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515
FXUS64 KMRX 182335
AFDMRX

Area Forecast Discussion
National Weather Service Morristown TN
735 PM EDT Sat May 18 2024

...New UPDATE, AVIATION...

.UPDATE...
-- Changed Discussion --
Issued at 730 PM EDT Sat May 18 2024

Scattered showers and thunderstorms beginning to decrease in
coverage and intensity across the forecast area early this
evening. Still some storms in the Smokies, northeast Tennessee,
southeast Tennessee and southwest North Carolina. Pockets of heavy
rain remain on the plateau and southwest Virginia. As upper level
trough slides east into VA and NC and the sun sets showers and
storms will continue to decrease becoming more widely scattered
and mostly southern half of the area. These showers should end
around 6 AM to 8 Am in the morning. Doing a quick update for
temperatures, dew points and rain chances as convection decreases.
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&&

.SHORT TERM...
(This evening through Sunday)
Issued at 306 PM EDT Sat May 18 2024

Key Messages:

1. Scattered showers and storms through this evening. A few
strong to severe storms are possible.

2. Patchy fog expected tonight.

3. Most locations dry on Sunday, but showers and storms will linger
across the east TN mountains and foothills.

Discussion:

Scattered showers and storms are ongoing across our area as a
weak shortwave/trough is moving in from the west. A few storms may
become strong to severe as instability has risen since the
morning hours. SPC meso page shows roughly 1500 to 2000 J/kg of
SBCAPE. Effective shear is weak at only 20 to 30 kts, but just
enough to perhaps maintain a few stronger updrafts. The main
threats with any stronger storm will be 0.5 to 1" hail along with
strong and gusty winds up to 60 mph. The coverage of showers and
storms should be more isolated north of I-40. Higher coverage is
anticipated down across the southern Cumberland Plateau, southern
TN Valley and southwest NC. This is where the best forcing will
be, along the leading edge of the vortmax. A secondary threat to
monitor will be the potential for isolated flooding if we see any
areas get repeatedly hit by showers and storms as PW values are
around the 90% for this time of year, which increases the heavy
rainfall threat.

Coverage of showers and storms should decrease this evening with
loss of daytime heating, with precip mostly finished by midnight.
Patchy fog is expected tonight, especially across any area that
receives rain today. Tomorrow should be much drier for most of the
area as the trough axis will be centered along the spine of the
Appalachian and eastward. However, this does mean that the east TN
mountains and foothills will likely see showers and storms
through the afternoon hours but non-severe.

&&

.LONG TERM...
(Sunday night through next Saturday)
Issued at 306 PM EDT Sat May 18 2024

Key Messages:

1. Drier and warmer on Monday and Tuesday.

2. Daily chances of showers and thunderstorms to resume Wednesday
onwards, with a warm and humid airmass in place.

Discussion:

Upper level ridging and surface high pressure will begin to impact
the region Sunday night into Tuesday as mostly dry conditions are
expected. However, as we continue to approach the summer months with
an increasing sun angle, strong surface heating will bring us more
towards our typical pattern where a few orographic induced diurnal
showers/storms may be possible. This will generally be the case both
Monday and Tuesday. Temperatures will run near to slightly above
normal into the mid-week.

By Wednesday broad upper level troughing will span across the
northern CONUS as bouts of shortwave energy move through the mean
flow aloft. A surface cold front will extend from an associated
surface low over the northwestern Great Lakes region southwestward
into the southern plains. Recent model trends suggest that this
front will slow down and wash out as it approaches our forecast
area. As such, ensemble guidance suggest probabilities of 24 hour
measurable precipitation on Wednesday have fallen to around 10-30%
where as for Thursday values are closer to the 70-90% range.
Wednesday may not remain totally dry but Thursday & Thursday night
is trending the better day for precipitation at this time.
Precipitation chances are expected to persist into Friday as a more
potent but quick moving shortwave traverses across the Mississippi
river valley through the Tennessee Valley. Warm temperatures and
continued moisture availability will lingering additional isolated
to scattered chances of diurnal activity over the weekend.

&&

.AVIATION...
-- Changed Discussion --
(00Z TAFS)
Issued at 730 PM EDT Sat May 18 2024

Scattered showers and storms are beginning to decrease this
evening. Another hour of vicinity storms at TRI and TYS and until
02Z near CHA but overall VFR conditions through this evening
except for when/if a shower or storm passes over a terminal in the
next hour or two. Later tonight expect MVFR conditions at TYS and
TRI with VFR conditions again by mid to late morning. Also have a
few hours of IFR conditions at TRI around sunrise due to low
ceilings and fog.
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&&

.PRELIMINARY POINT TEMPS/POPS...
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Chattanooga Airport, TN             64  85  63  86 /  50  20  20  10
Knoxville McGhee Tyson Airport, TN  62  81  60  83 /  40  20  10  20
Oak Ridge, TN                       61  82  60  85 /  30  20  10  20
Tri Cities Airport, TN              60  79  56  82 /  40  30  20  10
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&&

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

$$

SHORT TERM...TD
LONG TERM....KRS
AVIATION...TD