LOUISVILLE, Ky. — A late summer heatwave is set to return and bring unseasonably hot temperatures and dry weather to the central third of the country – including Kentuckiana. This may rival the heatwave seen in the final week of July.
Mid-August is starting with temperatures much cooler than normal across the Ohio Valley thanks to an upper-level trough. You could perhaps call it a “false autumn.”
This trough brought us rain Monday and has also brought a chunk of cooler, drier Canadian air with it. That’s why temperatures in the next couple of days will be so comfortable with low humidity.
Unfortunately for autumn lovers, it isn’t going to last.
A large dome of high pressure will be building over the western half of the country during the second part of this week. As it does, a second smaller (but weaker) trough will swing by just to our north Thursday.
That may bring a few isolated showers to the region overnight Thursday thanks to a weak cold front helping to reinforce milder air, but confidence in the rain is low.
By Saturday we’ll notice the warmer temperatures as we climb back into the middle and upper 80s for afternoon high temperatures with increasing humidity.
Sunday sees us back into the low 90s, with early next week high temperatures reaching the middle, possibly upper 90s in urban areas like Louisville, within the realm of possibility.
The Climate Prediction Center has placed the eastern two-thirds of the continental U.S. under high certainty of warmer than normal temperatures from Aug. 20 through Aug. 25 with a high likelihood of drier than normal conditions.
The 8-14 day outlook (from Aug. 22 through Aug. 28) is similar but to a lesser extent due to normal long-term forecasting uncertainty and possible changes in the weather pattern.
Although Kentuckiana has largely avoided the extreme heatwaves Texas, Oklahoma, Arizona, and others have faced this summer, we are still technically in the hottest time of the year for our region.
For Louisville specifically, our average high temperature is 89° through Aug. 19. Afterward, we start to slowly cool off as we head toward summer.
As you can see from our forecast, that doesn’t mean we can’t still have very hot days. Temperatures have soared well into the 90s as late as October in Louisville (see 2019), so we still have a ways to go before the heat truly backs off for the year.
Don’t expect much rain during the wave of heat either. Hopefully, you saw some meaningful rainfall over the last few days because it’s likely the last rain we’ll see for some time.
A large portion of the country is expected to stay dry over the next week, as of Tuesday, Aug. 15.
This may result in drought conditions developing again if we stay dry through the next 10-14 days. Some models show no appreciable rainfall (so basically zero) through at least Aug. 25.
How long this late summer heatwave lasts is still a bit uncertain as weather models begin to diverge in their assessment after next Tuesday.
Confidence is medium-to-high in hot weather from Sunday, Aug. 20 through Wednesday, Aug. 23.
The biggest questions: how hot do we get, how long does it last, and when will rain return?
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Meteorologist Alden German
Facebook: Facebook.com/AldenGermanWX | Twitter: @WXAlden