773
FXUS63 KLMK 251047
AFDLMK

Area Forecast Discussion
National Weather Service Louisville KY
647 AM EDT Wed Sep 25 2024

...Updated Aviation Discussion...

.KEY MESSAGES...

*  Scattered showers and storms linger today and tonight, mainly
   across southern and eastern KY. No severe weather expected.

*  Widespread moderate to heavy rain and windy conditions on Friday
   as the remnants of Tropical Storm Helene move through the Lower
   Ohio Valley.

&&

.SHORT TERM /THROUGH TONIGHT/...
Issued at 334 AM EDT Wed Sep 25 2024

Some convective activity going on across the Bluegrass region at
this hour as scattered convection has re-fired thanks to some
lingering instability and a upper impulse positioned east of the
upper trough axis. In addition, we`re seeing mix of low stratus and
some fog across the area. Any fog concerns should be transient in
nature given the increasing upper sky cover, however could have some
patches of dense fog from now until an hour or two after sunrise.
Will continue to monitor.

A shortwave trough has closed off over the lower Missouri/Mid
Mississippi River Valley early this morning. This closed upper low
will meander just to our west today, before retrograding back to the
SW just a bit by tonight. Meanwhile, the upper jet to the east of
closed low will remain oriented SW to NE up the Appalachian spine,
roughly parallel to the surface frontal boundary. This setup should
keep the focus of most of our shower and storm chances across our
southern and eastern portions of the CWA today and tonight. Overall,
not as much instability to work with, and deep layer shear will be
weaker compared to yesterday. So, severe weather is not anticipated.
A few spots could pick up a quarter to half an inch of additional
rainfall through tonight for areas along and east of a Bowling Green
to Lexington KY line. NW of that line, amounts are more likely to
stay at a tenth of an inch or less.

Fairly small diurnal range expected for today as we sit under pretty
heavy cloud cover. Highs are only expected to reach into the mid and
upper 70s, with lows later tonight dropping mostly into the mid 60s.
Some mid to upper 50s possible west of I-65 where some clearer skies
are possible.

&&

.LONG TERM /THURSDAY THROUGH TUESDAY/...
Issued at 334 AM EDT Wed Sep 25 2024

All eyes are on Tropical Storm Helene for the medium-range portion
of the forecast. NHC still expects Helene to intensify rapidly over
the next 48 hours while moving generally NNE over the eastern Gulf
of Mexico. Unfortunately, Helene is forecast to strengthen into a
major hurricane by its landfall Thursday evening along the FL Big
Bend coast.

Locally, there is a chance for mainly scattered light rain on
Thursday. We really won`t feel any impacts from the tropical system
until late Thursday night and Friday. We`ll see steady moisture
advection as southeasterly low to mid-level winds begin to increase
slightly. The upper low to our west is forecast to wobble southwest
over SE Missouri and NE Arkansas. Light rain accumulations
(generally less than 0.10") will be possible south of I-64, with
perhaps a few spots in south-central KY seeing up to 0.10-0.20
inches. Cloud cover should be increasing quickly from east to west
by Thursday morning. Afternoon highs will range from the lower 70s
in the Bluegrass/Lake Cumberland regions to the mid/upper 70s west
of I-65.

Helene will gradually weaken after making landfall, but will race
northward fairly quickly through GA Thursday night. Widespread
moderate to heavy rainfall chances ramp up from south to north
overnight into Friday. Northeasterly sfc winds are forecast to
strengthen to around 15 kts prior to sunrise Friday. Overnight lows
in the low to mid 60s should be common.

Helene is forecast to then curve northwest over the Lower Ohio
Valley on Friday while wrapping cyclonically around the
southeastward rotating upper low (Fujiwhara effect). Widespread
tropical rains and windy conditions are likely. Gusts of 30-35+ mph
appear likely based on LREF data, but higher gusts are not out of
the question. The severe convective risk appears to be low at this
time, but confidence is low on the details until the forecast track
can be further refined. Minor flooding issues will likely become
more common on Friday with the arrival of tropical moisture after
multiple days of unsettled/convective weather.

Showery weather continues over the weekend. Post-tropical Helene
merges with the remnant upper low, and the wave spins over the Lower
Ohio Valley for a couple days before opening up and exiting off to
the northeast early next week.

Overall, 2-4+ inches of additional rainfall will be possible today
through Sunday. The highest amounts are likely to occur across
southern KY. This rainfall will significantly help alleviate drought
conditions across the region. While higher rainfall totals and a
higher flooding risk will exist across the Southeast, there may be
slight risk for isolated flash flooding Friday. Long-fused
significant river flooding is unlikely, as area rivers should be
able to handle this rainfall.

&&

.AVIATION /12Z TAFS THROUGH 18Z THURSDAY/...
Issued at 646 AM EDT Wed Sep 25 2024

MVFR to IFR ceilings currently ongoing at HNB/LEX/RGA, with BWG/SDF
staying VFR. The mix of clouds has helped keep flog mostly in check,
although can`t rule out a brief vis reduction still this morning
around sunrise.

Surface winds will be pretty light and variable through this period
given the wavering weak frontal boundary across the area. After some
improvement through the morning, VFR conditions will return.
Afternoon and early evening forecast brings some chances for showers
or a storm to return, but will be scattered in nature. Included
Prob30s for this threat.

&&

.LMK WATCHES/WARNINGS/ADVISORIES...
KY...None.
IN...None.

&&

$$

SHORT TERM...BJS
LONG TERM...EBW
AVIATION...BJS