Heat dome will scorch the US into Fourth of July. Why so hot?

Get ready for some record high temperatures.

A heat dome will impact millions of Americans over the next couple of days and temperatures will reach triple digits in some regions as the Fourth of July holiday approaches. New York City will hit 95 on the July 4, according to AccuWeather Senior Meteorologist Alan Reppert.

"That would make it the hottest 4th of July since 2010, when Central Park reached 96°F," Reppert said.

But what exactly is a heat dome? USA TODAY asked Reppert to explain.

What's causing the dangerous temperatures? Heat domes

A heat dome acts like a lid on the atmosphere, trapping heat over the same region for an extended period. "Heat Domes are caused by a strong high pressure that extends over a large area and feeds on the heat and even expands a bit," Reppert said, adding that they can last for some time as they typically move slower than other weather patterns.

"The jet stream lifts north due to storms being slow to move over the West Coast and east of the system warm air surges northward bringing heat over much of the central and eastern part of the nation. There is also a storm over the Atlantic that is not as strong as the storm in the west, but it locks in this ridge in," Reppert said.

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According to AccuWeather, heat domes can also prevent clouds from forming, increasing sunshine that boosts temperatures. The uninterrupted sun dries out soil increasing drought risk, and light winds allow pollutants to build up, worsening air quality, particularly in urban areas.

How the heat dome is expected to unfold this week

"For many Americans, the heat is already here. However, in many cities and communities, the hottest days are still ahead. As temperatures and AccuWeather RealFeel Temperatures continue to climb through the week, it's important to take the heat seriously by limiting time outdoors during the hottest part of the day, staying hydrated and checking on those most at risk for heat-related illness, including the elderly, children and pets," said AccuWeather expert meteorologist Carl Erickson.

Here's how hot it could get leading into the 4th of July

How humidity, heat can be a dangerous combination

It's not just the heat, it's the humidity too.

The National Weather Service warns that "extreme heat and humidity will significantly increase the potential for heat-related illnesses, particularly for those working or participating in outdoor activities."

"The intensity and length of the extreme heat will exacerbate impacts to both people and infrastructure. This is not the kind of heat event we see every year and could be the hottest period of weather the area has experienced since July 2011. The heat will be especially dangerous to the young, the elderly, and other vulnerable populations," according to the NWS recent release.

This chart shows how hot it feels when the effects of humidity and high temperatures are combined, a measurement known as the heat index:

Know the signs of heat stroke, heat exhaustion

Hot, humid conditions make it difficult for the body to regulate its temperature. Your health can depend on recognizing the warning signs of too much heat and knowing how to act.

According to the Centers for Disease Control and Prevention, the following are common signs and symptoms of heat-related illness:

Additional tips to stay cool

• Drink water, more than usual, no matter how active you are. Don't wait until you're thirsty. Make sure your pets have plenty to drink.
• Avoid sugar, alcohol or caffeine: Liquids with large amounts of these substances can increase loss of body fluid.
• Stay in air-conditioned buildings as much as possible.
• Take cool showers or baths.
• Limit outdoor activity, especially in the middle of the day.
• Use drapes or shades on windows to keep out the sun.
• Limit oven and stove use to keep in-home temperatures lower.
• Wear light-colored, loose-fitting clothing to improve perspiration evaporation.

SOURCE AccuWeather, National Weather Service, Centers for Disease Control and Prevention and USA TODAY research

This article originally appeared on USA TODAY: Heat dome will scorch the US into Fourth of July. Why so hot?

Reporting by Janet Loehrke, USA TODAY / USA TODAY

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Copyright Reuters or USA Today Network via Reuters Connect

This story was originally published July 1, 2026 at 12:01 AM.