165
FXUS63 KJKL 210933
AFDJKL

AREA FORECAST DISCUSSION
National Weather Service Jackson KY
533 AM EDT Sat Sep 21 2024

.KEY MESSAGES...

- A potential for showers and thunderstorms returns today and then
  persists for much of next week.

- High temperatures will approach 90 degrees through the weekend,
  then trend lower as time goes by during the week.

&&

.SHORT TERM...(Today through Sunday)
Issued at 442 AM EDT SAT SEP 21 2024

A weak cold front runs from northwest OH through southern IL early
this morning. Beneath meager west northwest flow aloft, it is
running out of momentum and is only expected to get as far as the
Ohio river or slightly into KY before it stalls. Weak moisture
advection ahead of the front will bring modest instability
today-- elevated at first, but becoming surface based with daytime
heating. Despite little support aloft, the front and the
instability could be enough to bring scattered showers and
thunderstorms. Any activity should die out this evening.
Depending on the progress of the front, drier air may try to nudge
into our area from the north tonight and early Sunday.

An upper low currently over AZ will move east northeast and meet
with a northern stream upper trough progressing eastward across
the north central CONUS on Sunday. This will strengthen our flow
aloft and support another cold front which will approach from the
Midwest. What`s left of the first frontal boundary lifts to the
northeast as a warm front ahead of the next cold front. This could
bring us a few showers or storms, especially late in the day
Sunday.

.LONG TERM...(Sunday night through Friday)
Issued at 531 AM EDT Sat Sep 21 2024

Long term forecast guidance continues to exhibit signs of a more
active weather pattern for the first full week of fall. On Sunday
night, after the equinox, Eastern Kentucky will be positioned in
between upper level ridging over the Appalachians and upper level
troughing over Greater Kansas City. A weak shortwave trough will be
pass through the Ohio River Valley overnight into Monday morning,
with a correspondingly weak surface frontal boundary nestled within
it. The passage of this first feature will increase shower and
thunderstorm chances, and as the aforementioned longwave features
shift east, this upward trend continues. Said shift will position
the region in strengthening southwesterly flow, leading to increased
moisture return. Given the antecedent warm air, general
thunderstorms appear likely across the region on Monday and Tuesday,
especially during the afternoon and evening hours. Concerns for
widespread, organized severe weather are not particularly high at
the moment, although the strength of the flow aloft and the
proximity of a surface low to the northwest may foster marginally
supportive wind shear. Increasing cloud coverage will work to
relegate instability, and probabilistic ensemble guidance only
depicts a 30-40% chance of greater than 750 J/kg of surface CAPE in
our CWA. An advection-driven, marginally more favorable
thermodynamic environment might emerge further to the west/closer to
the frontal boundary on Monday afternoon, so mesoscale trends will
need to be monitored closely in the coming days. For now, expect a
rather damp day, with highs in the low 80s, rain chances >50%, and
mostly cloudy skies. Unsettled weather will continue into Tuesday as
the front lingers nearby, but continuing cloud coverage will
contribute to slightly cooler afternoon highs near 80 degrees.
Thunderstorms are possible once again on Tuesday given increasing
frontal lift, but marginal thermodynamics will limit severe weather
chances once again.

Beyond Tuesday, the available forecast guidance diverges towards two
distinct groups of solutions. The first (including the ECMWF)
depicts a more progressive pattern in which the troughing aloft
lingers on Wednesday but slides east by Thursday evening. This would
keep rain showers in the forecast for Wednesday, but allow cooler
and drier air to filter in via northwesterly flow on the backside of
the trough by Thursday. Thus, seasonably appropriate temperatures
and a drying trend would emerge by next weekend.

The second set of solutions (including the GFS) would keep active
weather around for much longer. Rather than progressing the upper
level trough aloft, this solution phases it with an upstream
disturbance in Canada. This causes it to evolve into a closed upper
level low that stalls out over the Ohio River Valley. If this
materializes, rain chances and enhanced cloud coverage would
continue through the end of the forecast period.

To complicate things even further, a tropical cyclone appears likely
to develop in the Gulf of Mexico. The National Hurricane Center
currently gives this system a 60% chance of formation within the
next 7 days, and its forward progression will be determined by
whichever of the two upper level patterns comes to fruition. The GFS
solution is quicker and more aggressive; its closed low would pull
the system further north towards our area. The Euro solution
develops the cyclone more slowly, and any eventual impacts from it
would fall outside of the current forecast period. The latest
WPC/NHC guidance trends towards the slower of the two solutions.
Therefore, this forecast package generally reflects the first set of
solutions, although the greater than average level of uncertainty is
noted.

The grids in this particular long term forecast issuance generally
depict a drying and cooling trend after Wednesday, but keep broad-
brushed slight chance PoPs in through the end of the extended period
to account for these uncertainties. Expect highs in the 70s on
Wednesday, Thursday, and Friday, with overnight lows in the 50s. It
is important to note that this forecast can and will change as the
latest model data comes in. Interested parties are thus encouraged
to pay close attention to future forecast issuances, which will
reflect the latest model trends and detail any potential for
localized tropical impacts.

&&

.AVIATION...(For the 06Z TAFS through 06Z Saturday night)
ISSUED AT 341 AM EDT SAT SEP 21 2024

Satellite imagery and obs indicated fog developing in the deeper
valleys at the start of the period. It will continue to grow in
depth and breadth until sunrise, bringing localized IFR or worse
conditions. It is unlikely to affect TAF sites. Fog will dissipate
after sunrise.

Isolated to scattered showers and thunderstorms are forecast to
occur during the day, possibly by sunrise in our northern
counties. They will bring localized sub-VFR conditions. Otherwise
VFR conditions (post fog) should last into tonight before valley
fog again develops.

&&

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

$$

SHORT TERM...HAL
LONG TERM...MARCUS
AVIATION...HAL