The 140-characters-or-less version of our severe weather potential over the next few days is what I posted on Twitter early this morning:
It’s obviously MUCH more complicated than that, so let’s get into some details…
We could see thunderstorms developing this afternoon and this evening, especially to the northwest of Nashville. That’s the big question mark — will the storms even develop? Any baby shower that wants to grow into an adult thunderstorm will have to break through a “cap” overhead…that’s a layer of warm air about a mile off the ground that will try to suppress such development. Think of it as whack-a-mole, but with thermodynamics.
As usual, the forecast models disagree on whether the storms develop in the first place, and on where they’ll develop.
The HRRR model (left) looks kinda apocalyptic, with the dividing line between “lots of storms” and “what storms?” lining up along I-40. The RPM model (right) moves the greatest threat just slightly farther north:
There are other models that keep the lid on the atmosphere and don’t develop ANYTHING. That’s obviously the best-case scenario. Considering all of the model output, here’s my estimate of storm chances across the Midstate:
If (all-caps IF) those storms develop, they would quickly become severe, with large hail, damaging winds, and even isolated tornadoes possible:
The Storm Prediction Center’s outlook for today really demonstrates the tricky nature of the forecast. The greatest threat (Enhanced Risk, level 3 of 5) includes northwestern Middle Tennessee and most of southern Kentucky:
Look at how fast that threat tapers off! If you were driving east on I-24, you’d go from a significant severe weather threat to virtually ZERO severe weather threat in less than an hour. That’s why, in a demonstration of brutal honesty, I’ve evaluated my forecast confidence as “low.” We just won’t know when, where or even IF storms will develop until they’re actually popping up.
Breaking down the SPC outlooks more specifically, they’re estimating these chances of large hail (1″+) within 25 miles of any point in the shaded areas:
These are the odds of damaging winds (60+mph):
And these are the estimated odds of a tornado:
Don’t cancel anything outdoors, but definitely plan on staying weather-aware — I’ll have updates on Twitter (and a few on Facebook) throughout the day, and of course we’ll have our regularly-scheduled newscasts at noon and again beginning at 4pm.
All the models agree that no matter where the storms initially develop, the storm threat will shift north to along the Ohio River overnight. So we’ll dry out tonight, but it will be steamy for the marathon tomorrow morning:
The first half of the weekend will be just plain hot, with highs in the upper 80s:
Saturday’s record is 90, and we’ll be awfully close. Still muggy, too.
Another round of strong to severe storms will head our way late Sunday. We’re more-confident in the rain chances overall:
But the severe ingredients are looking more borderline at this point. The greatest threat should take shape near the Tennessee River:
Stay plugged-into the forecast over the weekend as that next threat evolves.
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