516 
FXUS64 KMRX 121737
AFDMRX

Area Forecast Discussion
National Weather Service Morristown TN
137 PM EDT Wed Aug 12 2026

...New DISCUSSION, AVIATION...

.KEY MESSAGES...
Updated at 135 PM EDT Wed Aug 12 2026

- Isolated scattered showers and storms this afternoon. Low confidence
  in coverage. Flooding and isolated damaging wind gusts will be 
  the main threats. Another round possible this evening and 
  overnight.

- Shower and storm chances continue through Friday and there is
  still at least some potential for a few storms to become strong
  to severe each day, with damaging winds and localized flooding 
  the main threats. 

- Temperatures increase Friday and into weekend. Heat Advisory 
  products may be needed. 

&&

.DISCUSSION...
Issued at 135 PM EDT Wed Aug 12 2026

An interesting forecast in the near term; how it exactly plays out 
is very uncertain. A decaying overnight/early morning MCS made it's 
way down from KY this morning. This has produced a residual outflow 
boundary and thermal gradient across our area. This gradient runs 
from northwest to southeast, from the Northern Cumberland Plateau 
down through the east TN Valley (generally along and around I-40). 
Areas to the north and northeast (northeast TN and southwest VA) are 
more stable due to the rain cooled air from earlier. Areas to the 
south and southwest (generally along and south of I-40) will 
continue to become increasingly more unstable through the afternoon. 
Though the environment is characterized as moist with moderate/high 
MLCAPES, low and mid level lapse rates aren't too impressive at 
around 6 to 6.5C/km. However, the outflow/thermal gradient, may 
serve as a forcing mechanism for convective development this 
afternoon. CAMs and a few deterministic models latch onto this idea, 
but model placement and coverage of the convection varies. I feel 
fairly confident that there will be at least some isolated 
convection, especially near the outflow/gradient. But how widespread 
is uncertain. 

The main impacts with the afternoon convection will be isolated 
damaging wind gusts and flooding. Some localized 2 to 3 inch 
rainfall amounts are expected, with possibly locally higher amounts. 
The main question is once again, how widespread is the convection. 
If these localized 2 to 3 inch rainfall amounts occur over areas 
that had heavy rain yesterday, where there is any overlap, flooding 
is very likely. There is also some low-end effective bulk shear 
present through the afternoon at around 20kts. If we see convection, 
it wouldn't surprise me to see some weak midlevel rotation in any 
stronger storm. 

Then, all eyes turn toward the evening and overnight activity. An 
MCS is forecast to move through Indiana and down through KY late 
afternoon early evening. The question is, how strong will this MCS 
be when it enters our area by mid to late evening. It really just 
depends on how established this system is and if a strong cold pool 
can developed and remain balanced with the MCS in order to continue 
propagation. Model solutions widely vary. Some show a decent line of 
storms moving into the area from the north this evening and some 
models show nothing. Flooding and isolated damaging wind gusts will 
continue to be the main concern if we see these storms enter from 
the north. Additional overnight redevelopment is also possible along 
any outflow the evening MCS may leave behind.

Due to the continued threat of flooding, though confidence on 
convective coverage is low, will extend the existing flood watch 
through Thursday morning to account for any convection this 
afternoon, evening, and overnight. Will also expand it to include 
Loudon, Roane, and Anderson counties.

Additional periods of showers and storms are possible Thursday and 
Friday. The shortwaves look to be relatively weaker so the potential 
for strong/svr storms seems relatively lower, though not zero. We 
will also start to see an increase in upper-level heights by Friday 
and this will translate to a slight warming trend. Central and 
southern areas may be looking at Heat Advisory criteria as we head 
into this late week/weekend period. While we cannot totally rule out 
some diurnal pops, additional organized convection is unlikely. This 
pattern is expected to continue into next week extent but perhaps 
with temperatures a few degrees cooler comparative to the weekend.

&&

.AVIATION...
(18Z TAFS)
Issued at 135 PM EDT Wed Aug 12 2026

Another lower confidence period given the uncertain evolution of 
ongoing convection upstream over the Ohio Valley. TSRA redevelops 
across the plateau and SE TN this afternoon and early evening. I've 
tweaked the timing of the PROB30 group for KCHA and opted to leave 
it VFR & dry overnight as the second round of TSRA should remain to 
the north of the terminal. Morning convection over NE TN/SW VA has 
dissipated and left a stable layer across that area. This should 
result in VFR conditions through early-evening at KTRI. An 
additional round of TS will move into NE TN/SW VA this evening 
around 03Z. I have maintained a PROB30 for this potential at KTRI. 
There's uncertainty in how well this round will hold together as it 
treks to the SSE, so I have opted to leave KCHA VFR overnight.
This leaves KTYS with the potential for two rounds of TS: one late 
this afternoon and early evening then a second round of TSRA late 
evening into the overnight period. I have included two PROB30 groups 
for TSRA as confidence is not high enough for a prevailing or TEMPO 
group. Expect Mostly VFR this period, with occasional MVFR 
conditions in convection. There is a non-zero chance of BR/FG 
development at KTRI if they're able to clear out by daybreak.

&&

.PRELIMINARY POINT TEMPS/POPS...
Chattanooga Airport, TN             74  95  75  97 /  20  30   0  10 
Knoxville McGhee Tyson Airport, TN  73  92  76  94 /  50  40  10  30 
Oak Ridge, TN                       72  92  74  94 /  40  40  10  20 
Tri Cities Airport, TN              69  88  71  89 /  40  40  20  50 

&&

.MRX WATCHES/WARNINGS/ADVISORIES...
NC...NONE.
TN...Flood Watch through Thursday morning for Anderson-Blount Smoky 
     Mountains-Campbell-Claiborne-Cocke Smoky Mountains-Grainger-
     Hamblen-Hancock-Hawkins-Jefferson-Johnson-Knox-Loudon-
     Morgan-North Sevier-Northwest Blount-Northwest Carter-
     Northwest Cocke-Northwest Greene-Roane-Scott TN-Sevier 
     Smoky Mountains-Southeast Carter-Southeast Greene-Sullivan-
     Unicoi-Union-Washington TN.

VA...Flood Watch through Thursday morning for Lee-Russell-Scott VA-
     Washington VA-Wise.

&&

$$

DISCUSSION...99
AVIATION...BH


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