419
FXUS63 KLMK 231324
AFDLMK

Area Forecast Discussion
National Weather Service Louisville KY
924 AM EDT Mon Sep 23 2024

.KEY MESSAGES...

*  Multiple waves of scattered showers and storms are expected
   this afternoon through Tuesday night. There is a low chance
   for strong to severe storms today and Tuesday.

*  Unsettled weather is a possibility into late week with the
   remnants of a tropical system potentially moving into our region.

&&

.UPDATE...
Issued at 923 AM EDT Mon Sep 23 2024

Made a minor change to near-term PoPs to account for scattered
warm advection showers which have developed across western KY over
the past hour or two. Would expect these showers to continue moving
through western portions of the FA over the next few hours, and have
increased PoPs accordingly. Otherwise, the forecast remains on track
at this time.

&&

.SHORT TERM /THROUGH TONIGHT/...
Issued at 308 AM EDT Mon Sep 23 2024

Early This Morning...

A weak frontal boundary remains draped southwest through the Lower
Ohio Valley and into the Ozarks early this morning. While convective
activity is at a minimum this morning, we do have a smattering of
showers in the Bluegrass in an area of weak convergence and along
the Theta-e ridge. These showers will continue to move east out of
the area over the next hour or so. The morning hours will remain
fairly quiet, although we cannot rule out spotty rain in a moist
airmass with a weak boundary cutting through it. PW values are
around 1.6-1.8 inches, and that will remain fairly steady into
tonight.

Today and Tonight...

An upper level shortwave trough (well-defined on water vapor imagery
over the KS/NE border) over the central Plains this morning will
swing east to the Mid-MS River Valley by tomorrow morning. An S-
shaped upper level jet structure snaking from the southern Plains to
Great Lakes will translate eastward, providing increasing diffluence
aloft this afternoon into tonight over the Ozarks, Mid-MS Valley,
and Lower OH Valley. Weak sfc wave development appears likely in the
vicinity of the Ozarks later today, with the deepening low then
lifting northeast into IL by tomorrow morning. This coincides with
the development of a 30-35 kt SW low-level jet tonight over the Mid-
MS and Lower OH Valleys.

As for sensible weather, the morning looks mostly cloudy and
relatively dry with only spotty/isolated showers. The large scale
forcing is strongest off to our west during the daytime.
Southwesterly mid-level flow begins to increase slightly this
afternoon, but it`s not until tonight that we see more robust
southwesterly low-level and mid-level winds nose into the region
ahead of the approaching shortwave trough. Nevertheless, the chance
for scattered showers and thunderstorms will increase as upstream
convection drifts east into the forecast area and we see at least
some new development overhead.

It appears there could be a brief window of clearing later today,
especially from south-central KY into the Bluegrass Region, which
would boost sfc heating and low-level destabilization. However,
confidence is low in the degree of clearing. Significant cloud cover
will still likely play a role in limiting sfc warming. HREF means
and probabilities point to the southern half of central KY as the
area most likely to realize SBCAPE > 1000 J/kg. And with a modest
uptick in deep-layer shear to 25-30 kts, this environment could
support a few strong to marginally severe storms. But with stronger
wind fields still off to the west, a loosely organized multicellular
storm mode is anticipated. The main hazards are brief heavy
rainfall, locally gusty winds, lightning, and small hail.

Afternoon highs will range from the upper 70s to lower 80s in
southern IN to the mid 80s in south-central KY. Isolated to
scattered showers/storms will remain possible into tonight. Rain
chances ramp up considerably early Tuesday, especially across the NW
half of the forecast area, with the arrival of the LLJ and
approaching upper level trough. Brief heavy rain, lightning, and
gusty winds are possible overnight into Tue morning. Lows will be in
the 60s.

&&

.LONG TERM /TUESDAY THROUGH SUNDAY/...
Issued at 308 AM EDT Mon Sep 23 2024

A rather unsettled and increasingly wet forecast is in store for
later this week.  A trough of low pressure aloft is progged to get
separated from the main jet stream flow and become cut off over the
Mississippi river valley Tuesday/Wednesday.  This rotating
disturbance will not make much eastern progress, which will bring
chances for showers and thunderstorms.  The current forecast has
between 0.25 and 0.75 inches of potential rain Tuesday into
Wednesday.  At the surface, a cold front will move through the
region Tuesday afternoon and evening.  With decent model soundings
depicting available instability and shear, the possibility for
strong to severe storms is possible.

Models are coming into better agreement as to the progression of the
tropical cyclone forecast to arrive onshore in Florida Thursday
afternoon/evening.  ECMWF and GEFS ensemble forecasts have similar
average tracks brining the remnants of the system into Kentucky &
Indiana, bringing more chances for showers and thunderstorms. For
southern Indiana, anywhere between 0.50" and 1" of rain totals are
forecast Thursday through next weekend, while central Kentucky could
see anywhere from 1" to 2.5" of rain.  While it`s still too early to
tell the exact storm track and certainly things can change between
now and Thursday, early model atmospheric profiles look fairly
stable with warm layers aloft (albeit very moist with PWs between
1.5 and 2"), which would limit any severe weather potential. High
temperatures in the afternoon will be in the upper 70s to lower 80s,
which is right around normal for late September.

&&

.AVIATION /12Z TAFS THROUGH 18Z TUESDAY/...
Issued at 701 AM EDT Mon Sep 23 2024

A weak sfc boundary remains draped southwest through the Lower Ohio
Valley early this morning. Partial clearing overnight has led to
some patchy fog, most notably at LEX currently. Expect improving
visibility at LEX around or shortly after 13Z. Some IFR and low-end
MVFR stratus has also attempted to push south into the region from
Indiana but has struggled to make significant progress. Most
terminals should avoid a BKN low ceiling this morning, but cannot
rule out brief lower ceilings.

The weather turns a bit wetter this afternoon into tomorrow. Expect
SCT SHRA/TSRA at times, which could bring brief heavy rainfall,
lightning, and locally gusty winds.

&&

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

&&

$$

UPDATE...CSG
SHORT TERM...EBW
LONG TERM...MCK
AVIATION...EBW