JKL issues Area Forecast Discussion (AFD) at Sep 17, 2:45 PM EDT
358
FXUS63 KJKL 171845
AFDJKL
AREA FORECAST DISCUSSION
National Weather Service Jackson KY
245 PM EDT Thu Sep 17 2026
.KEY MESSAGES...
- Well-above normal temperatures persist into the weekend, with
near- record heat this afternoon.
- The heat and humidity could fuel isolated thunderstorms across
the area at various times over the next several days.
- Rain chances increase early next week as the persistent upper
level ridge starts to weaken and then retreat to the southwest.
&&
.SHORT TERM...(This evening through Friday night)
Issued at 244 PM EDT THU SEP 17 2026
Weak north to northwesterly upper flow can be expected as the
area resides on the northeast side of a strong high that will be
centered over the Arklatex region. Meanwhile, at the surface, a
cold front will move south into the area Friday morning but then
quickly decay/dissipate as any upper support for southward
movement falls apart.
Hot and humid conditions will provide the fuel for isolated to
scattered shower and thunderstorm development both for the remainder
of this afternoon, and then again Friday morning through Friday
evening with more widespread scattered coverage. Lift will be
provided by subtle shortwave disturbances inducing upstream
convection focused near/along the cold front, with additional shower
and thunderstorm activity forming along differential heating
boundaries and localized terrain effects Friday afternoon before
largely dissipating Friday evening.
The arrival of the cold front and potential convection from the
north Friday may provide some relief from the scorching conditions,
though the trend has been upwards with forecast temperatures in the
last 24 hours across the north. South of the Mountain Parkway,
however, it will be another hot day with temperatures reaching the
lower to mid 90s for highs, with heat indices reaching 100 degrees
or slightly higher in the greater Lake Cumberland area.
The typical valley fog can be expected tonight, and may be locally
dense where rain occurs this afternoon and/or evening, with fairly
low ridge-valley splits of no more than 3 to 6 degrees in the deeper
valleys. More widespread fog is possible Friday night behind
scattered shower and thunderstorm activity along with very weak cold
advection in the wake of the dissipating cold front.
.LONG TERM...(Friday night through Wednesday)
Issued at 400 AM EDT THU SEP 17 2026
The extended portion of the forecast looks to still be on track
with the idea of the large 5h ridge weakening further, drifting
southwest and out of the region enough through the weekend for
more intrusions of energy at mid levels. This should keep mainly
unorganized convection as part of the forecast into the new work
week even as we remain unseasonable warm.
The previous long term discussion follows:
A pattern change is in store for Eastern Kentucky during the long
term forecast period, and it should bring some relief from the
recent heat with it. The previously-dominant ridging over the
Tennessee Valley is progged to retrograde west towards the Ozarks
this weekend. At the same time, a closed upper level low will move
over the Floridian Peninsula and set up a Rex-esque blocking feature
for a few days. Models collectively resolve both of these features
sitting in place through Sunday morning, although the ridging will
be in a weakening state. A series of troughing disturbances ejecting
around the ridge's northern periphery will work in tandem with this
closed low to suppress the ridge by early next week. While the
initial two disturbances will yield minor sensible weather impacts
across the forecast area, a deeper trough is expected to eject out
of the Rockies early next week. While models disagree on its exact
evolution, they do agree that it will be the final nail in the
coffin for the antecedent ridging pattern. Between Friday morning
and Monday afternoon, the ridge is poised to weaken from its peak
"heat dome" intensity of 600+ decameters to a looser-organized ridge
of sub-590 decameter heights. Therefore, this late-period troughing
disturbance is more likely to bring noticeable heat relief to all of
Eastern Kentucky than its predecessors.
The first disturbance is expected to pass well to the north of the
Ohio River Valley on Friday, with weak northwesterly flow and
minuscule midlevel height falls modeled across the forecast area.
While a surface frontal boundary is resolved in the vicinity of the
forecast area in this time frame, there will be little to no
syntopic-scale airmass modification associated with it. Temperatures
in the northeastern half of the CWA will be a few degrees cooler
than they were in the short term forecast period, but this moreso a
byproduct of the cloud cover from the convective activity associated
with the boundary. Given the lack of dynamic support aloft, any
showers/storms on Friday will be well below severe limits. The lack
of forcing should also limit the heavy rainfall potential. So, the
greatest sensible weather effects from this activity will come in
the form of a SW->NE temperature gradient. There could be a 10
degree difference in highs on Friday between NE KY and areas west of
I-75 that are closer to the influence of the ridge. The latest data
blend accordingly depicts highs in the mid 80s in the Big
Sandy/Licking River Basin, whereas places closer to the Cumberland
River will experience yet another day of temperatures in the 90s.
Any rain that does fall on Friday could help bolster the areal
coverage of fog on Friday night, when temperatures should cool into
the 60s area wide.
Given the blocking to the south and the quasi-zonal flow aloft, the
boundary responsible for Friday's activity is expected to hang
around into Saturday. Models resolve low-level flow adopting more of
a southerly directional component on Saturday and Sunday, this is
associated with the boundary nudging back north of the Ohio River in
this time frame. The resultant warm air advection will bump
temperatures back into the upper 80s/lower 90s area-wide on both
days. Isolated summertime showers/storms cannot be ruled out during
peak diurnal heating hours on Saturday, but there could be greater
convective coverage late Saturday night into Sunday. The second
ridge-riding impulse is expected to arrive in the latter stages of
the weekend, with relatively greater shortwave support aloft than
Friday's. WPC has outlined a Marginal Excessive Rainfall outlook in
the vicinity of the forecast area for late Saturday night and then
again on Sunday, but this appears contingent on the evolution of
upstream activity on Saturday night. A few isolated hydro impacts
cannot be ruled out where multiple rounds of activity occur in the
vicinity of the increasingly stationary boundary, but this is
most likely to be north and northeast of the JKL CWA.
There is a notable increase in model spread within the NBM ensemble
across multiple sensible weather forecast parameters for Sunday and
beyond. This is likely due to differing model solutions
surrounding the third trough ejecting out of the Rockies.
Significant variations in this feature's modeled amplitude,
orientation, phasing, and forward progression speed preclude the
discussion of specific forecast details at the present moment, but
models generally agree that a deeper, vertically-stacked trough will
move through the Midwest and the Greater Ohio River Valley by
midweek. It would take a trough like this to finally drag a
meaningful cold front through the CWA, and despite the model spread,
there is a noticeable downward trend in the mean forecast MaxTs and
MinTs for Tuesday and Wednesday. Highs dip down into the low/mid 80s
by Wednesday alongside widespread lows in the 60s (not accounting
for smaller-scale enhanced radiational cooling in the valleys). Such
values are technically still above climatological norms for Mid-
September in Eastern Kentucky, but we will cling onto the glimmer of
hope that is some type of relief from this week's near-record
heat.
&&
.AVIATION...(For the 18Z TAFS through 18Z Friday afternoon)
ISSUED AT 124 PM EDT THU SEP 17 2026
VFR conditions will prevail through much of the TAF period.
Later this afternoon, showers and thunderstorms will be possible
again - mainly east of I-75. Thunder probabilities were sub-30%
for all sites except KSJS; therefore, a PROB30 was included there
from 19z to 23z.
Additional PROB30 groups were added beginning around 12z Friday at
KIOB and KSYM, where models are coming into better agreement on
decaying showers from earlier thunderstorm activity moving south
or southeast into the eastern Kentucky. These have the potential
to bring reductions to MVFR or lower if these occur. Better
chances for showers and thunderstorms across much of the areas
will begin to develop at the very end of the TAF period.
Valley fog will develop again tonight, and may locally dense
where rain occurs late this afternoon into early evening. These
are not likely to impact TAF sites. Winds away from any storms
will be light and variable today into tonight, then trend from the
north beginning at less than 10 kts after 15z Friday.
&&
.JKL WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
SHORT TERM...CMC
LONG TERM...MARCUS/GREIF
AVIATION...CMC
Source: JKL issues Area Forecast Discussion (AFD) at Sep 17, 2:45 PM EDT (https://mesonet.agron.iastate.edu/p.php?pid=202609171845-KJKL-FXUS63-AFDJKL)
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