440
FXUS64 KMRX 211133
AFDMRX

Area Forecast Discussion
National Weather Service Morristown TN
733 AM EDT Mon Sep 21 2026

...New AVIATION...

.KEY MESSAGES...
Updated at 724 AM EDT Mon Sep 21 2026

- Well above normal temperatures to persist through Tuesday. But relief
  is on the way, with a pattern change expected mid-week and much
  cooler temperatures to follow.

- Scattered to numerous showers are expected Monday through
  Wednesday.

- A few strong to severe storm with damaging winds could occur
  Monday, with damaging winds being the primary threat. Localized
  flooding will be possible each day through Wednesday as well.

&&

.DISCUSSION...
Issued at 123 AM EDT Mon Sep 21 2026

A weak shortwave will move into the Ohio valley during the day
Monday and then push east of the forecast area by Tuesday morning,
all of which is ahead of a closed upper low shifting east through
the northern plains and into the Upper Midwest. At the surface, this
wave will push a weak cold front towards the Tennessee valley during
the day, lingering just to our west and northwest Monday night
through Tuesday. As such, expect this to be a focus for increased
convective coverage both Monday and Tuesday. Forecast soundings show
enough instability to be concerned about a few strong to severe
storms on Monday capable of damaging winds. The overall threat isn`t
high, but the combination of decent instability along with high
PWATs means that a few damaging wind gusts similar to what was seen
a day or two ago could occur. Additionally, with slow storm motions,
some isolated flash flooding could occur. Tuesday will be similar in
coverage as the Ohio valley upper low begins to shift southeast, but
instability will be notably less so outside of the far southern
parts of the area, think that any severe threat is low.

Regardless of the expected storms for Monday and Tuesday, the heat
will continue. Highs in the 80s and 90s are expected.

On Wednesday the pattern change gets underway and we begin to see a
break in the relentless heat. By Wednesday a rex block pattern takes
shape as an upper ridge builds over the Canadian side of the Great
Lakes region, and the aforementioned Ohio valley upper low deepens
over the Ohio valley and central Appalachian region. With the upper
low to our north and NW flow aloft, this will push the cold front
through the southern Appalachians and allow the cooldown to begin.
By Thursday through the weekend we should see highs topping out only
in the 70`s for every except southeast TN where they may squeak
across the 80 degree mark. This pattern will also be fairly dry with
a more Canadian airmass moving in.

&&

.AVIATION...
(12Z TAFS)
Issued at 724 AM EDT Mon Sep 21 2026

A cluster of thunderstorms has developed from CHA to just SW of
TYS. These showers and storms should stay in the vicinity to
start the TAF before exiting both terminals by 13Z. I have opted
to cover this with VCTS at TYS and VCSH at CHA. Fog at TRI has
begun to improve and all sites should return to VFR by 13Z.

The primary concern will be this afternoon`s showers and
thunderstorms that develop after 18-19z. I have maintained a
several hour PROB30 for SHRA, but in all likelihood an hour or two
within that period will likely experience TSRA similar to the
previous few days. Showers and thunderstorms are expected to wrap
up by 01Z this evening, but a few isolated showers may linger a
bit longer. All sites will return to VFR this evening with
scattered mid-high level clouds tonight.


&&

.PRELIMINARY POINT TEMPS/POPS...
Chattanooga Airport, TN             94  71  92  69 /  50  40  70  40
Knoxville McGhee Tyson Airport, TN  92  69  89  67 /  30  40  80  70
Oak Ridge, TN                       91  68  87  66 /  40  40  70  60
Tri Cities Airport, TN              88  65  83  63 /  30  60  80  70

&&

.MRX WATCHES/WARNINGS/ADVISORIES...
NC...NONE.
TN...NONE.
VA...NONE.
&&

$$

DISCUSSION...CD
AVIATION...BH