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518
FXUS63 KLMK 251948
AFDLMK

Area Forecast Discussion
National Weather Service Louisville KY
348 PM EDT Sat May 25 2024

.KEY MESSAGES...

*   Severe storms possible Sunday into Sunday night. Main hazard is
    damaging winds with localized hurricane-force gusts possible.
    Tornadoes, large hail, and flooding cannot be ruled out either.

*   Unsettled pattern will continue into Monday with additional
    shower and thunderstorm chances.

&&

.SHORT TERM /THROUGH SUNDAY NIGHT/...
-- Changed Discussion --
Issued at 348 PM EDT Sat May 25 2024

We continue to focus on the severe weather potential for tomorrow
which continues to transition as it comes into better focus. A few
days ago when global models were the only models to have Sunday in
range, hodographs looked ominous. There was a lot of synoptic
forcing, tons of instability, and high levels of shear at all
levels. Tornadoes looked favorable. Then, as the NAM picked up on
Sunday, it showed one or two line segments extending south out of
central Indiana into southern Indiana and north central Kentucky,
but it wasn`t too impressive. Now that the CAMs have had multiple
runs that have captured tomorrow`s events, the forecast continues to
get fine tuned. Every model doesn`t agree on the exact timing, but
the general idea is pretty strong among the models.

Tonight, upper flow is mostly zonal. There is a little bit of a
trough over the Southern Rockies and a little ridging over New
England. Extending south from near Chicago, surface high pressure
extends through Kentucky while a surface low sits over western
Kansas, and as upper flow begins to push the surface low east to
east-northeast, the system is expected to send a line of convection
over the Plains. By Sunrise, the line is expected to be crossing the
Ozarks and Midwest as it surges towards the Lower Ohio Valley.

Around 15-16z Sunday morning, the line is expected to begin
impacting the western edge of the CWA. As it will be late morning,
there could still be some low level stability. Low level lapse rates
are marginal in the 7.5 C/km range, but the main driving force at
this time will be the system`s cold pool. After the line has
traveled all night, the cold pool is expected to be ahead of the
main line. This could help to decay the line as it moves west to
east over the CWA, but as it begins to enter areas on the the
eastern side of the CWA, including the Bluegrass and Lake Cumberland
regions, some afternoon heating could help increase lapse rates to
8.5 C/km or more. This could help to intensify the line into the
later afternoon. The line is expected to be near Louisville around
17-18z and east of the CWA by around 20-21z.

The main thing this line has working for it is instability. MLCAPE
values ahead of the line will begin in the 2,000 J/kg range and
increase to around 2,500 J/kg over southern Indiana and up to 2,700
J/kg over southern Kentucky. MUCAPE values will begin around 2,500
J/kg and increase to near 3,300 J/kg. Low level shear is only
marginal with 0-1km SRH around 90. A tornado can`t be ruled out, but
chances are fairly low. The main threat will be gusty winds from the
storms downdrafts. With the high levels of instability, the
strongest cores could also produce hail. Another concern will be
flash flooding. With all the rain we have had lately, mainly over
southern Kentucky, flash flood guidance is low. Don`t believe the
north to south oriented line will cause too many flooding issues as
the dwell time over any one spot will be limited. There is a chance,
mainly over southern Kentucky. That some storms could develop behind
the line and drop to the south, so if any location gets multiple
rounds or sees training storms over the same area, flash flooding
will likely occur.

With the first line of convection outrunning the surface low, a
second line is expected to develop early tomorrow night just ahead
of the low. It could begin to enter our Indiana counties by around
4z Monday, and Kentucky counties an hour or two later. This second
line won`t be as mature as the first line, so the convection should
stay on the leading edge of the convection which could help overcome
the near surface inversion given the time of day. It also looks like
instability could be more limited, but low level shear will be much
higher with this second wave. 0-1km SRH will approach 400 under a 50
knot low level jet. The high LCLs above 1km and stable low levels
are reasons against tornado development, but strong low level shear
in a convective environment could help to produce a spin-up. Believe
the chances for a tornado will be greater in this second line
compared to the first line, but gusty winds will be the main threat.
The threat of hail will be less in the second line given the much
lower instability. The line will likely begin to dissipate before
the line exits the CWA by at least 9z.
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&&

.LONG TERM /MONDAY THROUGH SATURDAY/...
-- Changed Discussion --
Issued at 348 PM EDT Sat May 25 2024

Monday through Tuesday Night...

Surface cold front is still forecast to push through the region
during the day on Monday which will bring an end to the severe
threat locally.  Now the upper level trough axis will remain across
the region, so some convective redevelopment is likely during the
afternoon across the region.  Some stronger storms can`t be ruled
out across our east during the afternoon.  Highs on the day will
range from the upper 70s to the lower 80s.  Breezy conditions will
be seen as well on Monday with sustained winds of 10-15 mph with
occasional gusts to 20-25 mph at times. Drier air will filter into
the region by Monday night and dry/tranquil weather is expected
through the remainder of this forecast period.  Lows Monday night
will be upper 50s to around 60.  Highs on Tuesday will be in the
upper 70s to the lower 80s with overnight lows in the mid-upper 50s.

Wednesday through Saturday...

Upper trough axis will push east of the region by Wednesday and
heights will gradually build into the day on Thursday.  Toward the
end of the week, the pattern looks to become a bit more blocked as
the east coast trough closes off and becomes a closed low just south
of Maine.  Another shortwave trough axis will be pushing through the
Plains, while the Ohio Valley remains in a sharp but narrow ridge
axis.  Overall, the pattern for Wednesday through Friday supports
dry weather conditions.  Within the southwest flow by Saturday, we
could see some isolated/scattered storms fire, though the best
potential for rainfall looks to hold off until late Saturday night
and early Sunday.

Highs Wednesday and Thursday will be in the upper 70s to near 80,
with overnight lows in the low-mid 50s.  A few of our valley
locations could see temps dip into the upper 40s each night.
Temperatures will warm a bit by Friday as readings rise into the
upper 70s to the lower 80s.  Mainly lower 80s are expected by
Saturday.
-- End Changed Discussion --

&&

.AVIATION /18Z TAFS THROUGH 00Z MONDAY/...
Issued at 212 PM EDT Sat May 25 2024

A cold front has dropped to near the Ohio River. This has brought a
layer of stratus to HNB and near SDF. Model guidance has tried to
dissipate and lift this cloud cover all day, but the layer seems a
little more persistent. Southeast of the stratus, cumulus extends
into the BWG and LEX areas, so for the next few hours, there could
be some bumping in-between MVFR and VFR levels. Outside of trying to
determine ceiling levels, things are fairly quiet. There is an
isolated chance that convection could impact SDF, LEX, or RGA this
afternoon/evening, but chances are low enough to leave out of the
TAFs. Tonight, LEX and RGA could see some limited fogging depending
on cloud cover.

&&

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

&&

$$

SHORT TERM...KDW
LONG TERM...MJ
AVIATION...KDW