373
FXUS63 KLMK 221452
AFDLMK

Area Forecast Discussion
National Weather Service Louisville KY
1052 AM EDT Sun Sep 22 2024

.KEY MESSAGES...

*  Warm and humid today, with scattered afternoon and evening
   thunderstorms ahead of a cold front.


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

&&

.UPDATE...
Issued at 1052 AM EDT Sun Sep 22 2024

An area of showers and a few rumbles of thunder continues to move
along the Ohio River west of the I-65 corridor at this hour. This
complex has shown a weakening trend over the past 30 to 45 minutes,
with warming/steady state cloud top temperatures on IR satellite and
a decrease in lightning observed in addition to a drop in
reflectivity. With outflow from this cluster now well ahead of the
reflectivity, weakening of cells should continue, though as we
destabilize later this morning and into the afternoon, new
development along this boundary will be possible. Evidence of
redevelopment is already showing up across western KY at this hour,
though it is uncertain how long this will be sustained as these
cells drift into an environment worked over by earlier convection.
Increased clouds from this area of precipitation should hold
temperatures down somewhat along the Ohio River, and we`ve gone
ahead and nudged temps down a degree or so for later today.

In much of southern and eastern portions of the FA, mostly sunny
skies continue at this hour, assisting temperatures in warming into
the low 80s at this hour. As a result, there will likely end up
being a NW-SE gradient in temperatures later today, with
temperatures farther to the southeast having a much better chance to
reach the upper 80s and lower 90s this afternoon.

Updated forecast products will be sent shortly.

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

Issued at 852 AM EDT Sun Sep 22 2024

A cluster of heavy showers, possibly with embedded thunder, has
developed between Henderson and Owensboro over the past hour, and is
ahead of the main area of precipitation. Have increased near term
PoPs over western portions of the FA to account for this
development. While this activity has developed in a fairly stable
near-sfc environment, it appears that outflow running ahead of
activity to the NW is lifting parcels to the LFC aloft, so there`s
no reason to suspect this convection won`t sustain as it moves to
the east later this morning. Otherwise, no changes to the forecast
at this time.

&&

.SHORT TERM /THROUGH TONIGHT/...
Issued at 331 AM EDT Sun Sep 22 2024

Radar is quiet early this morning in central KY and southern IN, and
skies are mostly clear. There is plenty of action upstream across MO
and into western IL, where a convective complex is evolving eastward
near a sfc cold front. The sfc cold front extends NNE through
eastern IA, WI, and Lake Superior to a low over northern Ontario. A
warm, moist airmass is in place in the Lower Ohio Valley ahead of
the cold front, with sfc dewpoints currently in the mid/upper 60s.
The sfc cold front is forecast to approach the region from the
northwest today before sinking into the Lower Ohio Valley later this
evening. Mid and upper level ridging over the Ohio Valley will
deamplify today as the ridge axis slides east. This occurs as upper
level shortwave energy races east-northeast across the Midwest and
Lower Great Lakes.

The upstream convection is forecast to move into the region from the
west by midday or early afternoon (late morning in southwestern
Indiana). Some early day sfc heating/destabilization will take
place, though satellite imagery shows plenty of cloud cover
preceding the convection. The eastern two-thirds of the forecast
area will have the best chance at realizing SBCAPE > 1000 J/kg.
Overall, the complex will be in weakened state by its arrival. Some
additional development will be possible along the leading edge of
this activity. Scattered thunderstorms are likely this afternoon
into the evening hours. Deep-layer shear of only 20-25 kts will
limit convective organization and strength. The severe weather risk
is low, though cannot rule out locally gusty winds with a few
storms.

Moisture will increase just ahead of the sfc boundary with slightly
stronger southwesterly low-level flow. PW values increase to 1.8+
inches this afternoon, and a pool of moisture sinks south and east
over the Ohio Valley tonight along the frontal boundary. A general
lull is anticipated behind the first wave of showers/storms this
afternoon, but then additional isolated to scattered development
will be possible tonight given the position of the cold front and
rich moisture in place.

Short-duration bursts of heavy rainfall rates could produce brief
ponding on roads, increasing the risk for hydroplaning. However, the
overall flooding risk is low given the ongoing drought and
beneficial nature of any rains at this point.

We`ll see a relatively large temperature gradient from NE to SE
today. Areas further south and east that see more early day sun will
see temps climb into the upper 80s and lower 90s (south-central KY,
Bluegrass Region). Southern IN will only see highs in the upper 70s
and lower 80s. Tonight, lows will be fairly uniform in the mid/upper
60s.

&&

.LONG TERM /MONDAY THROUGH SATURDAY/...
Issued at 331 AM EDT Sun Sep 22 2024

===== Monday - Wednesday =====

Unsettled weather will be the main story for the first half of next
week, though the precip chances are much needed now that most of the
region is experiencing moderate (D1) to severe (D2) drought
conditions. We`ll start off Monday with a Marginal Risk for some
isolated strong to severe storms.

An upper shortwave trough will be digging over the central High
Plains on Monday, though still largely to our west throughout the
day. A meandering quasi-stationary front will be nearly parallel to
the Ohio River, keeping our Kentucky counties within the warm
sector, and the focus for any thunderstorm development to the south
of the river. There`s considerable uncertainty in the Day 2 outlook
due to the possibility of widespread cloud cover and perhaps some
ongoing precip Monday morning, which would end up limiting our
destabilization. With the upper trough axis still well off to our
west, overall forcing may end up being weak throughout Monday. We
may get our best convection chances from differential heating
boundaries within the warm sector Monday afternoon, and expanding
outflow boundaries would possibly fire up additional scattered
convection into the early evening hours. Gusty winds and small hail
would be the primary hazards with any stronger storm, in addition to
heavy rain and lightning.

By Tuesday, the upper shortwave will shift east across the central
US, which will ramp up the large-scale ascent and mid-level flow
overhead to roughly 50kts. Uncertainty also exists for Tuesday storm
potential, largely due to the lingering cloud cover that could limit
peak heating again. However, if (and it`s a big IF) we are able to
realize any considerable instability, our chances for severe storms
will be much higher, given the stronger forcing, enhanced mid-level
flow, and better deep-layer shear. Cloud cover plays a large role in
the uncertainty for severity, though being in a humid airmass, and
with the forcing expected, can at least expect some shower and storm
activity anyway for Tuesday. The question remains on whether we will
be unstable enough for strong to severe storms. Due to this, SPC has
noted that they will hold off on introducing any severe probs for
Tuesday at this time.

the upper shortwave will eventually slide east beginning on Tuesday
night and into Wednesday. This will help push the meandering
boundary east of our region on Wednesday. Slightly lower PoPs are to
be expected for Wednesday, but will have to hold onto higher chances
in our east as the front takes it`s time moving east.

Confidence on temps each day remain somewhat uncertain too, but
generally looking at upper 70s and lower 80s each day. Could end up
with some drastic differences on high temps, depending on cloud
cover, possible outflow boundaries, and of course the showers and
storms.


===== Thursday - Sunday =====

Models begin to diverge by Thursday, with differing solutions on the
evolution of the upper shortwave, and downstream from there.
Confidence remains very low for this time frame, and will take
several more days to gain any confidence. With a tropical system
coming into the Gulf of Mexico around this time period, interactions
between the mid-latitude flow pattern and this system could lead to
impactful weather across the region by late this week into next
weekend, though confidence in this is very low. Unfortunately, we
remain in a "wait and see" position at this time until models begin
to converge on a particular solution.

&&

.AVIATION /12Z TAFS THROUGH 18Z MONDAY/...
Issued at 712 AM EDT Sun Sep 22 2024

VFR and dry to begin this TAF period. SCT shra will approach HNB
during the midday hours, and cannot rule out isolated lightning
activity. SCT shra/tsra will be possible later this afternoon
through the evening hours, but limited coverage of tsra precludes
inclusion of TSRA at most TAF sites at this time. Timing remains
problematic given the lower confidence/lower coverage scenario. A
cold front will sink into the region tonight and will bring low
stratus and some reduced vsby to the region early Monday.

&&

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

&&

$$

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