Plaincast

Messages

Scattered showers and storms are expected early Monday morning, mainly west and southwest of Knoxville. Brief bouts of strong winds and heavy rainfall are possible.

Two potential rounds on Tuesday, one in the morning and again in the late afternoon. Low confidence regarding any storms Tuesday morning. At this time, Tuesday afternoon and evening holds the greatest potential to have a few strong to severe storms with strong to severe winds the primary hazard.

Tomorrow and Tuesday will be the hottest days of the week as heat indices in the mid 90s to low 100s become more commonplace, especially in the central and southern valley.

Discussion

Periods of showers and thunderstorms expected to continue underneath an increasingly oppressive ridge the next couple of days. A few of these storms may be strong to severe, more on that in a moment.

Beginning of the work week features temperatures aloft warming a couple more degrees, this translates to hotter temperatures at the surface during peak heating. Coupled with westerly flow advecting a higher moisture content airmass, heat indices will climb to near 100F tomorrow and into the low 100sF on Tuesday. Not out of the question to hit heat advisory criteria on Tuesday but would need clouds to work out and higher surface moisture than guidance currently depicts. Blended lower dewpoint values into the forecast since the the blend-of-models forecast typically overdoes dewpoints against the ASOS calibrated measurements.

As far as storms, we have several potential rounds. With each round potentially yielding further downstream consequences for the forecast like a line of dominoes, just know the inherent uncertainty of summertime convection is still present.

First round is overnight tonight into early Monday morning. The the high-res rapid-refresh model has been the most consistent, showing for a while now the potential for the overnight MCS blasting through Middle Tennessee and southward. Other CAMs have been in support in varying degrees, although there's still variance in exact timing. Other than storms existing, the important question is the degree of SBCAPE available to the presumed thunderstorm complex, with the HREF at least suggestive of at least 1000J of storm energy available as the storm complex moves through Tennessee overnight. There's also questions of eastern extent, SPC recently updated the Level 1 wind risk as far east as Knox and Cherokee Counties, which the the regional model would agree with. The more likely locations lie along the Cumberland Plateau. Should the surface inversion not be too strong, gusty winds will occur, along with brief heavy rainfall.

Once the morning storms move out Monday itself is likely to be quiet with no forcing or lost MCS wandering through. The next storm complex may, or may not occur, on Tuesday morning. Some guidance, like the RRFS and the high res the regional model, depict the Tuesday MCS dying on our door mat along the Kentucky/Virginia borders. Contrast this with the 12z the high-res rapid-refresh model which brings another MCS clean into the bulk of the region Tuesday morning. This system, if materialized, would also have a risk for wet gusty winds and heavy rains. It will also play a significant role in the degree to which we'll be able to destabilize heading into Tuesday afternoon.

Depending on remaining cloud debris on Tuesday, and the amount of sunny skies we can recover back to, will help determine how much storm energy can build in the summer skies ahead of the incoming cold front. Kinematically there's a lot going in favor of severe storms on Tuesday, especially the further northeast you go. Deep layer bulk shear is 40 to 50 knots, which given this time of year is the climatological minimum for shear, means we have plenty of shear. The the American global model doesn't seem too impressed, which is likely chalked up to complications from morning storms. Should the area have everything line up with timing of the front, the strong kinematics, and ample amounts of storm energy heading into Tuesday afternoon, then we'll be primed for an all-hazard threat profile. Tornado is the lower end of the risks, also the easiest to get wiped out depending on what happens Tuesday morning, but the 0-1 shear profiles and possibility of fully mixing back out means we have to consider it. If we get strong and deep supercells, then severe hail in northeastern TN into southwestern VA is likely. Damaging winds is the main risk, with guidance depicting enough dry air between 700 and 500 mb plus a fairly saturated profile overall to prompt DCAPE to above 1000J, indicating severe wind risks. Timing for the main threat of the week would be Tuesday afternoon into Tuesday evening, possibly a fairly narrow window once we get closer.