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