A sprawling blanket of sizzling and humid air smothering the nation’s midsection this week has challenged temperature information, compelled colleges to cancel courses and left residents sweating from the Northwoods to the Gulf Coast.

Even in a season crammed with different local weather shocks, this blast of late-summer warmth within the central United States stands out for its breadth and its mixture of excessive temperatures and suffocating humidity — in areas together with some which can be extra related to frigid winters than insufferable summers.

Across a whole lot of miles, from Mississippi to Missouri to Minnesota, cooling facilities have opened, colleges with out air-conditioning have dismissed early or closed outright, and residents have tried to restrict time outdoor.

In Omaha, a 1-year-old woman died on Monday after she had been left in a day care heart’s van, in accordance with the native police. Temperatures within the space had reached 98 levels that afternoon. The driver of the van was arrested on Monday on fees of kid abuse by neglect leading to loss of life.

“I’ve never seen humidity like this,” mentioned Eric L. Harris, who lives in Lincoln, Neb., the place temperatures surpassed 100 levels on Tuesday and had been anticipated to take action once more on Wednesday and Thursday.

Mr. Harris, who has been amassing signatures for a proposed poll query on paid sick go away, mentioned the climate made that work particularly troublesome.

“My biggest fear isn’t trying to get people with opposing views to listen to me,” he mentioned. “It’s that without measures to protect me, I would likely get heat stroke just from standing out in this heat.”

Across the continent, this summer season has already been outlined by climate extremes: lethal wildfires in Hawaii, blankets of smoke from Canadian wildfires, floods brought on by a uncommon tropical storm in California, weeks of stifling warmth in Arizona. Though linking particular person occasions to local weather change typically takes time, researchers have warned that harmful climate occasions will turn into extra widespread because the planet warms.

For many Midwestern states, the excessive temperatures this week have introduced added distress in a summer season already made troublesome by drought. In a merciless meteorological flip, that drought has exacerbated the warmth.

“The ground is already really dry — it doesn’t take much for the heat to kind of just build up over there,” mentioned Paul Pastelok, a senior meteorologist at AccuWeather. “And that’s what makes it a bigger heat dome that we’re seeing right now.”

In the Minneapolis space, higher identified for its foreboding winter situations, forecasters mentioned every day temperature information might fall on each Tuesday and Wednesday, with readings of 99 or 100 levels doable.

Tyler Hasenstein, a National Weather Service meteorologist in Minnesota, mentioned a warmth dome of this scale may settle over the state each 5 years or so, “but those typically happen in June, July — and not August, which is kind of the weird thing in this case.” The temperatures had been additionally not anticipated to drop a lot after sundown, he mentioned.

Meteorologists mentioned excessive temperatures had been forecast to achieve as much as 20 levels above common all through Iowa and neighboring states over the following few days. The humidity will make it really feel much more oppressive, with warmth indexes that might method 120 levels. Forecasters have issued warmth alerts, starting from advisories to extreme warmth warnings, for roughly 100 million individuals throughout 22 states.

In Adel, Iowa, the place it was cloudless and within the 90s by noon on Tuesday, the excessive temperatures meant Amy Heinz was not in a position to let the canine play exterior on the animal rescue heart she runs.

“Some of them are going crazy in their kennels,” Ms. Heinz mentioned, however the different was merely not secure.

Even in a spot like Iowa, immune from hurricanes and coastal disasters, Ms. Heinz mentioned excessive situations had been a rising concern.

“Every year the weather seems to get worse and worse,” she mentioned. “Between the flooding and the heat, and then we have the extreme cold that we deal with in the winter, it seems it’s worse than it used to be.”

With extra of the nation anticipated to undergo from excessive warmth within the days forward, contingency plans had been already being put in place.

Kevin Russell, the superintendent of Downers Grove Grade School District 58 in suburban Chicago, mentioned he began maintaining a tally of the forecast late final week. Most buildings in his district are usually not totally air-conditioned, that means the 100-degree temperatures that forecasters have mentioned are untenable.

“We do have limited air-conditioned spaces, so what we’ll do on those hotter days — in the high 80s or even the low 90s — we will rotate students and staff through cooling stations,” Dr. Russell mentioned. “However, when you start talking about 100-plus, you really need to be in that cooling station all the time.”

The first day of sophistication in Downers Grove had been set for Wednesday, however Dr. Russell made the troublesome option to push that again to Friday, when cooler climate is anticipated.

“We have thousands of kids in Downers Grove with their backpacks all ready to go and super excited to start the school year,” Dr. Russell mentioned. “Having to delay that, no one takes any joy in that.”

But there may be good news forward. Plans are in place to put in air-conditioning at all the district’s colleges.

Judson Jones and Lauren McCarthy contributed reporting.