555
FXUS64 KMRX 212343
AFDMRX

Area Forecast Discussion
National Weather Service Morristown TN
743 PM EDT Tue Jul 21 2026

...New AVIATION...

.KEY MESSAGES...
Updated at 730 PM EDT Tue Jul 21 2026

- Showers and storms will affect the area tonight into at least
  Wednesday night. Some of the storms this evening into the first
  part of tonight may be strong to severe with damaging winds the
  primary threat along with a low end possibility of a tornado
  mainly across the northern portions of the area.

- Very heavy rainfall will be possible with a threat of flash
  flooding tonight through Wednesday night, with the primary
  threat mainly northern half or two thirds of the area tonight
  into Wednesday with the threat then shifting southward by
  Wednesday night.

- Below normal high temperatures can be expected Thursday through
  Saturday, then temperatures will not be far from normal for the
  remainder of the period.

&&

.DISCUSSION...
Issued at 210 PM EDT Tue Jul 21 2026

There is still uncertainty in the details for the tonight through
Wednesday night time frame although the envelope of model
solutions is narrowing a bit overall as we get closer. Weak short
wave energy will be moving through the northeast CONUS upper
trough and a summertime cold front will sag southeast toward our
area tonight. With the core of the upper jet staying well to our
north, the upper support over our area looks weak overall. This
leaves us with a less certain scenario more dependent on the
timing/location of the summertime front (which is as usual quite
difficult to pinpoint in advance) as well as the evolution and
movement of upstream convection and related outflow
boundaries/cold pool dynamics. That being said, the main two
concerns in the short term continue to be the potential for severe
storms and also flash flooding.

The potential for severe storms still looks to be highest across our
northern areas this evening into tonight.  Most of the CAMS show a
broken line of convection dropping out of KY this evening but
weakening as it moves into our area, with some showing a westward
development of the stronger cells following the gradient of higher
CAPE which is a plausible scenario. How well convection maintains
itself will be critical for our severe threat and is still unclear.
The more significant effective bulk shear (around 30 to 40 kts and
possibly even briefly higher north) will be across the northern half
of our area , and low level hodographs show enough of a clockwise
curve to keep the low end threat of a tornado in place providing the
convection maintains enough strength. The primary severe threat
still looks to be damaging winds. Our northern counties will be the
first to be impacted and given the expected weakening trend, would
thus be facing the higher severe threat.  Also, with the potential
for a pivot to the west for the stronger storms our northern Plateau
counties would be another location that may see a higher threat.
However, strong to severe storms may push well into our area
overnight if the weakening trend is slower than most CAMS currently
depict.

As for the flooding threat tonight through Wednesday night, models
continue to indicate moisture will be plentiful with PWAT values
either side of 2 inches for much of the period and CAPE generally
exhibiting a tall skinny profile which would favor warm rain
processes and high rainfall rates. Placement of convective
boundaries and eventually the frontal boundary that will move in but
be slow to exit will play a large part in location and timing of the
heavy rain threat.  Hi-res ensemble data is pointing toward a threat
of heavy rain across northern half or two thirds of our area tonight
into Wednesday as the northern convection pushes in and likely
leaves a residual boundary, and then the front itself pushes in
Wednesday. Both the HREF and REFS show bands of very heavy rainfall
somewhere across our northern half, with potential for 3 to 5+
inches in some spots tonight through Wednesday. The precipitation
focus then shifts further south by Wednesday night as the front
slowly sags southward. Given the expected slow boundary movement,
training cells will be a concern and this combined with the fact
that the ground is still on the wet side across portions of the area
from recent rains and flooding, will issue a flash flood watch for
roughly the northern two thirds of our area for tonight and
Wednesday.  Will let later shifts look at whether or not an
additional watch is needed for southern areas as the threat shifts
south. It is possible that the flooding threat will linger into
Thursday across the south as the front struggles to push south of
our area although northern areas will likely be mainly dry.

The remainder of the forecast has the basic pattern of upper ridging
to our west and troughing over the eastern CONUS continuing.  We
will see short wave energy moving southeast on the back side of the
trough at times that will bring additional showers an storms to our
area for the Friday through Tuesday period.  Timing of these
features and the resulting convection is of course unclear this far
out. Temperatures for Thursday into Saturday look to be a bit below
normal, then the remainder of the period through Tuesday will likely
see temperatures not far from normal for this time of year.

&&

.AVIATION...
(00Z TAFS)
Issued at 730 PM EDT Tue Jul 21 2026

A line of thunderstorms is moving into the region over the next
few hours from the north. This line is expected to weaken as it
moves into the region. Chances of thunder at each terminal
overnight is low but rain is likely at times. Scattered showers
will continue through the morning hours and all afternoon tomorrow.
Thunder will likely be more isolated. MVFR CIGs and possibly vis
will be possible mainly at TRI in the late night and morning
hours. Low level wind shear is possible in the late night and early
morning hours near TRI but confidence is low.

&&

.PRELIMINARY POINT TEMPS/POPS...
Chattanooga Airport, TN             76  89  71  86 /  20  60  60  50
Knoxville McGhee Tyson Airport, TN  74  86  68  84 /  60  80  70  40
Oak Ridge, TN                       73  86  66  84 /  70  70  50  20
Tri Cities Airport, TN              70  82  64  82 / 100  90  50  30

&&

.MRX WATCHES/WARNINGS/ADVISORIES...
NC...NONE.
TN...Flood Watch from midnight EDT tonight through Wednesday evening
     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 from midnight EDT tonight through Wednesday evening
     for Lee-Russell-Scott VA-Washington VA-Wise.

&&

$$

DISCUSSION...99
AVIATION...McD