855
FXUS63 KJKL 160335
AFDJKL

AREA FORECAST DISCUSSION
National Weather Service Jackson KY
1135 PM EDT Tue Sep 15 2026

.KEY MESSAGES...

- Above normal temperatures will persist into the weekend, with
  near record heat possible on Thursday.

- The heat and humidity could fuel a few thunderstorms in portions
  of the area at times over the next several days, with the
  probability then rising early next week as upper level high
  pressure currently dominating the area weakens.

&&

.UPDATE...
Issued at 1135 PM EDT TUE SEP 15 2026

The first signs of valley fog are materializing on satellite
imagery in southeast KY, and it will continue to develop through
sunrise. The forecast is on track, and no substantive changes were
necessary.

UPDATE Issued at 714 PM EDT TUE SEP 15 2026

Diurnal cu is drying up, and sky cover going into tonight has
been reduced. Based on dew points during peak mixing in the
afternoon, have raised fcst min temperatures slightly in valleys
for sunrise on Wed. Also, extended a 20% POP into early Wed night
in our northern counties based on latest mesoscale model runs.

&&

.SHORT TERM...(This evening through Wednesday night)
Issued at 357 PM EDT Tue Sep 15 2026

Forecast confidence remains high that the sensible weather in
Eastern Kentucky will be governed by an anomalously strong ridge
for the next couple of days. The guidance suite collectively
resolves a potent mid/upper level ridge over the Tennessee and Ohio
River Valleys today. That ridge is progged to amplify over the next
24 hours, peaking with a closed 600 decameter contour just to the
southwest of the forecast area tomorrow evening. 500mb geopotential
heights of this magnitude rank at the 100th percentile of model
climatology within the HREF ensemble data, and that signal has been
consistent across many successive model runs. Given the proximity of
this intense mid/upper level ridging, today and tomorrow`s sensible
weather forecast will largely be driven by the subsidence, dry air,
and clockwise wind pattern associated with this ridging and surface
anticyclone.

This afternoon`s surface analysis resolves that anticyclone over the
Southern Appalachians. Breezy west-southwesterly low-level flow
around its northwestern periphery has advected just enough moisture
into the column for a field of cumulus clouds to blossom in Southern
Kentucky today. These clouds are met with a hostile environment
aloft though. Synoptic subsidence is limiting their vertical
growth/depth and the antecedently dry airmass is limiting both their
northward extent and ability to produce precipitation. The entire
area should accordingly experience dry and unseasonably warm weather
through this evening. The forecast for widespread highs in the upper
80s (NE KY), lower 90s (KY-15 corridor), and mid 90s (west of I-75)
remains on track, and while these values are above climatological
averages for Mid-September, we are not near heat advisory criteria.
Efficient diurnal mixing will allow dewpoints to mix out into the
60s in the more populated valley locales, which should keep heat
indices below the 100 degree mark in most places. A few isolated
readings around 100 degrees proper cannot be ruled out in our
westernmost counties though.

Once the sun begins to set and diurnal heating/mixing processes
subside, those diurnal cumulus clouds will give way to mostly clear
skies. Expect efficient radiational cooling once this happens, and
ridge-valley splits have been retained in the forecast grids as a
result. While warmer ridgetop locales will experience lows closer to
the 70 degree mark, the valleys will quickly drop down into the 60s.
A few isolated readings in the upper 50s cannot be entirely ruled
out in the coldest hollows. As cold air pools in the valleys, fog is
expected to develop overnight. So, expect areas of fog to produce
sporadic visibility reductions during tomorrow morning`s commute
along Eastern Kentucky`s highways, especially when those highways
parallel a waterway.

Persistence forecasting prevails into Wednesday, when the ridge will
reach its aforementioned maximum magnitude. However, a subtle
southwestern shift in the ridge`s positioning will yield a
relatively deeper regime of moisture return across the CWA. A
modified plume of Gulf moisture is expected to wrap around the
western and northern periphery of the ridge tonight before settling
across the Upper Ohio River Valley tomorrow. The deepest moisture is
expected to remain to the north of the JKL CWA, but there is enough
of a model signal to introduce slight chance PoPs to tomorrow`s
afternoons forecast grids. Isolated showers and perhaps a
thunderstorm cannot be ruled out in locations north of the Mountain
Parkway corridor. Any activity that does occur is unlikely to yield
any hazardous weather impacts given the hostile conditions presented
by the strong ridging aloft. There is very little forcing or shear
for organized thunderstorms in Eastern Kentucky tomorrow, and the
primary lifting mechanism would be reaching convective temperatures
in the 90s. With widespread forecast highs in the 90s, that does
appear plausible. Expect another day with widespread heat indices in
the mid/upper 90s, but we will likely remain below heat advisory
criteria (105 degrees) yet again. Once any diurnal convection dies
down tomorrow evening, ridge-valley low temperature splits and river
valley fog re-enter the forecast for Wednesday night into Thursday
morning.

.LONG TERM...(Thursday through Tuesday)
Issued at 228 PM EDT TUE SEP 15 2026

High pressure and associated ridge axis aloft over eastern Kentucky
will retrograde and weaken with time, allowing for increasingly
faster west-northwesterly flow aloft through the Ohio Valley as the
long-term period progresses through the weekend.

Warm and mostly dry conditions are expected Thursday as strong mid-
level heights exceeding 597 dm gradually decrease, though low
chances for showers and thunderstorms are warranted across parts
of mainly central and northeastern Kentucky and perhaps extending
south to near the Cumberland Mountains in the afternoon. Highs are
expected to reach the upper 80s to lower 90s across the area, with
max heat indices in the vicinity of 100 degrees.

A passing disturbance to the north and associated jet streak will
push a cold front far enough south Friday to bring increased shower
and thunderstorm chances across the area along with a brief
modest cooldown in the northern half of the forecast area, but
highs will still reach the mid 80s to lower 90s.

Warm advection quickly returns for Saturday, with low PoPs and a
return to highs back into the upper 80s to lower 90s, which looks to
extend through Sunday before a potential cooldown as an upper
trough and associated cold front move into the area and increase
rain chances. While models show broad 40-50 PoPs Monday into
Monday night with relatively good agreement in a system moving
from the central CONUS to the Great Lakes region, model ensemble
systems show significant disagreements on the strength, track, and
timing of the parent trough. Resolving these differences will
likely play a key role in whether those PoPs trend upwards or
downwards as this period nears.

&&

.AVIATION...(For the 00Z TAFS through 00Z Wednesday evening)
ISSUED AT 833 PM EDT TUE SEP 15 2026

Mainly VFR conditions are forecast through the period, with only a
couple of exceptions. Valley fog will affect some locations,
especially southeast KY, late tonight and early Wednesday morning.
It will bring localized IFR or worse conditions, but should not
affect TAF sites. A few thunderstorms may occur near and north of
the Mountain Parkway late Wednesday into Wednesday evening,
bringing isolated sub-VFR conditions.

&&

.JKL WATCHES/WARNINGS/ADVISORIES...
None.

&&

$$

UPDATE...HAL
SHORT TERM...MARCUS
LONG TERM...CMC
AVIATION...HAL