002
FXUS63 KLMK 231755
AFDLMK

Area Forecast Discussion
National Weather Service Louisville KY
155 PM EDT Mon Sep 23 2024

...Updated Aviation Discussion...

.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 1141 AM EDT Mon Sep 23 2024

This morning, a decaying sfc cold front is located along the Ohio
River, with pooled low-level moisture in the vicinity of the front
bringing stratus and a few light rain showers/sprinkles to portions
of the FA. This has held temperatures in the 70s across the area,
with the exception of far southern KY, where more sunshine has
broken out this morning. More breaks in the clouds are showing up on
the latest satellite imagery over the Bluegrass region, so would
expect temperatures to increase there over the next hour or two as
well.

Across western KY and back into the mid-Mississippi Valley, moist
mid-level SW flow is lifting up and over the sfc front, contributing
to the development of waves of showers and storms. The leading wave,
which has not been handled particularly well in hi-res guidance,
should approach our SW IN and NW KY counties over the next 1-2
hours. The current thinking is that this wave of precipitation (and
associated increase in clouds) should initially help to keep us more
stable across the northern half of the FA this afternoon. As a
result, still think the best chance for convective development this
afternoon and evening will be across south central KY, where the 12Z
HREF mean shows 1500-2000 J/kg SBCAPE developing. Farther north,
shower/storm potential is more uncertain, though the lingering sfc
boundary may provide a source of lifting for convection.

Mainly just freshened the near-term grids at this time and made
minor PoP changes to handle this leading wave.

=====================================================================

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 /18Z TAFS THROUGH 00Z WEDNESDAY/...
Issued at 155 PM EDT Mon Sep 23 2024

A cold front continues to be draped across the region this
afternoon, and waves of precipitation are riding along this boundary
from west to east. The main area of precipitation will impact HNB
and SDF over the next few hours, with more scattered showers and
storms expected elsewhere. Confidence beyond this initial wave of
precipitation is quite low, so have only included TSRA mention where
there is moderately good confidence. While VFR conditions are
expected outside of any heavy rain/storms through much of the
forecast period, reduced ceilings and visibility would be possible
Tuesday morning around sunrise, though confidence is also low in
this. Winds will begin to pick up out of the south and southwest
Tuesday morning, with stronger gusts expected Tuesday afternoon.

&&

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

&&

$$

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