With Thursday’s seasonal solstice taking place amid a weeklong heatwave expected for the East Coast and Midwest, the summer of 2024 is coming in hot.

Extreme heat was forecast for Chicago, St. Louis, Indianapolis, Detroit, Cleveland, Cincinnati, Pittsburgh, Philadelphia, Boston, New York City and Albany, New York.

Models show the heat could last through Friday and beyond.

“The duration of this heat wave is notable and potentially the longest experienced in decades for some locations,” the federal Weather Prediction Center said.

A high pressure system called an upper-level ridge that is over the Ohio Valley is expanding over the Midwest and East Coast and will produce clear skies, warm, stable air and record-breaking temperatures in the 90s and beyond, forecasters say.

Some areas will experience temperatures as high as 105, according to the weather service. Forecasters say temperatures will reach as high as 25 degrees above normal for many areas under the summer system.

New temperature records could be set from the Ohio Valley and the Lower Great Lakes into the northern Mid-Atlantic and Northeast, the weather service said.

The National Weather Service office for Pittsburgh said it “could be the most impactful heat wave of the 21st century.”

Buffalo Public Schools said in a statement it was implementing half days for four of the week’s five days. The schedule will allow pre-K through 8th grade students go home by the end of the lunch hour.

Nights are likely to provide a minor dousing of relief, with low temperatures across that quarter of the nation to dip into the upper 60s and the 70s, they said.

Early Monday, the National Weather Service had 71 million Americans under a heat advisory or excessive heat watch as separate sections of the nation also expected to sweat.

On the northwest side of the heat, flash flooding could take place in the Dakotas and Minnesota on Monday, forecasters said. On the southwest side, rain pushing in from the Gulf of Mexico was expected in parts of Texas and Louisiana, possibly through Wednesday, they said.

The weather service is also on the lookout for any possible tropical storms developing in the Gulf, it said.

This article was originally published on NBCNews.com