Sweating crowds on the East Coast and in the Midwest flocked to waterfronts and urban cooling centers Thursday to escape a massive heat wave that could intensify on Friday.
The National Weather Service issued excessive heat warnings for wide swaths of the country's mid-section and East Coast, saying the combined heat and humidity could spike the heat index or "real feel" of the warmth to 115 degrees through Saturday.
Longstanding records in Philadelphia and other cities may melt away on Friday, according to meteorologist Meghan Evans of AccuWeather.com.
In Cleveland, Ohio, customers flocked to the Dairy Queen on Detroit Avenue to get out from the heat — 96 degrees, making it the hottest day in 16 years.
"We've had hundreds and hundreds of people coming in from off the street," said Stasia Williams, a Dairy Queen manager. "It's so hot outside that people come in and just ask for a sip of water."
By early Thursday afternoon in New York City, the thermometer hit 91, but it felt more like 112, according to Accuweather.com. By late Thursday morning, the heat index at Philadelphia International Airport had reached 100.2, more oppressive than conditions in Miami, where the index was 98, philly.com reported.
Other cities watching their local heat indexes rise into the triple digits because of the oppressive mix of high temperatures and humidity included Tulsa, St. Louis, Buffalo, and Washington, D.C., according to the weather service.
By the weekend the heat was expected to cover nearly 50 percent of the country and impact nearly half the population, according to AccuWeather.com forecaster Mary Yoon.
"What makes this heat wave so impressive is the pure size and longevity," said Yoon.
"Through the rest of this week and into the weekend at least 15 states starting from the Southern Plains and Midwest and much of the Northeast will witness 90 degree plus temperatures with high humidity," she said.
Cooling centers in Richmond, Virginia, and New York City welcomed overheated residents and a truck labeled "Water Fountain on the Go" cruised Manhattan streets, offering to refill empty water bottles to keep residents hydrated.
Kevin Roth, the lead meteorologist at the Weather Channel, said Thursday that the "dangerously high temperatures and humidity levels" would continue from Kansas to the Lower Great Lakes, with temps soaring as high as 120 degrees.
But a cold front would temporarily bring a measure of relief to the northern Plains, Upper Midwest and northern Great Lakes, Roth said.
In the central United States, where the high temperatures have killed nearly two dozen already, more deaths were tied to the heat.
"Do not take this threat lightly," the NWS warned in a statement on its website, noting the extreme temperatures are particularly dangerous for the elderly and the very young.
"The length of this heat wave will pose a very real and dangerous health risk to these at-risk groups and those that do not have access to air conditioning."
"This heat wave is widespread," Susan Buchanan, spokeswoman with the National Weather Service, told msnbc.com on Thursday evening. "It has persisted for a long time. It has added a lot of humidity. It's more dangerous for the human body."
A look at the nation:
New York, New Jersey
Con Edison expected scattered outages in coming days amid an anticipated all-time high in electrical demand in New York, said utility spokesman John Micksid.
New Yorkers can expect temps above 100 degrees on Friday, possibly breaking more records, and the intense heat will sizzle through the weekend, with perhaps a bit of relief on Sunday, WNBC reported.
"This is Day 1 of a three-day battle for us," Micksid said.
The MTA reported Thursday that the heat was causing malfunctions on the platform countdown clocks at about 13 stations. This is caused by equipment rooms heating to temperatures of 120 degrees and higher. In those cases, the equipment has to be shut off so it won't be damaged.
Nearly all of New Jersey is under an excessive heat warning through Saturday evening as a large dome of high pressure brings stifling heat and humidity to the region.
Illinois
Chicago endured a fifth consecutive day of abnormally high temperatures with the heat index hitting 110 in the early afternoon.
Two people died from the heat in an Illinois county near the Mississippi River on Wednesday, St. Clair County Coroner Rick Stone said on Thursday.
They were identified as Willie Gill, 72, of East St. Louis, Illinois, whose body was found dead of heat stroke in a ditch near his home; and Kevin Miller, 51, of Belleville, Illinois, who was found dead of a heat-related heart attack on his front porch, which faced westward toward the setting sun.
Unhealthy smog levels triggered by the heat were reported in Chicago, where residents were asked by the Illinois Environmental Protection Agency to reduce polluting activities such as idling cars and mowing lawns.
Oklahoma
The heat has exacerbated a severe drought. Gov. Mary Fallin said she planned to ease commercial vehicle restrictions to speed delivery of hay and other feed to cattle whose grazing areas have been destroyed by the weather.
Fallin said she would amend an existing drought-related emergency declaration she issued earlier this year to allow hay-haulers to operate bigger trucks with heavier loads on the state's roads.
"We have cattle that are starving," Fallin told Reuters, "and we have certain areas of the state where we need to get the hay delivered to the farmers and the ranchers and the cattlemen."
Missouri and Kansas
An elderly woman whose body was found in her bedroom in St. Louis, where a working air conditioner had not been turned on despite 99-degree temperatures, was determined on Wednesday to have died of heat stroke.
Similar causes of death were reported Thursday in Kansas City, where a woman in her early 80s died, and in Hutchinson, Kansas, where three elderly people were found dead in their separate homes on Wednesday.
Of those who died in Hutchinson, one had a ceiling fan and another, a 76-year-old man, an air conditioner.
"He had an air-conditioning unit in the window but didn't use it because he didn't want to pay the electric bill," said Hutchinson Police Sergeant Thad Pickard.
Temperatures in the area, which is about 15 miles east of St. Louis, reached 100 degrees on Wednesday and again on Thursday.