Storms are certain next Wednesday…but how severe will they be?

After taking the weekend off to enjoy a bit of family time, enjoy the springtime weather, and let the models catch up to this system, it’s time to jump back in it. Data is still spread concerning the more finer-scale issues (instability, wind shear, moisture return), but most of the more “popular” model suites have all hit upon the same basic evolution of the upper level trough. There still could be some shifts and dips, but wholesale changes, IMO, are pretty much done.

Virtually all model suites – GFS, NAM, European, SREF – paint a powerful QLCS through the area with an estimated ETA overnight into the morning on Thursday for the Nashville area. Given the overnight arrival for the area, the overall significant tornado threat will be minimized.

However, that’s not to say there WON’T be a tornado threat. Instability values look to wane as the night progresses (starting out with ~1500j/kg, but dips to 500-750j/kg across West TN and about the same for us), but a 50kt low-level jet ramps up during frontal passage. Combine that with ~50kt worth of 0-6km bulk shear (a measure of atmospheric “turning”, any convective complex that can become sufficiently rooted near the surface could rotate.

I know there was earlier discussions about a warm sector tornado outbreak, but I just don’t see the evidence for that right now. If temperatures and dew point values verify, the LCLs (cloud bases) will be a tad bit higher than I’d like to see them and capping issues will undoubtedly be an issue given the lack of lower level forcing needed to effectively erode the cap. I think this will still be an issue even if a secondary surface low forms given the rather close proximity of it’s progged location. Shear and surface convergence will surely increase, but there just won’t be enough time between cyclogenesis and it’s passing to have much impact.

Bottom line, I expect a loud and robust QLCS – squall line – (there could even be some embedded supercellular-like structures) with an attendant tornado chance. Wind fields don’t look too impressive, so the damaging wind threat looks to be mitigated, except for thunderstorm wind gusts. Don’t think hail is going to be an issue given the meager instability values. We’ll see how the models play this all out over the next 48 hours, and I reserve the right to change my thoughts given any changes.

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