596
FXUS63 KJKL 250019
AFDJKL

AREA FORECAST DISCUSSION
National Weather Service Jackson KY
819 PM EDT Tue Sep 24 2024

.KEY MESSAGES...

- Through this evening, some thunderstorms could become severe
  and produce strong wind gusts and hail.

- 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 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 trialing
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 through Tuesday)
Issued at 435 PM EDT TUE SEP 24 2024

The period is expected to begin with an upper level low centered
not far from the confluence of the OH and MS Rivers with an upper
level ridge centered between Bermuda and Bahamas and extending
north across parts of the western Atlantic with another upper
level ridge centered in NM and extending north northeast to the
Northern Plains/Upper MS valley to western Ontario. Meanwhile,
Helene which should be a Major Hurricane as the period begins is
expected to initially be centered over the eastern Gulf of Mexico.
Meanwhile, a frontal zone should initially be in place from
Quebec to the upper OH valley to the Commonwealth to AL to the
northwestern Gulf of Mexico.

The period is expected to initially be dominated by the upper
level low as it interacts with Helene and Helene merges with it to
begin the weekend. The upper level low center should drift south
southwest to the Lower MS Valley Thu to Thu night and then meander
to the mid MS Valley on Sat. After Helene tracks into the
Conus, upper level ridging should build southwest into the
eastern Gulf of Mexico and become centered nearer to the Bahamas
while upper level ridging is progged to retrograde west to the
Four Corners region/Southwest to upper MS Valley. The upper level
low should continue to meander near the Lower OH Valley region to
end the weekend before weakening to an open wave and merging with
a shortwave trough crossing southern Canada to end the period.

Helene will transport moisture into the Southern Appalachians and
the Commonwealth with PW climbing from about 1.4 to 1.6 inch range
early Thu to 1.9 to 2 inches on Thu night per 12Z LREF mean. PW in
the 1.9 to 2 inch range per 12Z LREF mean should remain early on
Friday before decreasing from the southeast on Friday to Friday
night as the remnant low tracks across the Southern Appalachians
and toward the Commonwealth/OH Valley. A widespread soaking rain
should result across the region with the heaviest rain generally
anticipated in the southwest/Cumberland River Basin in the
southwest to near Black Mountain. The threat for the heaviest rain
and perhaps flash flooding appears greatest from late Thu into Fri
morning with WPC having a Marginal to Slight ERO during those
timeframe.

NBM deterministic wind speed and wind gust magnitudes as Helene
nears the Southern Appalachians to OH Valley region appeared too
low for the Thu to Sat. This is likely the result of the known low
bias of NBM deterministic wind magnitudes when stronger systems
work through an area. For those periods, the wind speed and wind
gust magnitudes were trended 25 to 50 percent toward the 90th
percentile magnitudes, especially for the higher terrain of 2000
feet and above. At this time, there appears to be a risk of wind
gusts of 40 mph or stronger across the Log Mountains, the
Flatwoods area of Pike County, and on Pine, Black, and Cumberland
Mountain as areas immediately downwind for Thu night into Fri.

Unsettled weather with chances for showers and storms at times
will linger with the upper level low west of the area to end the
weekend and to begin next week followed by this becoming an open
wave to end the period. A cold front should also approach to end
the period.

Diurnal ranges should be limited with the approach of Helene and a
lingering frontal zone across the area Thu to Fri with highs in
the low to mid 70s and lows in the low to mid 60s. Highs should be
near normal over the weekend before cooling a bit for Mon to Tue.

&&

.AVIATION...(For the 00Z TAFS through 00Z Wednesday evening)
ISSUED AT 819 PM EDT TUE SEP 24 2024

A nearing cold front led to showers and thunderstorms throughout
the afternoon and evening, some of these becoming strong with
large hail and damaging winds. As we head into the overnight, the
showers and thunderstorms will trend to more scattered in nature,
but may persist. However, the threat of anything become severe is
quickly diminishing. Models show coverage ramping back up during
the late night hours and into Wednesday morning. This may also
coincide with CIGs and VIS dropping into the MVFR category or
possibly worse. Expect VIS to lower further if there is a break in
the rain for a while and fog is allowed to develop. MVFR
conditions are forecast to persist through the rest of the
forecast period, as are the shower and thunderstorm chances. The
only thing that really won`t be impactful is the predominate
winds, with only light and variable forecast - although any
thunderstorm could result in some isolated wind gusts as it moves
through.

&&

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

$$

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