Loss Of Instability
Thursday, August 20, 2026 · 11:24 AM
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There is a marginal risk, level one out of five, for severe storms for this afternoon and evening mainly south of Interstate forty and along the Cumberland Plateau. Damaging winds are the main concern. Drier with slightly below normal temperatures this weekend, especially overnight, then near normal temperatures mid next week. Clearing from the west! Rebound in the heat! Moisture lingering in the air! Morning storms are gone but the sky is primed! High Resolution Ensemble Forecast points to afternoon fire! Shortwave pushing out of Missouri, cutting through the sky! South of Interstate forty, convective initiation takes hold! Quarter size hail in the mid-level lapse rates! Outflows evolving, drifting back to the north! FIFTY DEGREES! FIFTY DEGREES! FIFTY DEGREES! MOVE SOUTH! The boundary is waiting, the shortwave swings through! Damaging wind gusts tearing us in two! By nine P.M. the sky begins to freeze! Fading away with the loss of instability! Troff axis taking over! Cooler! Stable! Light northwesterly breeze! OPEN UP THE PIT FOR THE TROFF AXIS! FIFTY DEGREES! FIFTY DEGREES! FIFTY DEGREES! COOLER AIR! Loss of instability! Fading away! It is over by nine P.M.!
The forecast discussion
NEW SHORT TERM, LONG TERM
KEY MESSAGES
Updated at 1120 AM CDT Thu Aug 20 2026
- There's a marginal risk (level 1 out of 5) for severe storms for this afternoon and evening mainly south of I-40 and along the Cumberland Plateau.
Damaging winds are the main concern.
- Drier with slightly below-normal temperatures this weekend, especially overnight, then near-normal temperatures mid next week.
SHORT TERM
(Rest of today through Friday) Issued at 1120 AM CDT Thu Aug 20 2026
The morning complex of thunderstorms has dissipated across Middle Tennessee with only a few lingering showers evident on radar at this time.
Skies are clearing from west to east and we should get a good rebound in temperatures toward early afternoon.
It will also be somewhat humid given all the rainfall this morning.
That said, HREF members all point toward additional afternoon storms developing for areas generally along/south of Interstate 40. It's here where a boundary is depicted which will play a role in convective initiation in addition to an approaching shortwave disturbance (currently over Missouri).
A few storms could be strong to severe mainly posing a threat for damaging wind gusts or perhaps hail up to quarter size given better mid-level lapse rates south of I-40. Winds aloft should promote storm progression to the southeast, but depending on how outflows evolve, there could be some activity that drifts north and/or persists into the evening hours.
The shortwave swinging through may keep a little activity going as well, but severe threats should diminish by ~9 PM with loss of instability.
Middle Tennessee will sit more into the trough axis tomorrow, so cooler and more stable conditions are forecast with a light northwesterly breeze.
LONG TERM
(Friday Night through next Thursday) Issued at 1120 AM CDT Thu Aug 20 2026
Weather conditions look very good across the region this weekend with influence of the trough remaining in place.
Currently forecast temperatures are a few degrees below normal, more so for overnight lows in the low to mid 60s west of the Plateau.
We have some 50s across the higher terrain Monday and Tuesday mornings.
Broad northwesterly flow aloft will provide a corridor for passing shortwaves mid next week, so PoPs are generally 20-40% at the end of the forecast period.