836
FXUS63 KLMK 250550
AFDLMK

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

...Updated Aviation Discussion...

.KEY MESSAGES...

*  Drought-easing rainfall is likely late in the week as the
   remnants of Helene move into the region Friday.

&&

.UPDATE...
Issued at 930 PM EDT Tue Sep 24 2024

Coverage of showers and storms is now only isolated, and we`re not
expecting any more organized convection overnight.  However, the
atmosphere remains quite muggy and the flow aloft is cyclonically
curved. Therefore we can`t rule out additional isolated showers
through the night, especially east of I-65. Overall will knock
precip chances down a category from the previous forecast.  Update
on the way shortly.

Issued at 713 PM EDT Tue Sep 24 2024

Convection has decreased significantly in coverage and intensity, so
we have dropped the Severe Thunderstorm Watch. An isolated storm or
two is still possible this evening, but further severe weather is
not expected.

Issued at 505 PM EDT Tue Sep 24 2024

Scattered showers and storms continue generally east of I-65 ahead
of a cold front stretching from around Paoli to Hardinsburg to
Russellville. There`s still enough CAPE and bulk shear to support
convection, but with weak DCAPE, weak to moderate lapse rates, and
the 5H speed max moving off into eastern Kentucky, the storms are,
for the most part, not as strong as they were earlier. One exception
to this is a cell heading in the direction of Lake Cumberland in an
area shown by BNA ACARS to have relatively stronger instability and
low level lapse rates.

Will keep most of the Severe Thunderstorm Watch going for now, other
than shaving a few counties off of the western edge. More wholesale
canceling of counties should take place in the next 1-2 hours.

&&

.SHORT TERM /THROUGH THIS AFTERNOON/...
Issued at 315 PM EDT Tue Sep 24 2024

Breaks in the clouds allowed enough destabilization to support the
development of showers and storms this afternoon in a corridor of
1.7" precipitable water air ahead of a cold front and 5H speed max
ejecting out of an upper trough over Illinois. Scattered convection,
some robust, will continue for a few more hours and then gradually
decrease in coverage and intensity mid-late evening. The cold front,
slicing through southwest Indiana and western Kentucky this
afternoon, is moving only very slowly as its parent low moves NNE
through Michigan`s lower peninsula. Showers will remain in the
forecast through the night in the eastern parts of central Kentucky
and southern Indiana ahead of the front.

With efficient rain producers moving roughly parallel to the front,
training storms may lead to minor local flooding issues in a few
spots, especially along and east of a Bowling Green - Bardstown -
Cynthiana line.

As winds go nearly calm tonight in a moist, stagnant lower
atmosphere tonight, some patchy fog may develop late. However, a low
stratus deck is expected to form after midnight and continue into
Wednesday morning, limiting fog density and coverage.

Tomorrow the front will weaken as the Michigan low pulls away into
Canada. Instability will be significantly limited by widespread
clouds and scattered showers and the 5H shortwave trough will take
on a more positive tilt. While showers and a few storms are still in
the forecast for tomorrow, with the best chances east of I-65,
strong or severe storms are not expected. Will go with high
temperatures in the middle and upper 70s, which is slightly cooler
than the model consensus given the widespread overcast and some weak
cold air advection behind the surface front.

&&

.LONG TERM /TONIGHT THROUGH TUESDAY/...
Issued at 315 PM EDT Tue Sep 24 2024

Overall high confidence in abundant rainfall late this week, but
quite a bit less confidence with regard to exactly where, when, and
how much.

Upper low slowly digging southward from near New Madrid to Memphis
Wed night and Thu is a favorable setup for a predecessor rainfall
event (PRE) especially as the SSE flow aloft phases with the flow
around Helene, which will still be in the Gulf of Mexico at that
time. Will ramp up rain chances during the day on Thursday, but at
this point it appears the better focus for heavy precip will remain
south of Kentucky through Thu evening.

During Thursday night the two cyclones begin to Fujiwhara around
each other, with the upper low being drawn southward into Louisiana
as Helene advances through Georgia. Deep east-southeast flow will
draw copious moisture into the Tennessee and Ohio Valleys, with the
best window of opportunity for widespread and heavy rainfall from
late Thu night through Fri evening. Minor/nuisance flooding is
possible with the heavier intervals of rain, especially if there is
an initial round of heavy rain associated with the non-tropical low.
Wind fields could also support a SVR threat, but that remains quite
uncertain at this time. Sfc winds will get a little breezy as the
low-level center of circulation drifts into the Ohio Valley, with
speeds at 15-25 mph and a few 30 mph gusts likely.

Confidence trends down again on Saturday as the two lows eventually
merge. Rain chances will continue through the weekend, with some
potential for more focused training of showers and storms that could
result in localized flash flooding if parts of the area are getting
repeated heavy rainfall.

Rainfall totals by the time all is said and done will generally run
2-4 inches, with localized 5+ inch amounts possible. Short-fuse
flooding is likely during or just after the heaviest rain, but long-
fuse river flooding would require us to hit the high end of the
range of rainfall forecasts.

&&

.AVIATION /06Z TAFS THROUGH 12Z THURSDAY/...
Issued at 149 AM EDT Wed Sep 25 2024

Expecting deteriorating conditions at the TAF sites early this
morning as low ceilings and some vis restrictions in fog will both
be possible. In addition, some scattered showers are expected to
mainly affect LEX/RGA this morning. Expecting MVFR (and possibly
down to IFR) ceilings over the eastern TAF sites, with fog not as
prominent. Meanwhile, the central TAF sites of SDF/BWG will have the
better chances of low MVFR or IFR visibilities in fog. Some MVFR
stratus is also possible, but not as prominent as farther east.

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. After
and early evening forecast brings some chances for showers to
return, but will be scattered in nature.

&&

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

&&

$$

UPDATE...RAS/13
SHORT TERM...13
LONG TERM...RAS
AVIATION...BJS