Much of Georgia is enduring sweltering heat this week, with heat advisories across the southern part of the state and an extreme heat warning for parts of the coast. Heat index values between 95 and 105 degrees are expected across the state through this weekend, following brutal heat and humidity over the July 4 holiday last weekend.
The conditions go beyond an ordinary hot Georgia summer.
A northward shift in the jet stream last week created ultra-hot conditions known as a heat dome for much of the eastern U.S., blanketing the region in warm, moist air. That overlapped with another weather pattern to drive the heat up even more, according to Zachary Handlos, director of the atmospheric and oceanic sciences program at Georgia Tech.
The increased heat can be dangerous, he said.
“We’re already used to the hot and humid conditions, but it is amazingly even hotter and more humid than we’re used to,” Handlos said. “We’re already close to our breaking point as humans. Now you’re going beyond that breaking point into dangerous territory for long outdoor exposure.”
Critically, the heat and humidity have lingered even after the sun goes down. Nighttime cooling provides essential relief from extreme heat, allowing the body to recover.
“There have been major cities including Atlanta that just haven’t really cooled off at night,” Handlos said of the last week of brutal heat. “That can actually make the heat impacts actually worse because there’s never that time to cool off at night.”
Climate change is already driving up summer temperatures overall. Atlanta’s average summer temperature has increased by more than three degrees since 1970, according to Climate Central. Summer nights have warmed even more, with the average temperature climbing by four degrees. And climate change has added nearly a dozen more days per year with dangerous humid heat during the 2020s.
Beyond those impacts, Handlos said, climate change may be making heat domes like last week’s more common.
Models show the jet stream shifting farther north in the coming decades, which would bring warm air northward as well. There is also some evidence that a weakening jet stream could take on a more meandering, “increasingly wavy type of pattern,” Handlos said. There’s still some debate in the scientific community over that prediction, but it would lead to more of the conditions that create heat domes.
“The expectation is with a warming global average temperature that the probability, the frequency of occurrence of such heat dome type of setups certainly increases,” he said.
The weather cycle known as El Niño is also expected to bring warmer conditions this year, though Handlos said those effects will likely be more pronounced in the winter months.
