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As much of the Eastern U.S. experiences potentially record-breaking daytime temperatures, the nights are also staying unusually warm, leaving the human body no time to recover. (Image credit: Kevin Dietsch)

As much of the Eastern U.S. experiences potentially record-breaking daytime temperatures, the nights are also staying unusually warm, leaving the human body no time to recover.

(Image credit: Kevin Dietsch)

The sun begins to rise over the Lincoln Memorial Reflecting Pool on Thursday in Washington, D.C. Temperatures in the nation's capital are expected to top 100 degrees as a heat wave stretching from the Midwest to the East Coast impacts up to 90 million Americans. Kevin Dietsch/Getty Images hide caption

Much of the U.S. is in the midst of dangerous and potentially record-breaking daytime temperatures as a heat dome has settled over the Midwest and the Atlantic Coast. But nighttime temperatures are staying unusually warm, too, raising the risk of heat exhaustion and heat stroke even higher, especially for people without access to air conditioning.

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"We're seeing temperatures well into the evening that are staying shockingly high and, in some cases, never dropping below 80 or 75 degrees. And this is really concerning," according to Ashley Ward, director of the Heat Policy Innovation Hub at Duke University's Nicholas Institute. Ward says that climate change is making the trend worse.

"We're not getting the opportunity for recovery overnight, as we've historically seen," she says. "Our bodies need it, of course, but plants and animals … also our energy infrastructure. We need to be able to cool off overnight."

In the Baltimore-D.C. region and southeastern Pennsylvania, including Philadelphia, highs on Thursday were expected to be in the low to mid 100s with heat indices around 110F, according to the National Weather Service forecast. Overnight lows are expected to remain in the low 80s for many of those areas.