CHICAGO/BOSTON The heat wave baking the country's mid-section entered its third day on Wednesday with high temperatures taking a deadly toll from Milwaukee to Memphis.
The hot, humid air, which the National Weather Service warned could create triple-digit heat index readings in many places, also began to spread into the northeast, where temperatures across Southern New England were expected to climb into the 90s on Wednesday and inch higher toward potentially historic numbers on Thursday, meteorologists said.
In Wisconsin, a 69-year-old resident of a Milwaukee nursing home was found dead Tuesday evening after being left unattended outside for three hours in the afternoon heat, which reached a record 97 degrees on Wednesday and hit 90 by early Wednesday afternoon.
The Milwaukee medical examiner is conducting an autopsy to determine if the extreme heat was a factor in the man's death, Karen Domagalski, the agency's operations manager, told Reuters.
In Tennessee, officials said a 75-year-old Memphis woman and a 60-year-old man in Brighton both died of the heat, which reached 98 on Tuesday and was 93 by early Wednesday afternoon.
The heat -- in the mid to upper-90s throughout Tennessee -- coincides with the kickoff of two massive music festivals that has officials in the state bracing for heat-related calls.
The CMA Music Festival kicks off on Wednesday with a parade in Nashville, but the big events begin Thursday, most of them outdoors at LP Field, the open-air home of the Tennessee Titans football team.
Meanwhile, about 85 miles southeast of Nashville, 80,000 fans are expected for Bonnaroo, the huge, four-day rock festival that takes place annually in former farm pastures in Manchester.
Fans are expected to jam up Interstate 24 as they begin arriving on Wednesday for the event, which begins Thursday. Heat has been a problem in the past, with one person collapsing and dying last year.
In Chicago, where temperatures this week hit a 34-year high and afternoon temperatures were expected to reach 95 on Wednesday, forecasters said relief was on the way with a cold front sweeping in tonight.
But while the front will push the hot weather eastward, and drop temperatures by as much as 30 degrees, it will also set the stage for severe and possibly damaging thunderstorms in Indiana, Illinois and Wisconsin.
In Maryland, where two people have died over the last two weeks as a result of heat exposure, temperatures in Baltimore broke existing record highs on Wednesday, according to AccuWeather.
The mercury in Newark, New Jersey also hit a new record high and temperatures in Washington, D.C., according to AccuWeather, and Allentown and Reading, Pennsylvania tied record highs, AccuWeather said.
Heat gauges in Philadelphia could near 100 degrees mid-week, challenging a record temperature for Thursday of 98 set in 1933.
Sticky heat prompted early dismissals and canceled after-school activities at some public schools in Philadelphia and throughout Connecticut.
Hot and humid weather was expected to stifle much of the Mid-Atlantic, said Greg Heavener, meteorologist with the National Weather Service in Mount Holly, New Jersey.
"It's going to be a really nasty couple of days," Heavener said.
In Boston, sweltering heat could break record temperatures set in 1984 but a cooling sea breeze off the water was likely to spare Cape Cod and the islands, said Charlie Foley, meteorologist with the National Weather Service in Taunton, Massachusetts.
Thunderstorms forecast for Thursday were expected to usher in significantly cooler temperatures on Friday.
Boston anticipated a dramatic cool down over the weekend with temperatures in the upper 60s.
(Additional reporting by Lauren Keiper in Boston and Tim Ghianni in Nashville)