However, daytime temperatures of over 35 degrees Celsius and heat indices of over 38 degrees Celsius will not be the only heat threat in the coming week.

Nighttime temperatures won’t see much improvement. The National Weather Service predicts that temperatures will be above 70 degrees Fahrenheit every night between now and Thursday, the threshold at which scientists call a warm night. This weekend, nighttime temperatures will be above 75 degrees Fahrenheit both times, the threshold at which climate scientists call a very warm night.

“Unless temperatures drop very low at night, nothing has a chance to cool down,” said Mark Lockhart, director of the Durham County Office of Emergency Services.

This effect is felt more in urban areas, where asphalt and concrete absorb heat during the day and remain warm even after sunset, Lockhart added. According to the U.S. Environmental Protection Agency, temperatures in urban areas are typically about 2 to 5 degrees warmer than in rural areas because of this effect.

Kathie Dello, North Carolina state climatologist and director of the North Carolina State Office of Climate, said the higher nighttime temperatures increase the risk for people who do not have access to air conditioning, especially children, the elderly and pregnant women.

“Heat is simply a stressor for many underlying conditions. And that’s why it’s sometimes so hard to quantify heat-related illness and death, because you might come into the emergency room with cardiac arrest or dehydration and the heat may have made the situation worse or it might not have happened without the heat exposure,” Dello said.

Climate change and nighttime low temperatures

According to data from the NC State Climate Office, this weekend’s low temperatures will be about 8 to 9 degrees above the average minimum temperature at Raleigh-Durham International Airport between 1991 and 2020.

The NC Climate Science Report, released in 2020, found that nighttime temperatures are a key indicator of climate change in the state. While the number of days above 90 or 95 degrees has not increased since 1900, scientists found that the number of nights when temperatures remained above 70 or 75 degrees has increased.

Scientists also found that the number of very warm nights is likely to increase by 2040, particularly in the Piedmont and Coastal Plain regions.

In the 1940s to 1960s, Dello said, nights with temperatures above 24 degrees were extremely rare, occurring about once per decade. According to the current forecast, Raleigh would reach that value twice this weekend.

“We are observing that night temperatures are rising significantly,” said Dello.

Scientists around the world see clouds as a key factor in the rise in nighttime temperatures. As the planet warms, the atmosphere can hold more moisture and more clouds form.

At night, these clouds cause temperatures to drop less than they would under clear skies. This is because the clouds release the heat they absorbed from sunlight during the day to the surface, while the heat coming from the surface keeps the underside of the clouds warm.

In places with thicker cloud cover, temperatures warmed faster at night than during the day, researchers from the United Kingdom found in a 2020 study.

How to stay cool overnight

People can protect themselves by consciously lowering their body temperature in the evening and working to keep it low, Dello says.

Measures such as soaking feet or arms in cold water, taking a cool shower, and sleeping in as cool a place as possible are helpful. Another consideration is to eat dinner earlier to avoid a rise in body temperature during digestion.

It can also be helpful to wipe your arms, neck and head with a towel dipped in cold water and then sit in front of a fan, Ashley Ward, director of Duke University’s Heat Policy Innovation Hub, told The News & Observer. This helps the body mimic the cooling effect of sweating.

“After a day outside or a hot day, it really helps a lot to come home and try to cool down as quickly as possible or take the extra step and take a cold shower,” Dello said.

This story was produced with financial support from the Hartfield Foundation and the Green South Foundation in partnership with Journalism Funding Partners as part of an independent journalism grants program. N&O retains full editorial control over the work. If you would like to support local journalism, you can take out a digital subscription. You can do so here.