Union Pacific West lines were shut down for several hours Monday morning because of high winds. All three lines went back into service around 9 a.m., but significant travel delays persist on all three lines.

The Chicago region will most likely be spared from another round of heavy storms, according to National Weather Service forecasts. But heat index values are expected to climb above 100 degrees Monday afternoon.

“The main story is gonna be the humidity values,” said meteorologist Kevin Birk. “We’ve got very high humidity values. And because of that, it’s gonna make the temperature feel very warm.”

Temperatures are expected to drop into the 70s Monday night, with normal highs returning Tuesday.

The city of Chicago’s Department of Family and Support Services is asking people to check on seniors, and to call 311 if they have a neighbor who needs help.

Department spokeswoman Anne Sheahan says use of the city’s six cooling centers Monday was light for a hot day. She says 32 people had arrived by 4 p.m.

Natasha Payton and 93-year-old grandfather appreciated the one in East Garfield Park.

“We used to have the air conditioner running,” Payton said Monday afternoon. “But nothing is on because the power [has been] out since 8:30 this morning. It’s stifling hot in the house.”

Sheahan says use of the cooling centers could be heavier Tuesday if ComEd has not restored electricity to most of the Chicago homes without it.