578
FXUS63 KJKL 250820
AFDJKL

AREA FORECAST DISCUSSION
National Weather Service Jackson KY
420 AM EDT Wed Sep 25 2024

.KEY MESSAGES...

- Repeated rounds of showers and thunderstorms through Wed night
  could result in heavy rain and isolated flooding.

- The remnants of Helene is forecast to bring a widespread,
  soaking rain event later in the week.

- Flash flooding could result form the remnant of Helene, but the
  potential may be limited by the quick movement of the system.

- High temperatures will average near normal the rest of the
  week.


&&

.UPDATE...
Issued at 945 PM EDT TUE SEP 24 2024

All but a smattering of isolated showers have exited the JKL CWA
as of 140z. Additional rounds of showers, along with some
embedded thunder, can be expected for the overnight as
disturbances stream northeastward ahead of a stalling cold front.
The highest rain chances (50-80 PoP) will be across the two tiers
of counties adjacent to Virginia. Rain chances will be lower
(30-60 PoP) over counties further northwest.

UPDATE Issued at 535 PM EDT TUE SEP 24 2024

Storms should hold together toward the US 23 corridor and the
Severe Thunderstorm Watch 681 has been extended further east.

&&

.SHORT TERM...(This evening through Wednesday night)
Issued at 515 PM EDT TUE SEP 24 2024

Late this afternoon an upper level ridge was centered northeast
of the FL peninsula with another ridge centered in the Great
Basin vicinity. Meanwhile, an upper level trough extended from
central Canada to the upper to mid MS Valley region to the Ozarks
vicinity to TX. At the surface, an area of low pressure was
tracking northwest of the Commonwealth near the southern end of
Lake MI with a frontal zone trailing into western KY to Western TN
to LA. Meanwhile, Helene continues to develop/strengthen in the
Caribbean to the east of the Yucatan. Convection was ongoing
across the region ahead of this system across the Lower OH and in
the Appalachians. Recent mesoanalysis has inhibition remaining
over northeast KY to the WV border with 1000 to 2000 J/kg MLCAPE
across the remainder of the area. Shear is ample with effective in
the 45 to 55KT range. Mid level lapse rates are analyzed at 5.5
to 6C/km with low level lapse rates of 7C/km or stronger in the
southwest.

This evening and tonight, the upper level trough is expected to
remain in place west of the area with the southern end expected
to begin closing off to an upper level low over the mid MS Valley
vicinity. A shortwave trough is progged to pass northwest of
eastern KY this evening. Meanwhile the sfc low should continue
northeast into the Great Lakes through tonight and in Wed as the
upper level trough axis remains west of the area and the upper
level low meanders over the mid MS Valley vicinity. The trailing
cold front should gradually move across western to central KY and
then stall near or west of the area. At the same time, Helene
should track into the northeast Gulf of Mexico.

Convection should peak in coverage through around sunset. MLCAPE
is progged in the 1000 to 1500 J/kg over the next couple hours
with inhibition going away further to the east/northeast. Mid
level lapse rates of 5.5 to not much more than 6C/km if that
should linger into the evening as well while effective shear
should remain in the 40 to 50KT range or so as well. Damaging wind
gusts remain the primary threat with cells this evening though
lower end severe hail could fall from any storms that rotates. A
brief spinup tornado cannot be completely ruled out with an QLCS
structure that may evolve. Instability should wane around or
within an hour or two after sunset, but shower chances will linger
overnight ahead of the boundary and with an upper level trough to
the west of the area. The boundary will remain west of the are on
Wed and into Wed night as well with the upper low west of the
area and unsettled weather should continue.

.LONG TERM...(Thursday night through Tuesday)
Issued at 419 AM EDT WED SEP 25 2024

A very interesting synoptic set up for the extended! Two systems
will come together to impact our weather for the duration of the
period.

First, a strong closed upper level low will be in place across the
Mid-Mississippi Valley, allowing for a deep pull of moisture into
the state. Meanwhile, Tropical Storm Helena will have made landfall
late Thursday, and will continue to push inland and northward. By
the start of the period Thursday night, the two systems will begin
to mesh, starting to rotate counter-clockwise around each other
while sitting over Kentucky and surrounding states. This will
continue until late Friday, at which point they will finally merge
together, again remaining nearly stationary across western KY. The
low center will finally start to shift eastward Saturday night into
Sunday. Models start to diverge in solutions at this point, with the
GFS being more progressive in pulling the system to the east, being
well out of the state by the end of the forecast period, and the
ECMWF keeping it more centered across the Central Appalachians for a
bit longer.

As for sensible weather, with two systems merging right across the
state, it`s no surprise that the amount of lift and moisture, we can
expect lousy weather. Friday will be the best day for pops and heavy
precip as the remnants of Helena rotate through eastern Kentucky.
By the weekend, when the two systems merge, the center of activity
will be more across western Kentucky, so this may be the first break
that we get in eastern KY through the week. That being said, pops
may still be scattered and could lead to precip in some locations.
More widespread pops will move back into the CWA by Sunday as the
consolidated low moves back eastward across eastern KY. By Monday,
kept with the NBM which is a mix of the different model runs. This
will keep pops across the CWA for the remainder of the forecast
period and scattered sky cover, but depending on which model the
forecast starts to trend towards, this could either increase or
decrease.

Given cloud cover through most of the period, this will limit
daytime heating, but also the overnight cooling. It also limits the
amount of ridge/valley temperature differences, along with the fog
potential. Did go ahead and keep some fog mention in for Friday
night, after the heavier rain shifts west of the CWA. Models are
suggesting some potential clearing in the cloud cover from the west,
which could aid in some fog development. Otherwise, did not make too
many changes to the temps or winds from the NBM.

&&

.AVIATION...(For the 06Z TAFS through 06Z Wednesday night)
ISSUED AT 615 AM EDT WED SEP 25 2024

Scattered showers and thunderstorms were ongoing at the start of
the period, bringing localized sub-VFR conditions. Outside of the
precipitation, conditions were mainly VFR. This scenario is
expected to continue through the forecast. That being said, TAF
sites may very well have restrictions at times, but nailing down
timing is too difficult to explicitly state when, and including
sub-VFR conditions would likely result in greatly over-forecasting
poorer conditions. Hence, prevailing VFR is forecast, with the
realization that there will likely be times of sub-VFR conditions.

&&

.JKL WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

UPDATE...GEERTSON
SHORT TERM...JP
LONG TERM...JMW
AVIATION...HAL