On August 30, I wrote that a taste of fall was likely in store in about a week, with high temps dropping into the 60s and lows into the 40s for a few days.
Well, here we are, “in about a week,” and while the transition to fall is certainly underway, those 40s/60s temps are nowhere to be found.
The first part of the step-down into fall that I wrote about back on August 30 actually happened. A cold front pushed through the region on Friday, bringing absolutely magnificent weather to our region for the holiday weekend. If you were at the high school football games on Friday night, you likely noticed how the feel of the air changed as drier air came washing in. Before the game, it was very muggy. By the time the game ended, humidity levels had dropped significantly. And so while the weekend was still quite warm, the lower dew points made it feel much more like fall, and nighttime temperatures dropping into the 50s made it feel downright cool Saturday, Sunday and Monday mornings.
What is not happening is the second wave of cooler air that was initially expected for this week. So what happened to it? Look out west.
Denver has been experiencing a very hot start to September. But that’s about to come to an abrupt halt as a mega trough swings through the Rockies and delivers some much colder air. It’s going to be a wild weather swing for the Mile High City. Today they’re in the 90s. Tomorrow it’s going to start snowing. And more than a foot of snow could accumulate in some areas by daybreak Wednesday morning. The wild swing won’t end there, either, as temperatures are expected to be back into the 80s by the weekend.
That trough is part of the cooler air that was expected to flood the Lower 48. The only problem is that ridging in the eastern U.S. is keeping it bottled up in the west. As that ridge breaks down, Denver’s temps are going to rebound towards the weekend because that trough is ejecting in the form of a cut-off low that’s going to swing through the upper Midwest and into the Northeast. That could bring some rain as far south as Tennessee as we get into next weekend, though we likely won’t see a lot of rain.
There was no single culprit to Denver “stealing” all of our cooler air; it is just a general weather pattern that developed across the continental U.S. But one of its influences is a tropical system that’s parked off the coast of the Carolinas.
This system may ultimately impact the East Coast. For now, it is only given a 10% chance of tropical cyclone development within the next 48 hours by the National Hurricane Center. But as long as this low pressure system is spinning just off the coast, it’s acting as a barricade of sorts. So instead of colder air that’s pouring into the continental U.S. from Canada being able to spill on into the Southeast, it gets bottled up to our west. And the evolution of that trough our west to a closed low pressure system helps pump up the ridge over the eastern U.S.
So instead of being in the 70s or even in the 60s this week, we’re going to be in the mid to upper 80s. Instead of experiencing below-normal temperatures for early September, we’re actually going to be seeing above-normal daily high temps. Humidity levels will remain low for the next couple of days, so it’ll feel pleasant despite the warm temps (and there will be virtually no chances of rain for the next couple of days). But as southerly flows increase under that ridge, humidity levels will increase and it will feel warmer. We’ll also see rain chances increase slightly Thursday and Friday, before better rain chances move in for the weekend.
Here’s what will eventually happen: that storm that’s creating havoc in the Rockies will eventually lift to the north and east, and it’ll drag colder air behind it. That trailing cold front will reach our region by the weekend, which is what will increase rain chances. When that happens, we’ll see cooler temperatures — though the cooldown won’t be as extreme as what we originally expected for this week. We may not get out of the upper 70s by next Monday, one week from today.
When that cold front moves through, it looks like we could be done with 80-degree temps for a while. In fact, if you love fall, cross your fingers that we will be done with 80-degree temps until next spring. The rest of September looks considerably cooler than what we’ll see this week. However, we’ve already seen Mother Nature throw us one curve ball, so do you want to bet against another?
Here’s the thing: tropical weather has a big influence on what our weather is like in this part of the world, and the Atlantic Basin is incredibly active right now. As the above graphic shows, there are three disturbances currently being watched, and two are already tropical storms. For now, it looks like both of those cyclones may stay well away from the continental U.S. But they won’t be the last ones. The long-range GFS shows multiple opportunities for tropical storms beyond these two. And depending on the exact strength and track of any of these storms, they can create pattern changes that drastically impact our weather in Tennessee and the Southeast in general.