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376
FXUS63 KLMK 240029
AFDLMK

Area Forecast Discussion
National Weather Service Louisville KY
829 PM EDT Thu May 23 2024

.KEY MESSAGES...

*   Stormy pattern with risks of strong to severe storms and
    localized flooding issues will continue into Monday.

*   The greatest threat for severe weather will likely come Sunday
    afternoon into early Monday morning ahead of a cold front.
    Damaging winds, large hail, and tornadoes will be possible with
    severe storms.

&&

.MESOSCALE...
-- Changed Discussion --
Issued at 829 PM EDT Thu May 23 2024

After coordinating with SPC/JKL/OHX, have allowed the Severe
Thunderstorm Watch to expire on time. Deep convection has abated and
although some gusty sub-severe winds will still be possible from
southeast Indiana into the Kentucky Blue Grass, the main issue over
the next few hours will be flooding. Even without strong
thunderstorms, a large area of rain associated with an MCV located
just south of Louisville has been very efficient, utilizing
precipitable waters around 1.5-1.6" plus slow forward movement. This
area of rain is expected to continue to push to the east and
northeast and exit central Kentucky between midnight and 2am.


Issued at 455 PM EDT Thu May 23 2024

A cluster of poorly organized thunderstorms is currently working WSW
to ENE across our region. Although we have seen an increase in
coverage over the past couple of hours due to the exit region of an
H3 jet overspreading the area, a couple of limiting factors are
hurting storm strength at the moment. 1.) Deep layer shear values
around only around 20-25 knots, which is generally supportive of
weakly organized multicell storm modes. A few brief instances of
supercell storm modes and deviant motion have shown up, but overall
mode remains erratic given the lack of a stronger 0-6 km shear
vector. 2.) Mid level lapse rates around only around 6.5 C/Km, and
don`t look to improve much with time. So, given that we have seen
the arrival of stronger forcing, and don`t seem to gain much
instability from here forward, don`t expect intensity to gain much
more. One thing that could change that would be an added 5-10 knots
of deep layer shear, but don`t really see that occurring before
storms exit our area either.

As a result, expect storms to mostly stay in the sub-severe range
with gusty winds and only small hail. We are seeing some briefly
torrential rainfall rates in the 2-3" per hour range (although keep
in mind those rates will only last 5-10 minutes at a time). This may
cause some localized flooding concerns through the evening, however
it wouldn`t take much from a training or repeated storm impacts
perspective to push some areas into the Flood Advisory or localized
Flash Flood Warning realm. Continuing to monitor.

Severe Thunderstorm Watch 293 remains in effect for  the eastern
half of our CWA through 8 PM EDT, however expecting only isolated
instances of severe potential as we work through the early evening
hours.
-- End Changed Discussion --

&&

.SHORT TERM /THROUGH FRIDAY/...
Issued at 329 PM EDT Thu May 23 2024

Satellite imagery currently shows a window of clear skies over parts
of central and eastern Kentucky. This clearing began farther west
and has now pushed to its current location. It was also one of the
driving forces for the recently issued Thunderstorm Watch over parts
of central and eastern Kentucky (which runs until 8 PM EDT), as well
as areas to the south in Tennessee. As with most of the CWA,
including southern Indiana and central Kentucky, we continue to see
weak shear overall, but there is some instability. MLCAPE values are
just shy of 1,500 J/kg, and MUCAPE values are over 2,000 J/kg. Lapse
rates and DCAPE values are marginal, around 7.5 C/kg 0-3km and
around 800 J/kg respectively. We likely won`t see widespread severe
weather with huge hail stones or extreme high winds, but conditions
should produce 1" hail with some gusty thunderstorm winds. This
activity will work east over the CWA and is expected to be east of
our area early tonight.

Tonight, we maintain mostly zonal flow overhead with a large surface
low over the Western Plains. Farther east, over the Lower Ohio
Valley, pressure gradients remain loose, so southerly winds will
remain light. Guidance is somewhat mixed with how much skies will
clear, but with low level moisture in place and with saturated
grounds, fog and/or low stratus is expected over much of the region.
Low temperatures are expected to drop into the low to mid 60s.

Tomorrow, south winds remain light as zonal flow begins to push a
cold front east across the Plains towards the CWA. Moisture rich air
will remain over the region throughout the day. With precipitable
water values between 1 to 1.5", a low chance of precipitation will
be carried during the day. Any morning stratus and fog could be slow
to clear before sunshine becomes more likely closer to midday. This
would help to increase low level lapse rates and instability ahead
of an approaching line of expected evening convection which is
mentioned in the long-term discussion. High temperatures are
expected to reach into the upper 70s to mid 80s. Most will see the
low 80s.

&&

.LONG TERM /FRIDAY NIGHT THROUGH THURSDAY/...
Issued at 329 PM EDT Thu May 23 2024

A frontal boundary will come sliding toward the region Friday night.
Models vary on convective development/persistence ahead of the
front, but some show convection pushing into the region Friday
evening into the overnight hours. The severity of this feature will
be somewhat conditional on its arrival time... an earlier arrival
time would favor an atmosphere with less CIN and more instability,
while a later arrival would feature less favorable parameters for
severe storms. PoPs overnight are generally highest in the early
part of the period, with a tapering down toward dawn Saturday.

The frontal boundary will slow down and stall near the Ohio River on
Saturday. Isolated to scattered showers and storms may develop along
and ahead of the frontal boundary Saturday though shear will be
quite weak (0-6km shear less than 20kts) so storm severity potential
should be very limited.

After a lull in precipitation Saturday night, additional showers and
storms will accompany a surface warm front as it lifts into the CWA
Sunday morning while a strong 850mb LLJ advects in rich, Gulf of
Mexico moisture into the region behind it. Our region should be well
within the warm sector by Sunday afternoon and be in an environment
of strong shear (both low level and deep layer) as well as moderate
instability. Multiple rounds of storms are possible Sunday afternoon
into Sunday night, but the most widespread activity will likely
arrive late Sunday afternoon into Sunday night as a cold front
pushes in from the west. While there are some factors that could
hamper the impactfulness of this event (i.e., destabilization
between waves of showers/storms, strength of capping inversion,
etc), the overall synoptic environment is one that would support
organized convection capable of damaging winds, large hail, and
tornadoes with severe storms. Joint probabilities from the
GFS/Euro/Canadian ensembles show >70% chances of SBCAPE exceeding
40kts and 0-6km shear exceeding 40kts over a large portion of the
region Sunday into early Monday morning. If everything comes
together just right, this could be a potentially significant event.
As such, the SPC Day 4 Outlook seems justified given the potential.

Some shower and storm activity could continue into Monday as the
frontal boundary slowly sags southward, though activity for Memorial
Day should be non-severe. Cooler conditions with lower dewpoints
will then persist through much of next week. Can`t rule out periodic
shower chances after Memorial Day, though the overall theme going
into next week is one that features drier/cooler weather.

&&

.AVIATION /00Z TAFS THROUGH 06Z SUNDAY/...
Issued at 746 PM EDT Thu May 23 2024

A cluster of showers and thunderstorms is currently moving eastward,
roughly along the I-64 corridor, impacting the SDF/LEX/RGA TAF
sites. SDF will be the first to see relief, with things clearing up
by 830 to 930 PM. Expecting improvement at LEX by 11 PM, and RGA by
Midnight EDT. Until then, visibilities could drop down to 1 to 2 SM
in heavy rain/TSRA, and briefly below 1SM is possible. Some gusty
winds up to 35 mph also can`t be ruled out.

HNB should be dry for the remainder of the overnight, and BWG could
see some light -SHRA for the next hour or so before going dry.

Do expect some clearing of skies later tonight, and that combined
with light and variable winds and recent widespread rainfall will
likely lead to some fog formation. Some models hint at it being more
of a low stratus setup, so have covered both threats with a temps in
the pre-dawn through sunrise hours. Could end up being a dense fog
setup if we do see persistent clearing.

Otherwise, look for improvement by mid morning with steady SSW winds
taking hold. Any lingering MVFR vis/cigs should trend toward VFR by
late morning/midday, if not sooner. Another round of storms could
arrive by the end of this TAF cycle, but will handle that with
future updates.

&&

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

&&

$$

MESOSCALE...13/BJS
SHORT TERM...KDW
LONG TERM...DM
AVIATION...BJS