-- Discussion containing changed information from previous version are highlighted. --
524
FXUS63 KJKL 221903
AFDJKL

AREA FORECAST DISCUSSION
National Weather Service Jackson KY
303 PM EDT Sun Sep 22 2024

.KEY MESSAGES...

-- Changed Discussion --
- A potential for showers and thunderstorms will persist through
  much of this week.

- After high temperatures well into the 80s to near 90 today,
  readings will trend downward through the week.
-- End Changed Discussion --

&&

.SHORT TERM...
-- Changed Discussion --
(This evening through Monday night)
Issued at 302 PM EDT SUN SEP 22 2024

The frontal boundary that had been draped across far northern
Kentucky has begun to move north into Ohio and West Virginia as warm
advection increases across central and eastern Kentucky. Upstream
over the mid-Mississippi River Valley, a disturbance continues to
move east toward eastern Kentucky, and will be the primary trigger
for shower and thunderstorm development later this afternoon into
the early evening. The greatest instability will be over the
southwestern quadrant of the forecast area, but there will be
sufficient instability for thunderstorms anywhere across the
forecast area into this evening.

Additional rounds of showers and thunderstorms are possible into the
overnight tonight, with the greatest instability over the southern
half of the forecast area, as an active jet stream continues to
usher disturbances across Kentucky. With at least broken cloud cover
and continued warm advection, expect little in the way of any ridge-
valley temperature differences. Fog will be dependent on the amount
of cloud cover.

A stronger southwesterly jet stream develops over Kentucky Monday,
and this combined with stronger moisture advection into the area
will result in MLCAPE values approaching 1500-2000 J/kg by early
to mid-afternoon. The increasing shear and sufficient instability
will mean a Marginal Risk for severe thunderstorms, with gusty
winds and large hail the primary severe threats. A mitigating
factor may be that the better shear does not arrive until after
sunset, when instability becomes more limited, especially if
earlier convective overturning has resulted in stabilization of
the atmosphere. With the strong upper trough still approaching
from the west, showers and thunderstorms are likely to continue
through the overnight Monday night. Despite the recent dry
conditions, isolated/localized instances of high water are
possible where storms train across particular area.

.LONG TERM...(Monday night through Saturday)
Issued at 529 AM EDT Sun Sep 22 2024

While confidence is high that the first half of the long term
forecast period will be defined by wet and cloudy sensible weather,
model guidance continues to disagree on how the upper air pattern
will evolve in the second half. Because of this atypical amount of
uncertainty, it is important to note the overarching trends within
the forecast model ensembles rather than latching onto one
particular deterministic solution. In the most recent model runs, a
few of these trends have been observed, and their localized effects
have been outlined below.

The period opens with leftover convection from the daytime hours on
Monday. Given that limited levels of instability will mitigate the
severe weather risk earlier in the day, any remaining storms on
Monday night will weaken with the loss of daytime heating. However,
showers and perhaps some more thunderstorms remain in the forecast
for Eastern Kentucky through Wednesday. The first observable trend
in the latest model guidance has been the slower propagation of the
longwave troughing responsible for this disturbed weather. Ahead of
this troughing, modestly strong midlevel flow out of the southwest
will pump plenty of moisture into the atmospheric column.
Correspondingly cloudy skies will once again relegate diurnal
warming processes, and highs will struggle to climb above 80 degrees
on Tuesday afternoon. Despite the meager thermodynamics, sufficient
wind shear and better forcing/lift will foster the development of
more general thunderstorms on Tuesday. By Wednesday, most of the
activity looks to be in the form of low-impact, highly-beneficial
rain showers. The aforementioned longwave trough will have shifted
further east, allowing a cold front will push into the region.
High/low temperatures will accordingly decrease into the the mid
70s/lower 60s on Wednesday, and the air will become increasingly
stable as a result.

For Thursday and beyond, the focus shifts towards the Gulf of
Mexico, where the National Hurricane Center has diagnosed an area
with a 70% chance of tropical cyclone formation in the next 7 days.
Here in Eastern Kentucky, the sensible weather forecast for late
next week will depend on how this developing tropical system phases
with the upper level synoptic features. As discussed above, models
agree that some form of positively-titled troughing will exist in
the Mississippi River Valley by mid week. However, they do not agree
on the strength and exact positioning of this feature. The second
observable trend in the forecast guidance suite is that the European
ensemble of models collectively resolves this upper low further to
the southwest and stronger. Some Euro members depict a closed,
cutoff upper low over the Ozarks; this would signal a slower, less
progressive upper air pattern. On the other hand, the American
ensemble continues to show a weaker upper low over the mid-south and
thus a more progressive pattern. A stronger, western feature aloft
would pull the tropical system`s remnants further to the northwest,
which, in turn, could lead to downsloping and dry slotting over our
forecast area. If this particular trend becomes the consensus, the
extended forecast may need to be adjusted towards drier conditions,
but the chance PoPS from the NBM have been kept in the grids for
now. The third observable model trend is that both ensembles have
trended the system towards a faster forward motion and a further
northeast position on Friday morning. Both the speed and location of
this tropical cyclone will contribute to how it phases with the
previously-discussed upper level synoptic features, which, in turn,
will determine the sensible weather specifics. Given this recent
change, the uncertainty shrouding this system remains high, and we
will need these trends to continue in several more model runs before
drawing more definitive conclusions about localized impacts in the
Commonwealth. As such, we continue to encourage interested parties
to stay tuned to future forecast issuances.
-- End Changed Discussion --

&&

.AVIATION...(For the 18Z TAFS through 18Z Monday afternoon)
ISSUED AT 124 PM EDT SUN SEP 22 2024

Mainly VFR conditions are expected to last into tonight. However,
isolated thunderstorms are forecast to this afternoon and last
into the evening before dissipating. Additional scattered showers
and thunderstorms may occur overnight, but this is lower
confidence. Any thunderstorm or heavy shower has the potential to
bring sub-VFR conditions. Valley fog and low status are also
forecast once again tonight, but its extent is questionable. If
significant precip occurs first, it would favor fog. However, the
presence of clouds would also inhibit fog development. Additional
more widespread showers and thunderstorms are expected to develop
at the very end of the TAF period, which will be reflected in
future TAF packages.

&&

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

$$

SHORT TERM...CMC
LONG TERM...MARCUS
AVIATION...CMC