JEFFREY BROWN: Some of the hottest weather on record kept dozens of states on a slow burn today. Temperatures topped out at 100 degrees and higher in city after city.
From parks and playgrounds to football fields and offices, nearly 200 million Americans spent this day under some form of warning about the scorching heat.
MAN: Let's go in. It's too hot out here.
MAN: Absolutely horrendous heat.
WOMAN: Oh, my goodness. At least my work is air-conditioned.
JEFFREY BROWN: The relentless, stifling combination of extreme heat and humidity formed a so-called heat dome over a vast region.
AccuWeather meteorologist Evan Myers:
EVAN MYERS, AccuWeather: Well, really, what we're talking about is just a massive area of high pressure that's been building heat out of the Southwestern part of the country, back where the drought is across portions of New Mexico and Texas, and that's just been expanding northward all the way up into Minnesota.
JEFFREY BROWN: The dome is partly the product of a fluctuation in Pacific Ocean temperatures, known as La Nina, that deflects the jet stream out of its normal path.
EVAN MYERS: That's one reason that's pulling up hot air out of Mexico, and also the drought that's been in effect now in the Western part of the country and the middle part of the country is also helping this heat expand.
JEFFREY BROWN: The effect has been so intense, in fact, that on Tuesday, superheated expanded metal and concrete caused eight water main breaks in Oklahoma City.
MAN: I turned around to get the shampoo, put it in my hand, getting ready to raise it up to my head, and the water goes off.
JEFFREY BROWN: Blistering weather also buckled highways in Iowa, where temperatures soared to 126 degrees this week.
In Minnesota, Interstate 94 in Minneapolis had to be closed for a time, after pavement on two of its lanes split open. Heat indexes in the Twin Cities reached as high as 115 degrees in recent days. And more than 50 people were treated for heat-related illness at Monday's Twins-Indians baseball game.
Long weeks of heat have also fueled the growth of dangerous algae in lakes and ponds, killing fish and threatening livestock. In Chicago, today's forecasted high was 97 degrees, the worst in six years.
WOMAN: You know, the heat's pretty miserable. I think the kids are doing better than I am, actually. But it's very hot.
MAN: Today will be hot. I'm already...
WOMAN: It's muggy. I'm sweating a lot already.
WOMAN: This 72-year-old is going in that water, honey.
JEFFREY BROWN: Residents have swarmed the city's 24 beaches in recent days, but as hot air blew over the cooler waters of Lake Michigan yesterday, it stirred up a soupy fog. Lifeguards had to turn away swimmers seeking relief because they could not see beyond the water's edge.
In city after city, cooling centers opened to shelter those without air conditioning of their own, even as utilities strained to keep up. As the heat dome expands east, triple digits are expected along the Atlantic Coast by Friday. It is, says meteorologist Myers, one for the record books.
EVAN MYERS: Temperatures have reached triple digits, 100 degrees or higher in 17 states Tuesday and Wednesday and 90 or above in 40 states. So, certainly, the extent, the geographical area that the heat wave is covering is fairly extraordinary. You don't usually get something quite this massive, maybe every 10, 15 years. In fact, we're looking at temperatures probably not this high since about 15 years ago.
JEFFREY BROWN: For some of the Plains states, relief could finally be on the way with cooler air from the jet stream expected to push the hot air out later this week.