339
FXUS63 KJKL 180109
AFDJKL

AREA FORECAST DISCUSSION
National Weather Service Jackson KY
909 PM EDT Tue Sep 17 2024

.KEY MESSAGES...

- Shower chances taper off this evening.

- Additional shower (and possible thunderstorm) chances will occur
  through Thursday.

- A warming trend will lead to temperatures around 10 degrees
  above normal over the upcoming weekend.

&&

.UPDATE...
Issued at 909 PM EDT TUE SEP 17 2024

Precip has been on an overall decline this evening. The most
significant showers remaining are in our southwest counties. Have
updated the POP for this evening based on these trends, with
mainly a sub-20% POP to follow for the overnight, as models and
radar would suggest.

&&

.SHORT TERM...(This evening through Wednesday night)
Issued at 507 PM EDT TUE SEP 17 2024

Upper level low and associated surface wave will spin its way up
the northern half of the Piedmont during the short term, opening
up into a trough as it tracks towards New England. Short wave
energy rotating around the low will keep the threat of some type
of afternoon convection in place across portions eastern Kentucky
through the period. There is a band of showers, and further
upstream, thunderstorms lining up along the NC/VA state line that
is moving downstream into eastern Kentucky. SPC mesoanalysis shows
a lobe of MLCAPE nosing its way as far northwest as Wise, VA. But
otherwise, the better instability remains outside of our forecast
area. This line takes on an increased east to west orientation
with time. Consequently, this source of moisture into eastern
Kentucky will eventually get shunted off to the south of our area
by this evening.

Sensible weather features an unsettled short term, with the bonus
of the chance of receiving some much needed rain, even if
relatively meager in amounts. Being at an upslope location, Big
Black Mountain has come out on top with almost 1.5 inches of
rainfall today. Totals drop off quickly from there with around a
half inch directly down from Black Mountain, across the immediate
tier of counties from the VA state line. From there, the next tier
of counties going west- northwest had just under a quarter of an
inch of rainfall, with lesser amounts further to the west-
northwest, around a tenth or less of precipitation. Up to another
tenth of an inch on average will be possible through the short
term...where showers pass. Have not seen any thunder thus far and
expect that to remain the case in general through the remainder of
the late afternoon and evening. However, with MLCAPES of 750-1000
J/kg, there is slightly better instability to work with on
Wednesday.

.LONG TERM...(Thursday through Tuesday)
Issued at 438 PM EDT TUE SEP 17 2024

The 17/12z model suite 500H analysis beginning Thursday morning
shows a lingering trough from southern New England SSW into the
Carolinas. Meanwhile, a narrow but robust, positively-tilted
ridge extends from an ~591 dam high over Coahuila, Mexico NE over
the Mid-Mississippi Valley and Western Great Lakes and then N
across the Hudson Bay. West of the ridge, there is a mean trough
with embedded closed lows over southern Saskatchewan/Manitoba and
also along the Central California coast. At the surface, a subtle
trough lingers along the western slopes of the Central
Appalachians amidst a larger area of high pressure extending into
the Ohio Valley from out of eastern Canada. A potent ~990 mb low
is found under the first upstream low over southcentral Canada and
is attended by a wavy cold front that extends down the High
Plains all the way into Mexico.

The 500H troughing to our east slowly departs on Thursday/
Thursday night and any surface disturbance dissipates, ending the
threat for any lingering PoPs. Ridging subsequently becomes more
positively tilted across Ohio Valley by Friday as the first 500H
low and its surface reflection become vertically stacked and decay
over Central Canada while the associated cold front slows out
over the Upper Midwest and stalls. Ahead of that boundary, an
increasingly mild west to southwesterly flow sends 850mb
temperatures back into the 17-19C range across eastern Kentucky
for Saturday and Sunday, setting the stage for well above normal
temperatures. Meanwhile, the second 500H low passes over the Four
Corners on Saturday and ejects out onto the Central Plains Sunday.
This next upper low fosters renewed cyclogenesis in the
baroclinic zone of the remnant cold front near/over eastern
Colorado on Saturday night. This new surface low tracks northeast
to near Chicago, IL by late Monday/early Tuesday, dragging the
trailing cold front to over the Lower Ohio Valley. By this point
in the forecast period, there are substantial model-to-model
differences in the intensity and timing of the front. Given the
uncertainty, the NBM was left unchanged, aside from some very
minor adjustments to account for topography.

In sensible terms, a lingering small chance (15-30 PoP) for showers
and thunderstorms will still be possible east of a Paintsville-to-
Jackson-to-Barbourville line. Otherwise, mostly sunny skies are
expected to accompany maximum temperatures in the lower to middle
80s. Fair skies follow for Friday and the weekend with temperatures
reaching the mid 80s for most locations on Friday and then mid to
upper 80s on both weekend days. A few thermometer readings near
90F cannot be ruled out on either Saturday or Sunday. Nighttime lows
range from the mid 50s to mid 60s through the weekend. Normal
daily high temperatures for September 21st and 22nd are in the
mid 70s to near 80 and lows range in the 50s. Heading into the
new work week, forecaster confidence is low due to model spread.
NBM-based forecast favors increased cloud cover, slight rain
chances, and closer to normal temperatures returning the forecast
on Monday and Tuesday as the next cold front approaches.

&&

.AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon)
ISSUED AT 158 PM EDT TUE SEP 17 2024

Shower activity continues across the area this afternoon, though
there is a gradual decrease in activity. CIGS have been hovering
in MVFR territory, with brief rises into VFR flight conditions
where some thinning of clouds/breaks in shower activity have
occurred. Lower stratus will develop and build down overnight,
bringing CIGS down into IFR territory for a period of time through
the early morning and pre-dawn hours Wednesday. Light fog will
also lower VSBYS. These lower flight conditions will be slow to
improve late in the forecast period, but are expected to rise into
VFR conditions by around 14-15Z. Winds will be light, around 5
kts or less with an east-southeast tendency.

&&

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

$$

UPDATE...HAL
SHORT TERM...RAY
LONG TERM...GEERTSON
AVIATION...RAY