Heat wave spreads across US. When will it end?

Cooler temperatures are within sight but likely not soon enough and cool enough for a large swath of the country hit with dangerously high temperatures for days as the largest heat wave of the summer failed to budge from South Dakota to Massachusetts.

The relief is expected to begin arriving Thursday in some regions of the country as a cold front drops south from Canada. But it is not soon enough for others. New York City, for instance, is bracing for another day of temperatures in the high 90s.

Cooler temperatures are likely to sweep through the Midwest and into the Mid-Atlantic and Northeast regions by Saturday. They might be accompanied by severe thunderstorms.

The largest heat wave of the summer has stagnated over large regions, bringing sizzling temperatures and little hope of relief without rain, a growing possibility for some hard-hit areas as the weekend approaches.

Most states in the U.S. had at least one region where the temperature hit 90 degrees Wednesday, according to the National Weather Service, though the worst heat was in the Midwest to Northeast. Humid air just made it all feel worse, with heat indexes in some places over 100.

It was hot enough to buckle highway pavement in several states. Firefighters in Indianapolis evacuated 300 people from a senior living community after a power outage knocked out the air conditioning. The state of Illinois opened cooling centers. The Environmental Protection Agency said the heat was contributing to air pollution in New England.

Officials are blaming hot weather for at least one death. A 78-year-old Alzheimer's patient died of heatexhaustion after wandering away from his northern Kentucky home Tuesday in temperatures that rose to 93 degrees.

In New York City, where it was 96 degrees, sidewalk food vendor Ahmad Qayumi said that by 11 a.m., the cramped space inside his steel-walled cart got so hot that he had to turn off his grill and coffee machine.

"It was just too hot. I couldn't breathe," he said, turning away a customer who asked for a hamburger. "Just cold drinks," he said.

Amid the heat, officials in Washington D.C.'s Maryland suburbs worked to keep a failing water main from cutting off hundreds of thousands of people, just when they needed it most. People in Prince George's County were asked not to run their faucets, water their lawns or flush toilets to keep the water system from emptying during emergency repairs.

Firefighters in southern California faced brutally hot — but dangerously dry — conditions as they battled a wildfire outside Palm Springs that had already consumed seven homes.

New Mexico and parts of Texas turned out to be rare outposts of cool air Wednesday — but not without trouble of their own: heavy rains prompted flood watches and warnings in some areas. More than five inches of rain fell in 24 hours in Plainview, north of Lubbock, according to the National Weather Service.

At the World Trade Center reconstruction site in New York City, workers building a rail hub dripped under their hardhats, thick gloves and heavy-duty boots. Some wore towels around their necks to wipe away the sweat.

"We're drinking a lot of water, down under by the tracks, in and out of the sun all day — very hot," said carpenter Elizabeth Fontanez, of the Bronx, who labored with 20 pounds of tools and safety equipment strapped to her waist. Since the heat wave began, she said she has been changing shirts several times during her shifts.

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Associated Press writer Verena Dobnik contributed to this report.