326
FXUS64 KMRX 230138 AAC
AFDMRX

Area Forecast Discussion...UPDATED
National Weather Service Morristown TN
938 PM EDT Wed May 22 2024

...New UPDATE...

.UPDATE...
Issued at 931 PM EDT Wed May 22 2024

A weakening MCV over the northern Plateau will move across the
rest of east Tennessee and southern Appalachians this evening
and generally east of the region soon after midnight. Strongest
convection is across southwest Virginia and northeast Tennessee
where modest instability remains. MLCAPES of 1000-1500 with
effective shear of 35kts. Enough instability and shear combo to
produce strong updrafts with some small hail possible over these
areas. DCAPE of 600-700 which is limited but enough for
strong/gusty winds with these storms.

Convective complex will move east with generally mostly cloudy
sky. Lowered temperatures where rain has occurred.

&&

.UPDATE...
Issued at 539 PM EDT Wed May 22 2024

Update to increase the chance of showers and thunderstorms across
much of east Tennessee and southwest Virginia, especially along
and north of interstate 40, for this evening. An area of storms
are quickly moving east toward the northern Plateau.

High winds will be the greatest threat from these storms with
marginal severe hail be possible as well. OHX radar shows over
50kt winds with the storms heading into the northern Plateau.
DCAPE values of 900+ and Derecho Composite Parameter of 2.

As the storms move across the Plateau toward the northern half of
Tennessee and southwest Virginia we expect them to weaken. Airmass
is quite a bit less unstable.

&&

.SHORT TERM...
(This evening through Thursday)
Issued at 308 PM EDT Wed May 22 2024

Key Messages:

1. A few strong to maringally severe storms possible in the northern
Plateau this evening.

2. Another round of potentially strong to severe storms is expected
Thursday from late morning through early afternoon, mainly north of
I-40. Potential for training storms will pose a flooding threat.

Discussion:

A line of strong to severe storms streches along a pre-frontal
trough from central KY to West TN. Mesoanalysis of the region shows
a much les favorable environment for severe over our area, with CIN
keeping convection capped and weak deep layer shear. The HRRR and
ARW are in good agreement with the progression of storms across
Middle TN through the afternoon, and show them reaching our Plateau
counties around 00-01Z. By the time they reach I-75, the storms
weaken quickly and have virtually dissipated before reaching Tri-
Cities. The forecast for the evening will have likely PoPs only in
Morgan/Scott counties, dropping to a chance in SW VA and NE TN by
midnight. This activity should end around 06-08Z once the shortwave
trough exits, but another stronger trough will be approaching from
the west.

Convection is expected to develop tomorrow morning to our west in
association with this trough and upper jet streak. The CAMS are not
in good agreement on the details of the evolution of this
convection, but the general trend appears to be showers and
thunderstorms moving into the Plateau area during the mid to late
morning hours, about 12-16Z, and crossing the TN Valley through the
early afternoon. Some additional development may occur behind this
initial activity during the mid to late afternoon. Given the model
disagreements, PoPs have been cut back from categorical, except in
SW VA where confidence is highest. CAPE values of will support some
strong to severe storms, but deep shear is rather weak. A marginal
wind threat is possible, and given the unidirectional winds and
expected storms in the same area this evening, training of storms
may pose a threat of flooding in some isolated locations.

&&

.LONG TERM...
(Thursday night through next Wednesday)
Issued at 308 PM EDT Wed May 22 2024

Key Messages:

1. An unsettled period with multiple rounds of showers and
thunderstorms for the period.

2. Some of the storms may be strong to severe at times, with the
higher chances for severe storms looking like the weekend and
possibly into Monday. Localized flooding will also be possible.

Discussion:

The period begins with flat ridging over the Gulf and a series of
upper lows over the northern plains. These conflicting sets of
features will meet overhead, contributing to disturbances that will
move in the zonal flow over us to bring convection-triggering
convective rounds for the rest of this week.

By Sunday, that northern parade of troughs will orient somewhat
further south, and begin the process of what will become a deepening
Great Lakes upper low which will usher a cold-frontal line of
convection through the area around Monday morning. This frontal
convection might be the primary risk for organized severe convection
for the period...otherwise a little something here or there is
possible on other days.

No day in particular has impressive QPF, but the repeated rainfall
will tilt the risk of excessive rainfall and localized flooding
upward by week`s end, and that will probably carry over through the
frontal passage event Monday morning.

Afterward, that 500MB low over the Great Lakes will deepen as it
slowly rolls eastward, and we look to end up on the northwest-flow
side of an omega-pattern central U.S. ridge. This will create
potential for additional disturbance-driven rounds of scattered
precip Tuesday and Wednesday, moreso around VA, before the blocking

&&

.AVIATION...
(00Z TAFS)
Issued at 632 PM EDT Wed May 22 2024

A line of showers and thunderstorms will move into the TRI and TYS
airports this evening. These storms will be weakening as the
atmosphere is more stable across the Tennessee valley. The storms
may move just north of the CHA airport.

For the rest of tonight, convection will move east and weaken by
midnight with plenty of clouds remaining mainly VFR conditions but
can not rule out a potential of scattered 1 kft clouds.

For Thursday, scattered convection will redevelop especially in
the afternoon at all TAF sites.

&&

.PRELIMINARY POINT TEMPS/POPS...
Chattanooga Airport, TN             68  86  67  83 /  20  30  40  60
Knoxville McGhee Tyson Airport, TN  67  80  64  79 /  40  60  50  70
Oak Ridge, TN                       65  80  63  79 /  70  60  50  70
Tri Cities Airport, TN              62  78  61  79 /  60  80  50  70

&&

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

$$

SHORT TERM...DH
LONG TERM....GC
AVIATION...DH