A dramatic cooldown is on the way for the US. But it comes with a cost

CNN

6 days ago

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It's been an abnormally hot summer in much of the eastern half of the United States with multiple punishing heat domes, sweltering nights and plenty of humidity to go around, but some relief is finally on the horizon.
A major weather pattern change beginning later this week will bring high temperatures more like early June — nearly 20 degrees cooler than they are now — to millions currently reeling through some of summer's most intense heat.
The upcoming cooldown is tied to an expansive area of high pressure expected to track south out of Canada later this week, and a lengthy cold front racing down ahead of it. The north-central US will be the first beneficiary of cooler conditions on Wednesday and more of the eastern half of the US will follow in the coming days, with some of the coolest temperatures coming just in time for the weekend.
But a dramatic cooldown like this always comes at a cost, and in this case it's rain and thunderstorms with a renewed risk of flash flooding for areas that have already been hit hard during a summer full of it.
Here's when the heat will finally break and where flooding could become an issue later this week.
More than 150 million people from the central US to the East Coast are under a Level 3 of 4 or Level 4 of 4 heat risk Tuesday, according to the National Weather Service, as high temperatures climb into the 90s and the heat index soars even higher.
It's another brutal day of heat for the dozens of cities and towns from the East Coast to the Mississippi Valley that are having one of their 10-hottest summers to date as of July 27, according to data from NOAA's National Climatic Data Center.
Stretches of extreme heat are getting more intense and lasting longer as the world warms due to fossil fuel pollution and colder spells like the upcoming one are becoming less common.
It isn't unheard of to have a handful of cooler days in the latter part of summer, but the upcoming change will feel especially jarring given how hot previous weeks have been.
Temperatures will ease dramatically on Wednesday from the north-central US to parts of the Northeast. Chicago, for example, soared into the 90s Tuesday but will struggle to even reach 80 degrees on Wednesday.
The cooling trend will continue Thursday with widespread temperatures in the 70s in much of the Plains, Midwest, Northeast and parts of the Ohio Valley. St Louis reached well into the 90s Tuesday and temperatures in the low 90s are expected Wednesday, but the city might not even hit 80 degrees Thursday.
Temperatures will ease in the South too, though not nearly as drastically as farther north. Little Rock, Arkansas, could rise to nearly 100 degrees on Tuesday and Wednesday, but reach the mid-90s by Thursday.
Friday, the first day of August, could be the coolest day of the week for parts of the Midwest, Ohio Valley and Northeast. New York City's high temperature on Friday will only reach the low 70s after being in the upper 90s Tuesday and mid-90s Wednesday. That's similar to what the city records in the first days of June.
After high temperatures near 97 degrees on Tuesday and Wednesday, Washington, DC, could have a high in the upper 70s on Friday, which happens on only a few days each August. High temperatures are typically in the 80s in August in the nation's capital.
Cooler conditions will finally reach more of the South over the weekend. Atlanta hasn't had a high temperature less than 80 degrees since May, but that streak could finally be broken on Sunday. Areas farther north will be quite pleasant over the weekend as high pressure remains in place.
The cooler conditions will not last forever. The latest forecasts from the Climate Prediction Center indicate above-normal temperatures are likely to return during the first full week of August.
Stormy weather could stretch over a large portion of the central and eastern US on Wednesday as humid air pours north out of the Gulf and the cold front starts to slice south.
Storms spark to life when cooler, drier air and very warm and humid air clash, like what's expected this week. Wet weather will also be drawn out over multiple days given the slow trek south of the cold front.
Parts of the Midwest are under a Level 2 of 4 risk of flooding rainfall on Wednesday with a massive Level 1 of 4 area stretching from the Gulf Coast to the Northeast, according to the Weather Prediction Center.
The real concern begins Thursday for areas that have dealt with disruptive and deadly flooding this summer. A Level 2 of 4 risk of flooding rainfall is in place for parts of the Northeast and mid-Atlantic, including New York City, Philadelphia and Washington, DC.
Nearly all of New Jersey is in the risk area. The state has been slammed by flooding this summer, including when at least two people were killed two weeks ago. The increased risk also includes parts of Virginia that have flooded multiple times this season.
The flood risk shifts south into the Carolinas and part of Georgia on Friday, more states all too familiar with serious flooding this summer. Tropical Storm Chantal's flooding rainfall killed at least one person in North Carolina in early July.