112
FXUS63 KJKL 252350
AFDJKL

AREA FORECAST DISCUSSION
National Weather Service Jackson KY
750 PM EDT Wed Sep 25 2024

.KEY MESSAGES...

- Showers and a few thunderstorms could result in heavy rain and
  isolated flooding through tonight.

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

- Flash flooding could result from the remnants of Helene, but the
  potential may be limited by its quick movement.

- Wind gusts of 40 to 60 mph are possible at times from Thu night
  to Fri as the remnants of Helene pass to the southwest.

&&

.SHORT TERM...(This evening through Thursday night)
Issued at 500 PM EDT WED SEP 25 2024

Late this afternoon, an upper level ridge extended from the
western Atlantic northwest to the west of Bermuda toward the
Canadian Maritimes while another upper level ridge centered over
the Southern ROckies to northern Mexico area and extended to the
northern Plains to central portions of Canada. An upper level low
and trough were moving through the Hudson Bay to Ontario to
Central Great Lakes area, while the southern end of this trough
has closed off to an upper level low over the past 24 hours and
was centered in the Lower OH Valley region. Meanwhile, Hurricane Helene
continues to organize/strengthen in the eastern Gulf of Mexico to
the west of Cuba. At the surface, an area of low pressure was
centered north of the Great Lakes with a frontal zone extending
into the Commonwealth to TN Valley to the Lower MS Valley to
southern TX. Multiple weaker shortwaves moving around the upper
level low are interacting with the boundary and lingering
moisture with PW of 1.3 to 1.6 inches across the region. The
highest PW and highest 100 mb mean mixing ratios are located
across the Big Sandy region to northeast TN to the the Gulf coast
states. Convection today has been most persistent across the Big
Sandy region to the VA border.

This evening and tonight, an initial shortwave trough associated
with the ongoing convection will lift north early this evening,
but another shortwave or two will move in quickly behind it later
in the evening and during the overnight. These will rotate across
the area as the upper level low meanders to near the confluence of
the OH and MS Rivers. These will interact with moisture remaining
across the region, PW generally 1.4 to 1.6 inches, and the
boundary and result in continued rounds of convection during the
evening and into tonight. At the same time, Helene will continue
to the north and likely become a major hurricane.

Thursday to Thursday night, the upper level low is expected to
drop south to south of Memphis TN as upper level ridging builds
north of the western Atlantic and a shortwave upper level ridge
builds into the Great Lakes and the upper level ridge in the
western Conus/Rockies retrogrades west. Helene should be drawn
into the Souther Appalachian region as this occurs with the
pressure gradient and winds aloft increasing as it does so on
Thursday night. Precursor rainfall associated with the upper
level low to the west and shortwaves rotating around it
interacting with the boundary nearly stalled out near or just west
of the area will lead to continued rounds of convection into
Thursday, especially across the south and southwest portions of
the area. Helene should begin to merge and interact with the
boundary by the end of the period. PW should initially be 1.4 to
1.6 inches per 12Z HREF and then climb to 1.7 to 1.8 inches on
Thursday afternoon. Further increases in PW to 1.9 to 2.1 inches
should occur on Thursday night. More of a stratiform rainfall
should develop and move into the are on Thursday night as Helene
works into the southern Appalachians. This could be heavy in a few
locations, but QPF has generally trended down for Thursday night
with a track a bit more west/southwest of eastern KY. The
increasing gradient should result in an increase in wind speeds
and gusts in the more open terrain and locations above 2000 feet
near the VA border on Thursday night. A High Wind Watch has been
hoisted for Bell, Harlan, and Letcher counties starting at 11 PM
on Thursday night and this runs into Friday. Some guidance
suggests a possible increase in wind gusts to at least wind
advisory criteria from US 25E to near London north along I-75 and
points west late on Thursday night. The strongest wind gusts for
most locations may hold off until Friday however.

.LONG TERM...(Friday through Wednesday)
Issued at 352 PM EDT WED SEP 25 2024

The forecast period begins with the area beginning to feel the
impacts from the remnants of Helene. The hurricane is expected to
make landfall on the Florida Panhandle Thursday evening and through
the overnight hours quickly track north-northwestward toward the
Commonwealth. By the start of the extended forecast window, the NHC
has Tropical Storm Helene moving up the spine of the Appalachian
Mountains but getting sheared apart by frictional forces from the
mountains. The bulk of the remnants are expected to take a hard
westerly turn to the northwest and fizzle out and get absorbed into
a cut-off upper-level closed circulation. However, before that
occurs, wind and rain will pound the entire CWA starting Thursday
night and persisting through Saturday morning. Total QPF through the
duration of Helene is expected to range from 1.00" to 1.50" along
the eastern mountains to upwards of almost 2.00" to 3.00" along and
west of the I-75 corridor. The easterly flow across the southeastern
mountains will create a rain shadow effect for counties along the
mountains and diminish overall QPF; however, the further away from
the mountains; the less impact rain shadowing has on the QPF. Near
high wind warning criteria winds are expected across the high
terrain of the eastern mountains with sustained winds approaching 20
mph in the lower elevations are expected through Friday evening.
Higher upper-level winds exist; however, with no widespread
convection or mechanism to translate those winds to the surface,
those winds will remain aloft. Through the evening Friday into
Saturday, Helene will drift west-northwest toward western Kentucky
and eventually be absorbed into a closed circulation that`s been
largely stationary all week.

After the merging of the closed circulation and the remnants of
Helene takes place, the closed circulation will continue to
aimlessly spin over the Commonwealth and keep persistent chances of
showers and thunderstorms through the weekend. Models continue to
remain in rather good agreement going into next week with the
circulation getting picked up by the mean flow and ejecting out of
the area by Monday morning but lingering PoP chances will exist
through the end of the period as an upper-level trough, moving
through southern Canada, drags a cold front through the region
Tuesday afternoon which will then usher in cooler and drier weather
for the middle of next week.

Overall, the forecast period will be highlighted by multiple rounds
showers and thunderstorms. The remnants of Helene will bring the
best chances through Friday afternoon before the closed circulation
keeps PoP through the middle of next week. Temperatures through the
period will remain rather seasonal as highs are forecast to in the
upper-60s to upper-70s. Overnight lows, will be warmer with the
approach of Helene but with the approach of a cold front on Tuesday,
cooler temperatures and fall-like weather will be in place for the
end of the period.

&&

.AVIATION...(For the 00Z TAFS through 00Z Thursday evening)
ISSUED AT 750 PM EDT WED SEP 25 2024

VFR conditions were reported at TAF issuance time. Anticipate
conditions worsening to mainly MVFR from southeast to northwest
overnight as the next round of showers move through the area. A
rumble of thunder cannot be ruled out, but confidence in
occurrence at a particular TAF site was too low to mention. MVFR
or worse conditions can be expected during the day on Thursday.
Winds will be light and variable.

&&

.JKL WATCHES/WARNINGS/ADVISORIES...
High Wind Watch from Thursday evening through Friday evening for
KYZ087-088-118.

&&

$$

SHORT TERM...JP
LONG TERM...VORST
AVIATION...GEERTSON