The heat is on: When will conditions let up?

(NEXSTAR) — For much of the country right now, there’s no sugarcoating it: it’s hot. Outside, it may feel like you’re standing in an air fryer or in front of a heat vent set to “scorching.”

Even the National Weather Service was blunt: Conditions on Tuesday were “dangerous” as the heat index exceeded 100 degrees Fahrenheit in some areas. It warned about a risk of heat-related illnesses, especially among people without air conditioning.

Unfortunately, it may not be letting up soon, either.

Two heat domes were expected to unite over the U.S. this week, bringing some regions the hottest temperatures they’ve seen this year. These weather systems can trap heat and humidity in an area for days.

Across central and eastern states, the heat index, or what the mix of humidity and air temperature feels like to you, could climb to between 105 and 115 degrees, according to Jim Danner, a senior meteorologist with Nexstar.

Heat advisories and warnings on Tuesday stretch from the central Gulf states north into the Plains, Midwest, Ohio Valley, and New England, a map from the National Weather Service shows.

The heat is expected to linger through the week, Cody Nickel, a meteorologist at Nexstar’s WRBL, said.

In the coming days, the heat wave is expected to expand into the western U.S., though those in the Northeast and other parts of the country will still be hot, forecasters say.

The heat wave will also likely coincide with the Fourth of July holiday weekend, providing additional risk as more people have cookouts or watch fireworks outside for the 250th anniversary of American independence.

Most will see the heat carry into next week, the NWS shows.

The U.S., excluding Alaska, has an above-average chance of seeing hotter-than-normal temperatures into mid-July, according to the NWS’s Climate Prediction Center temperature outlook.

If you’re going to be in the heat this week, experts recommend taking the necessary precautions.

People can be caught off guard by the first heat wave of the year, said Dr. Roy Elrod, chief of staff at DMC Detroit Receiving Hospital.

“You’re happy winter’s gone, you’re ready to enjoy the summer, you’ve just been aching for it,” Elrod said. “And so, I think we slip into kind of a position where we think it’s got to be OK.”

Heat-related injuries can happen in a matter of minutes, he said, especially to those who don’t prepare for the weather by hydrating, wearing light clothing, avoiding the hottest times of the day and minimizing exposure to the sun.

The Associated Press contributed to this report.