NEW YORK — 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 in the grip of 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 heat exhaustion after wandering away from his northern Kentucky home Tuesday in temperatures that rose to 93 degrees.

In New Jersey, officials urged residents to check on their elderly or disabled neighbors during the heat wave.

Forecasters say temperatures in the 90s will combine with humidity to make it feel like 105 degrees in parts of the state Thursday.

Experts say the heat poses the biggest threat to the very young, the very old and pets.

The National Weather Service expects the heat wave there to break in the form of showers and thunderstorms on Saturday.

Utilities are monitoring usage as people rely on air conditioners to stay cool.

Cities, like Hoboken, have set up sprinklers in parks. Others are keeping swimming pools open later.

Amtrak said the heat loosened overhead power lines on the Northeast Corridor and that caused train delays on Wednesday afternoon.

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.

In Utah, a state biologist said heat and low water levels are to blame for a fish kill at Strawberry Reservoir.

Division of Wildlife Resources biologist Alan Ward told KSL-TV that about 600 fish have been found dead in the Ladders area of the lake about 55 miles southeast of Salt Lake City.

Ward says low water levels are killing aquatic vegetation, and high temperatures are lowering water oxygen levels.

He says temperatures in the 90s and 100s have a pronounced effect.

Drought has lowered water levels to a point that Ward says he hasn’t seen in his 13 years at Strawberry Reservoir.

The lake was full in 2011. It’s currently at about 79 percent.

The National Weather Service said it will feel like 105 degrees across parts of Illinois on Thursday.

The forecast calls for highs in the low-to-mid 90s with high humidity and sunshine, which will make it feel like it’s between 100 and 105 degrees. Friday should be even worse. That’s when the heat index climbs to 108 degrees.

Federal weather officials say the steamy weather could cause rolling blackouts and buckled pavement in that state.

Meanwhile, Illinois public health officials are opening cooling centers and warning people to drink plenty of fluids, check on neighbors and take precautions if they’re outside.

A heat advisory will remain in effect for Illinois through Friday evening before cooler weather arrives for the weekend.

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.