809
FXUS63 KJKL 260836
AFDJKL

AREA FORECAST DISCUSSION
National Weather Service Jackson KY
436 AM EDT Thu Sep 26 2024

.KEY MESSAGES...

- 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.

&&

.UPDATE...
Issued at 200 AM EDT THU SEP 26 2024

No significant changes to the forecast with just the inclusion of
the latest obs and trends for the T/Td/Sky/PoP grids - including
the current CAMs thoughts. These minor adjustments have been sent
to the NDFD and web servers along with a freshening of the zones,
HWO, and SAFs.

UPDATE Issued at 1130 PM EDT WED SEP 25 2024

Showers continue late this evening, largely along the US-23
corridor and eastward. A few showers are also lifting northward
into the Lake Cumberland area along the stalled frontal boundary.
Still anticipate a resurgence in shower coverage and intensity
from SSE to NNW between 6 and 9z as next surge of moisture/upper
level energy approaches.

UPDATE Issued at 800 PM EDT WED SEP 25 2024

No significant changes with this update. Refined overnight PoP
forecast to reflect latest hi-res solutions -- expect showers to
increase in coverage again, particularly after 6z. The soggiest
conditions will be found over the southeastern half of the CWA.

&&

.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 night through Wednesday)
Issued at 436 AM EDT THU SEP 26 2024

The remnants of Hurricane Helene is going to be the main story of
the forecast heading into the extended. By 0Z Saturday the upper
level low associated with Helene will have merged with the upper
level low already in place across western KY. This merged mega
system will remain nearly stationary during the first half of the
day Saturday, before slowly moving eastward to the eastern half of
the state Saturday night. The ECMWF is a bit slower with this
progression, however, keeping the center of the low across western
KY during this time. This sets the stage for model differences
moving forward, with the ECMWF always being about 12 to 24 hours
behind and displaced farther west than the GFS. This could lead to
considerable differences in weather patterns across the
Commonwealth, as one has the center of the low across the state
(ECMWF) while the other (GFS) has moved well east of the state
leaving us in NW flow. Furthermore, the GFS brings a shortwave
through the Ohio Valley on Tuesday night into Wednesday morning,
while the ECMWF starts to build ridging across the area. All this to
say, held to the NBM after Saturday for sensible weather as a best
guess between the two solutions.

The swath of heavy rain that impacted us Friday will start to wrap
north and eastward by Friday night, centering over western and
central KY, with most models showing some drying taking place in the
eastern CWA. This will persist through the first part of the day
Saturday, until the system starts to make the above-mentioned shift
eastward. Again, this is with the exception of the ECMWF which keeps
the precip across the western and central portion of the state
through the day Saturday and into Saturday night, keeping eastern KY
dry. The NBM seems to be more in line with the GFS and NAM,
spreading precip back into the eastern CWA by the second half of the
day Saturday. Either way, QPF will have tapered off substantially by
this point, with the best chances of totals around half an inch or
so generally across the Bluegrass. The NBM has rain chances
lessoning overnight with the loss of daytime heating/mixing, but
ramps it back up across the eastern half of the state during the day
Sunday. Interestingly, the same thing occurs on Monday, which seems
more in line with the solution of the slower ECWMF, and a bit higher
than the exiting GFS suggests. Will be interesting to see if these
pops trend lower or remain likely depending on which solution the
models continue to trend towards.

After this point, the NBM continues to trend drier, with Wednesday
likely being our first dry day in well over a week. Granted this
isn`t exactly reflected in the models currently, especially with the
GFS shortwave moving through, so expect that it could change as
models hopefully come into better agreement over the coming days.

One thing is for certain, the NW flow into the region through much
of the period. This will likely peak by mid-week as part of the
upper level jet dips down into the Commonwealth. As such, this
northerly flow and presence of clouds plus precip will help to keep
temperature at bay, with daytime highs generally in the low to mid
70s. By the end of the period, the clearing skies and lack of
rainfall will help temperature to drop further overnight. Therefore,
if the forecast holds, can`t rule out some temps in the upper 40s
and low 50s for Tuesday night, and then down into the mid 40s by
Wednesday night with another day of drying and clearing. The rest of
the time clouds should keep us fairly insulated, with temperatures
only bottoming out in the upper 50s and low 60s for lows.

&&

.AVIATION...(For the 06Z TAFS through 06Z Thursday night)
ISSUED AT 210 AM EDT THU SEP 26 2024

Variable aviation conditions were reported at TAF issuance time as
areas of fog, low clouds, and a few showers are impacting the
forecast area. Anticipate conditions to generally continue
worsening to mainly MVFR visibility but IFR CIGs into dawn. 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 in
showers, low clouds, and patchy fog. Winds will be light and
variable away from any storms.

&&

.JKL WATCHES/WARNINGS/ADVISORIES...
Flood Watch from 8 AM EDT this morning through Friday evening
for KYZ080-084>088-110-113-115>118-120.

High Wind Watch from this evening through Friday evening for
KYZ087-088-118.

&&

$$

UPDATE...GREIF
SHORT TERM...JP
LONG TERM...JMW
AVIATION...GEERTSON/GREIF