It's been a hot summer with plenty of weather extremes — and it appears likely that the rest of August will bring more swelter.
The National Weather Service's Weather Prediction Center is forecasting dangerous heat over the Central U.S. this weekend, heat that is expected to rise to "well-above normal to record-breaking temperatures" in areas from the central Gulf Coast and lower Mississippi Valley to the northern High Plains. Next week, the heat is expected to extend into the Central Plains and Texas.
"We're looking at a prolonged period of excessive heat with the potential there for daily highs being broken this weekend all the way through next week," Zack Taylor, a meteorologist at the National Weather Service, tells NPR.
For some locations, particularly in the Midwest, this could be the hottest period of the summer so far, says Taylor. Those areas include portions of Iowa, Kansas, Nebraska and the Dakotas, where there's a potential to break several daily high records.
The latest from us and @NWSCPC regarding the dangerous heat wave which will expand across the Central and Southeast U.S. this weekend and next week. Numerous high temperature records will continue to fall through next week, with little overnight relief from the heat. pic.twitter.com/VwHpPVX1jT
— NWS Weather Prediction Center (@NWSWPC) August 18, 2023
What's the cause of this long stretch of very hot days? An upper-level ridge – a high-pressure area in the upper air – is going to be centered and persistent above the central U.S. It will be kept in place by a low-pressure area in the Western U.S., and interactions with Hurricane Hilary, which has prompted the first-ever tropical storm watch in Southern California.
"That's what's going to allow for this heat to build and intensify through next week and bring those dangerous heat conditions," says Taylor.
This situation is known as a heat dome. That's when a persistent region of high pressure traps heat over a particular area, for days or weeks at a time.
Climate change is making heat waves more intense and more frequent
This summer has already been awfully hot in the southern plains and the Gulf Coast. Now, even more of the U.S. that will feel the heat. In the coming days, a large portion of the country will see dangerous temperatures. Many areas could see heat indexes as high as 110 for several hours and potentially over several days next week.
The warming climate is making heat waves more frequent and intense. Last month, an international team of researchers said that the recent heat waves that have scorched U.S. cities would be "virtually impossible" without the influence of human-caused climate change.
And heat waves tend to compound.
"They are getting hotter," Kai Kornhuber, adjunct scientist at Columbia University and scientist at Climate Analytics, a climate think tank, told NPR's Lauren Sommer earlier this summer. "They are occurring at a higher frequency, so that also increases the likelihood of sequential heat waves."
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