By the CNN Wire Staff
(CNN) - At long last, a cold front will snap a stubborn heat wave that has roasted much of the country for more than a week.
The front is expected to move through the Midwest and Northeast on Sunday after bringing some relief to the Upper Midwest and Great Lakes, according to the National Weather Service.
Chicago, for example, should enjoy a temperature of about 82 degrees by late Sunday afternoon -- down from 100 degrees earlier in the weekend.
The cold front will continue moving south through Monday and Tuesday, CNN meteorologist Alexandra Steele said.
The heat wave has left scores dead and hundreds of thousands without power.
But the cooler temperatures Sunday come with a catch. The cold front is expected to carry damaging storms, with large hail and strong winds, Steele said.
She predicted a long, hot summer for the country.
"Heat begets heat," Steele said.
Sizzling temperatures baked parts of the Midwest on Saturday, with St. Louis marking its 10th consecutive day of 100 degrees and higher.
Saturday's high of 107 in St. Louis broke a 103-degree mark set in 1936, said Butch Dye, hydrometeorologist technician for the National Weather Service.
Sunday's high temperature was expected to reach the lower to mid-90s, and Monday's expected 89 will match the normal high, said Dye.
Temperatures topped 100 degrees Saturday in a swath stretching from south-central Iowa to the Chicago area to Louisville, Kentucky, to Virginia, the weather service said.
Saturday's highs included 106 in Louisville; 105 in Lexington, Kentucky; 104 in Richmond, Virginia; 104 in Nashville, Tennessee; and 101 in Reading, Pennsylvania.
A 4-month-old girl in Greenfield, Indiana, died after being left in a car for an "extended period of time," police Chief John Jester said. While it wasn't clear how hot it had been inside the car, temperatures in that community of 20,000 people reached 103 degrees.
The baby's grandfather found the young girl and rushed her to the hospital, where she was pronounced dead. Her father, Joshua Stryzinski, was later arrested and charged with neglect of a dependent, resulting in death. Jester said that charge may change after detectives meet with prosecutors.
About 25 miles northwest, in the town of Fishers, Meg E. Trueblood was arrested for felony neglect of a dependent after her 16-month-old unattended daughter was pulled from a car at a shopping center, police said.
The toddler was rushed to the hospital in critical condition, said police spokesman Tom Weger. The temperature inside the vehicle was 124 degrees, said Weger, adding the baby was inside it for about one hour. An officer broke a window to reach the little girl.
The heat wave is leaving a significant mark: Nationwide, there have been more than 4,500 daily record highs in the last 30 days, according to the National Climatic Data Center. Also, the heat has brought nearly 240 all-time record highs between June 23 and July 5, Steele said Saturday.
Meanwhile, about 322,000 customers across 12 states and the District of Columbia suffered Saturday in the heat without the benefits of electricity, including power for their air conditioning and for refrigeration to keep their food edible.
Because utilities typically define each residential and business account as a customer, the actual number of people affected was not clear.
Many of these people have gone without power for a full week, thanks to strong storms fueled by the heat that barreled east from Indiana to New Jersey. Others have watched more recent but similar storms leave them in the dark.
The hardest-hit state continues to be West Virginia, where about 116,000 customers had no power Saturday.
Residents have been stocking up on ice to try to save food from spoiling in their useless refrigerators to the point that stores have sold out of it, CNN affiliate WSAZ reported.
Roger Harrah said he traveled from county to county, some 60 miles, searching for ice Friday and finally found a store with some.
"I thought I better get some while I can," Harrah said. "I tell you what, it is rough living without ice."
The extreme heat has also damaged roads.
Wisconsin received about 30 reports of roads buckling Thursday, according to transportation officials. Earlier this week, a viral video showed an SUV airborne after hitting a patch of buckled Wisconsin highway. Missouri has also warned drivers to be on the look-out for pavement buckling from heat.
CNN's Michael Martinez, Phil Gast, Maggie Schneider and Monica O'Connor contributed to this report.