OKLAHOMA CITY – As temperatures climbed into the 90s Sunday in Steele, N.D., a small window air conditioner in Paul and Betty Smokov’s ranch home just couldn’t keep up.

“It’s 82 in the house,” Betty Smokov said. “The heat is really oppressive and sticky.”

That observation could be made anywhere in the central United States. Heat advisories and warnings were in place in 17 states, from Texas to Michigan, as temperatures and humidity combined to make being outside uncomfortable for millions.

One National Weather Service forecaster called the heat wave “unrelenting” and said residents shouldn’t expect any relief soon: A so-called “heat dome” over the region isn’t moving much.

“The trend is not our friend right now,” said Daryl Williams, a forecaster in Norman.

In Oklahoma City, forecasters expected another day of 100-degree heat Sunday, which would be the 27th day this year the city has reached 100 or above. The city is on pace to break its record for such days — 50 set in 1980 — with triple-digit heat possible through September.

It’s even worse in western Oklahoma, where temperatures at 110 or above have been common in recent weeks.

In Chicago, city officials said a half-dozen cooling centers would remain open this week, as temperatures as high as 105 were forecast in Illinois.

Cooling centers also were open in Detroit to help residents who don’t have air conditioning at home. Others were heading toward water for relief, including 65-year-old Marcellus Washington, who walked through a park on the Detroit River that marks the border with Canada.

“A day like this, you can’t beat it,” Washington said. “It’s a heavenly day. It’s God’s weather.”

Others who had to be outside in the heat took precautions. North Dakota National Guard Capt. Dan Murphy said several hundred soldiers deployed for flood-fighting efforts in the Dakotas were required to take mandatory rest breaks in the shade.