It reached 105 degrees Fahrenheit in St. Louis.
It also hit the century mark in Chicago for the third day in a row, something that only happened previously in 1947 and 1911. The Chicago Tribune said the 103 degrees recorded at O'Hare International Airport broke the record of 99 degrees set in 1988. It's possible the city could see 100 degrees for a fourth straight day Saturday, which would be a first.
A cooling trend is on the way, however, National Weather Service meteorologist Brian Korte told USA Today.
"For the most part by Sunday it breaks across the Midwest and across most of the Northeast and mid-Atlantic region," Korte said. "By Sunday temperatures are dropping already across all of those areas."
USA Today reported Hill City, Kan., has had 13 days above 100 since June 23rd, St. Louis has had 13 and Indianapolis four. Washington, D.C., has had nine days in a row of 95 or hotter and it's expected to hit 100 Saturday.
"It's been an unusual event," Korte said of the deadly heat wave.
The National Climatic Data Center said nationwide, 4,230 daily heat records and 233 all-time heat records were broken in the past 30 day.
At least 11 heat-related deaths have been reported in Maryland, The Baltimore Sun said. Six deaths have been reported in the Chicago area and three in Rock County, Wis., CNN reported. Three more deaths were recorded in St. Louis, USA Today said.
Meanwhile, crews maneuvered through Great Smoky Mountains National Park in Tennessee, looking for any visitors stranded after a storm blew through the area, killing two people, downing trees and crushing cars, the Knoxville News Sentinel reported Friday.
Elsewhere, hundreds of thousands of residents in the nation's midsection and mid-Atlantic states were without power, with Friday expected to bring more triple-digit temperatures to areas still recovering from massive storms in late June.
Heat and extreme heat advisories were posted in multiple states.
Centers were set up in several West Virginia communities to provide breakfasts and dinners to residents still without power.
The storms that stretched from Indiana to New Jersey June 29 were blamed for 22 deaths. Three more people in North Carolina died in a another round of storms Sunday.
More than 549,000 customers had no power as of Thursday night in 11 states and the District of Columbia, officials said.
"We're starting to see light over the horizon; the only bad thing is the storms that we keep having that are knocking out the power that they do get restored," Theresa White, emergency management director for Fayette County, W.Va., told CNN. "That makes it really hard when you finally get one step forward and you end up three steps back."
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