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257
FXUS63 KLMK 060030
AFDLMK

Area Forecast Discussion
National Weather Service Louisville KY
830 PM EDT Sun May 5 2024

.KEY MESSAGES...

*   Isolated showers and thunderstorms are possible today, mainly
    south and east of the Western KY/Bluegrass Parkways. More
    widespread rain chances return tonight into Monday.

*   Potential for multiple rounds of strong to severe storms next
    Tuesday through Thursday. Although confidence in timing remains
    low, all severe hazards will be possible.

*   Localized flooding potential will exist where repeated rounds of
    heavy rainfall occur next week.

&&

.UPDATE...
-- Changed Discussion --
Issued at 830 PM EDT Sun May 5 2024

Skies were partly cloudy across the region this evening with
temperatures in the the lower 70s.  Regional radars show an arcing
line of convection from Paducah southeast to just south of
Nashville, TN.  This activity has been steadily moving northward
through western TN this evening.  The convection has shown a slight
decrease in intensity over the last half hour with CG lightning
rates continuing to diminish.  Airmass out ahead of the front is
still slightly unstable, but with the onset of nocturnal cooling,
continued boundary layer stabilization is likely to take place
leading to this convection to become more elevated with time.

Nonetheless, activity is forecast by the high resolution models to
continue to hold together while moving northward overnight resulting
in most locations seeing some rainfall overnight.  Overall character
of the convection overnight looks to be more showery in nature with
some embedded thunder here and there.  Current forecast has this
well handled at this time.  Updated products have been sent.
-- End Changed Discussion --

&&

.SHORT TERM /THROUGH MONDAY/...
Issued at 305 PM EDT Sun May 5 2024

This afternoon... The cold front will continue to push through the
region. Along and ahead of the boundary, showers and storms have
developed due to moisture convergence and instability growth. With
sunset, these showers and storms will dissipate. Heavy rain, gusty
winds, and lightning are the main threats with stronger pulse
storms.


Tonight and Monday... A mid-level shortwave trough will move over
the Ohio Valley bringing some additional moisture, cyclonic
vorticity advection, and a weak LLJ. These conditions will allow for
widespread showers and embedded storms to move into the region from
southwest to northeast. Given that these storms will occur in the
overnight hours and have quite limited instability, there will be
little to no severe weather threat tonight. Low temperatures will be
similar to the previous night in the low-mid 60s.

Showers and storms will continue through Monday. Instability will
grow into the afternoon hours, however, values will remain mostly
marginal given weak mid-level lapse rates. Very little shear, 1.6-
1.8 inch PWATs, and DCAPE values around 600-800 J/kg will lead to a
pulse thunderstorm environment where strong wind gusts are possible
with a water-loaded downburst. Given high PWATs and high low-mid
level relative humidity, efficient rain production will lead to
around 0.75 - 1.25 inches of rainfall through Monday afternoon. Some
localized areas that see strong storms or a downburst may see higher
QPF. Main threats with strong storms will be gusty winds, heavy
rain, and lightning. Winds will be light and veering from the
northeast to the southwest through the day. High temperatures will
be in the upper 70s and reaching 80 in southern Kentucky and the
metro areas.

&&

.LONG TERM /MONDAY NIGHT THROUGH SUNDAY/...
Issued at 305 PM EDT Sun May 5 2024

Monday Night - Thursday...

Main Message/Broad Overview...

Active mid week timeframe shaping up as several waves eject out over
our region from a broad western CONUS trough. Expecting to have
periods of moderate to strong instability coupled with sufficient
deep layer shear to support organized convection, including
potential for some supercells. As a result, all severe modes will be
in play at times, along with a potential flooding threat that could
develop later in the mid week time frame, especially with repeated
rounds of heavy rain. Damaging winds and large hail are expected to
be the most common threat throughout, but again, all severe modes
could come into play at times.

Current focus is on three main waves. The first would be mid to late
morning Tuesday into early afternoon mainly across the northern half
of the CWA. Additional convective development is then expected later
Tuesday evening into Tuesday night, mainly along and south of the
Ohio River. The third wave would then be expect Wednesday evening
into Wednesday night.

Wave 1 Late Tuesday Morning/Early Tuesday Afternoon...

A warm front will lift north of our area Monday night, with
scattered showers and storms possible in the warm advection regime
over our area. Forecast soundings would suggest this convection will
be elevated in nature, with perhaps some hail with the strongest
cells. Overall, severe threat would be quite low outside of an
isolated hail instance, and most of that is dependent on mid level
lapse rates steepening toward dawn.

By sunrise Tuesday, upstream convection ahead of a cold front
extending from a strong northern Plains surface low will be poised
to enter our western CWA. Will be interesting to see how this plays
out as the ongoing convection could outrun the best shear profile,
especially if it gets a good lower level cold pool going. Another
plausible scenario would be an ongoing severe weather threat as a
line of showers and storms enters the CWA amid an increasingly
favorable vertical shear profile beneath the exit region of strong
mid/upper level jetting and a modest low level jet. Main threat
would be damaging winds along with a hail and tornado threat, mainly
across the northern half of our CWA.

Another wave of severe storms could redevelop across our region
later Tuesday night as the cold front impinges upon the area. Low
confidence in exactly how this plays out as previous convection
could play a factor. Nevertheless sufficient instability, sufficient
deep layer shear, and an approaching cold front all suggest that
severe weather would be possible. Certain models develop convection
across our area for much of the nigh, so something to watch.

A final, and probably the most concerning, round of severe weather
then looks to be on for later Wednesday evening into Wednesday
night. The main shortwave energy begins to eject out into the upper
Midwest on Wednesday night with an associated surface low moving
from the mid Mississippi River Valley to the Wabash River Valley.
Strong instability on the order of 2500-3000+ J/KG (even on GFS
soundings) will likely build during the day, and then be available
(at least MUCAPE values above a slight near-surface inversion) as
upstream convection builds and then moves through our region. The
05/00z run of the C-Shield model depicts a strong linear feature
diving through the CWA that would likely carry a widespread damaging
wind threat, large hail, some embedded tornadoes possible as well.
Forecast soundings are ominous as they show big CAPE profiles in the
presence of strong deep layer shear (both speed and direction)
yielding curved hodographs (Effective SRH 300+ M2/S2). Supercell
structures could easily accompany any linear feature, either
embedded or more discrete. Depending on how many waves of convection
materialize before this, we could see a Flash Flooding threat evolve
by this time as well.

Alternate scenario offered by the 05/12z ECMWF would suggest
convection will continue across our southern CWA into Wednesday, and
continually be convectively reinforced. This would limit the
northward progression of the warm front, and shut down much of our
severe chances across the northern half of the CWA for Wednesday
night into Thursday AM. Instead, severe and flood threat would
continue across our south CWA into TN. Meanwhile, the best forcing
and triple point would be across central IN where more severe
weather would develop. This bi-modal solution has happened in the
past with southern convection robbing our region, and meanwhile a
secondary and likely tornadic event unfolds to our north. This
secondary solution will continue to hurt confidence a bit in exactly
how this all plays out, at least for this forecast cycle.

Overall, still a lot that has to happen between now and then, but
concern is growing for what could be a significant event late
Wednesday/early Thursday if some of the current data verifies. Stay
up to date of the latest forecasts.

Thursday - Sunday...

Confidence lowers significantly in the late week/weekend time frame
as a messy upper pattern likely swings a couple more disturbances
through our area. Overall, temps be cooler in the 60s/70s with best
chances for a shower or storm on Friday and Saturday night/Sunday.
Quite a few ensemble members point to Saturday being one of the
`coolest` days we`ve had in a while as highs struggle to climb into
the upper 60s and overnight lows fall into the 40s.

&&

.AVIATION /00Z TAFS THROUGH 06Z TUESDAY/...
Issued at 707 PM EDT Sun May 5 2024

For this evening, VFR conditions with light and variable winds are
expected.  Later this evening, a band of convection ahead of a mid-
level wave will bring an arcing band of showers and storms into the
region from the SW.  These should impact KBWG around 06/03-04Z and
then get into KSDF/KHNB/KLEX in the 06/07-09Z.  Highest confidence
in thunder is at KBWG for now as confidence for thunder chances
decreases with northward extent.  However, rain showers will affect
the northern terminals late tonight through tomorrow morning.  Cigs
will start off VFR but then decrease into the MVFR range overnight
and into Monday morning while winds gradually shift to the southeast
toward dawn.

&&

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

&&

$$

UPDATE.......MJ
SHORT TERM...SRM
LONG TERM....BJS
AVIATION.....MJ