BELZONI, Miss. (AP) — With another wave of dangerous cold heading for the U.S. South on Friday, experts say the risk of hypothermia heightens for people in parts of Mississippi and Tennessee who are entering their sixth day trapped at home without power in subfreezing temperatures.

“The longer you’re exposed to the cold, the worse it is,” said Dr. Hans House, a professor of emergency medicine at the University of Iowa. “The body can handle cold temperatures briefly very well, but the prolonged exposure is a problem.”

The National Weather Service said arctic air moving into the Southeast will cause already frigid temperatures to plummet into the teens (minus 10 degrees Celsius) on Friday night in cities like Nashville, where more than 79,000 homes and businesses still lacked power nearly a week after a massive storm dumped snow and ice across the eastern U.S.

People who are more vulnerable — the elderly, infants and those with underlying health conditions — may have started experiencing hypothermia symptoms within hours of being exposed to the frigid temperatures, explained Dr. Zheng Ben Ma, medical director of the University of Washington Medical Center’s northwest emergency department. That includes everything from exhaustion to slurred speech and memory loss.

But almost a week in and the situation is nearing a turning point, he explained: Younger people who are generally healthy could potentially begin to fall victim to these symptoms as well.

“Once you get into days six, seven, upwards of 10, then even a healthy, resilient person will be more predisposed to experiencing some of those deleterious effects of the cold temperature,” he said.

Hundreds of National Guard troops mobilized Thursday in Mississippi and Tennessee to clear debris and assist people stranded in cars or stuck at homes.

Mississippi Gov. Tate Reeves said Guard troops were delivering meals, blankets and other supplies by truck and helicopter. And in Tennessee, Gov. Bill Lee said crews had distributed more than 600 units of warming supplies and over 2,200 gallons (8,328 liters) of gas and diesel.

Nashville Mayor Freddie O’Connell said that they have the most line workers, crews and vegetation support workers in the city utility’s history as they work to get electricity back for everyone.

But the exact timeline for power to be restored, especially in more rural areas, remains unclear.

At least 85 people have died in areas affected by bitter cold from Texas to New Jersey. Roughly half the deaths were reported in Tennessee, Mississippi and Louisiana. While some deaths have been attributed to hypothermia, others are suspected to be related to carbon monoxide exposure.

Dr. Abhi Mehrotra, an emergency medicine physician with the University of North Carolina at Chapel Hill, said it’s important to make sure heat sources used indoors, including generators, are not emitting carbon monoxide, which could be deadly.

More than 230,000 homes and businesses were without electricity Thursday night, according to the outage tracking website poweroutage.us. The vast majority were in Mississippi and Tennessee, with roughly 87,000 each.

Mississippi officials say it’s the state’s worst winter storm since 1994. About 80 warming centers were opened across the state, known as one of the nation’s poorest.

Forecasters say the subfreezing weather will persist in the eastern U.S. into February and there’s high chance of heavy snow in the Carolinas, Virginia and northeast Georgia this weekend, possibly up to a foot (30 centimeters) in parts of North Carolina. Snow is also possible along the East Coast from Maryland to Maine.

The National Weather Service said there was a chance of freezing rain Thursday night in parts of Mississippi, and light snow showers could hit Nashville overnight Friday. Forecasters said the extreme cold and subzero wind chills (minus 18 C) represented the greatest danger.

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Bynum reported from Savannah, Georgia, and Thanawala from Atlanta. Associated Press writers Jeff Martin in Atlanta; Jonathan Mattise and Travis Loller in Nashville, Tennessee; Sarah Brumfield in Washington; Devi Shastri in Milwaukee and Hallie Golden in Seattle contributed.