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000
FXUS63 KLMK 170733
AFDLMK

Area Forecast Discussion
National Weather Service Louisville KY
333 AM EDT Wed Apr 17 2024

.KEY MESSAGES...

*   Showers and isolated thunderstorms are possible early this
    morning.

*   Conditional threat of severe weather this afternoon. Overall
    confidence remains low in any thunderstorm development.

*   Strong to severe storms possible Thursday evening and overnight.

*   Much cooler weather this weekend.

&&

.SHORT TERM /THROUGH THURSDAY/...
Issued at 332 AM EDT Wed Apr 17 2024

Synopsis...Broad upper-level low over southern Canada will absorb
shortwave energy moving through the Midwest causing the attendant
surface cyclone to quickly occlude and eventually deviate to the
north while trailing cold front loses momentum as it crosses the
forecast area later this afternoon and evening. Although the mid to
upper flow will remain relatively strong, the low-level jet will
weaken and remain confined to the Upper Ohio Valley.

Model Evaluation/Confidence...The 17/0Z run of parameterized and
convection-allowing models have continued to depict best storm
coverage farther north into Indiana and Ohio this afternoon and
early evening. Still, the most aggressive guidance (FV3/RRFS) show
sporadic discrete convection late in the afternoon east of I-75,
which cannot be ruled out at the moment. As a result, ML-based
(Nadocast/CSU) severe probabilities are fairly low and highlighting
hail as the primary hazard followed by damaging wind and tornado.
Main uncertainty in the forecast continues to be convective
initiation ahead of the cold front. In summary, there is a low,
conditional threat of severe weather late this afternoon and early
evening across the forecast area with best chances focused to the
east.

This morning...Elevated showers and sporadic storms are currently
translating across the forecast driven by moisture convergence
associated with the low-level jet. Although this activity should
continue through sunrise, limited instability due to warm
temperatures aloft and plenty of low-level dry air will prevent any
potential of severe weather or flooding. Rest of the morning will be
mostly dry with partly to mostly cloudy skies and non-thunderstorm
southerly winds gusting between 15-25 knots amid decent 0-1 km lapse
rates.

This Afternoon/Evening...Main forecast challenge for this period
will be forecast initiation ahead of the approaching cold front.
Although there will be moderate surface-based instability, strong
deep layer shear, steep mid-level lapse rates, and sufficient 0-1km
SRH for all severe hazards to occur, there are several factors
negatively impacting the probability of convective initiation.
First, potential for weaker forcing in the lower Ohio Valley as the
surface cyclone weakens/deviates and the cold front becomes more
diffuse to the south. Second, moderately strong capping inversion in
the 850-700 mb layer due to subsidence in the wake of the morning
precipitation wave. Third, substantial mid-level dry air entrainment
potentially impacting sustained deep moist convection. And finally,
high LCL due to mix-down processes amid gusty winds. That being
said, if deep convection occurs (mostly in a discrete mode), it can
quickly get strong and organized to exhibit rotating features. This
appears more likely to happen in the eastern portion of the CWA
(Bluegrass and Cumberland regions) where forecast soundings show
better moisture profile in the low levels and, therefore, lower LCL
and slightly higher mixed-layer instability. As mentioned in the
previous discussion, strong non-thunderstorm wind gusts of 25-35 mph
will be present in the afternoon.

Tonight...Even if storms do manage to develop in the afternoon,
overnight hours will be dry with winds shifting to the south.

&&

.LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/...
Issued at 332 AM EDT Wed Apr 17 2024

Thursday - Friday...

Most of Thursday looks dry and mostly sunny with a progressive mid
level ridge briefly controlling our weather. Do expect increasing
clouds (and perhaps some storms) later in the afternoon and early
evening, but not before we get quite warm. Have most temps peaking
in the 80 to 85 degree range with a little aid from a steady S wind
picking up in the afternoon.

Thursday evening/night remains a concern as a surface low tracks
from the mid Mississippi River Valley into central IN and OH. In
addition, an uptick in forcing is expected as a mid/upper level
impulse impinges on the region, and modest low level jetting around
30 knots responds. This appears to yield some sort of linear
convection across our area with perhaps some mixed storm modes
embedded throughout. The overall deep layer shear profile should
yield something around 35 knots in the 0-6 km layer, along with some
directional shear. Modest instability is also likely to be present,
although likely only in the 500-1000 J/KG range of ML CAPE by the
time convection arrives in our CWA. It should be noted that there
are some more aggressive solutions out there (like the NAM), however
instability is usually overdone. Something to watch as we move
closer as those solutions would likely yield a more ominous scenario.

Looks like a fairly quick hitting system that should mainly impact
our area between 00z and 09z. Overall fairly confident in timing,
but could see it shift 3 hours forward or back. At this time, the
main threats appear to be pockets of damaging wind, although can`t
rule out any of the other hazards at this time given the shear
profile and at least some expected surface/near surface based
instability to be present. SPC has brought a little bit more of our
area into the Slight Risk with the new Day 2 Outlook, and that seems
pretty reasonable given the setup.

We should be post-frontal by sunrise Friday with perhaps a few
lingering showers across our eastern CWA. Overall, expect a drying
trend from W to E through the day with max temps in the 65 to 70
degree range for most. Also expect some late afternoon and evening
sunshine after morning clouds steadily clear out. The sunshine will
be welcome as fairly stiff NW winds of 10 to 15 mph, gusting up
around 20 to 25 mph will likely make it feel a fairly chilly,
especially after our recent temps well into the 80s.

Friday Night - Sunday Night...

Looking for a mostly dry and much cooler weekend ahead as surface
high pressure builds in behind the front. Will continue with a dry
forecast with the caveat that some light precipitation could skirt
our southern CWA Saturday night or early Sunday morning as a
southern stream wave scoots by. Outside of that, the theme will be
the cooler temperatures with highs on Saturday mostly in the 60 to
65 degree range, and highs on Sunday only in the upper 50s to around
60. Overnight lows on Saturday night and Sunday night are also
expected to be quite chilly and only in the upper 30s and low 40s.

Monday - Tuesday...

Lower confidence by Monday and Tuesday as a couple of disturbances
could impact our area. The first would be a moisture starved and
progressive closed low on Monday. Will keep the forecast dry for
now, but may eventually have to add some low pops for a few rain
showers. Tuesday could bring a secondary shortwave quickly rotating
through the area, and with a bit more confidence in this feature in
the models, will carry some low chance pops across our north. Temps
begin to recover a bit by this time with highs more solidly into the
60s. Tuesday could begin to flirt with some 70 degree readings for
some if it trends drier.

&&

.AVIATION /06Z TAFS THROUGH 12Z THURSDAY/...
Issued at 130 AM EDT Wed Apr 17 2024

Impacts/Confidence:
- Medium confidence in isolated coverage of VCTS early this morning
as well as LLWS
- Medium to high confidence in MVFR ceilings this morning.
- High confidence in strong gusty winds today

Discussion...Current radar and satellite show isolated coverage of
storms across the forecast area. Current trends indicate that this
activity will continue to diminish as it moves to the east. As a
result, decided to leave the VCTS mention through sunrise and amend
if necessary. In addition, the presence of a decaying LLJ will
continue promoting LLWS conditions for a few more hours. As for
ceilings, an MVFR cloud layer should set in this morning in the wave
of precipitation and last until around 17Z. Otherwise, winds will
persistently gusts between 25 to 30 knots today with occasional
gusts of 30-35 knots in the afternoon. There is a conditional threat
of strong storms in the afternoon, but confidence in initiation and
coverage substantially limit predictability, so reflected dry
conditions.

Extended Outlook...Another round of storms (potentially strong) is
possible Thursday evening/night.

&&

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

&&

$$

SHORT TERM...ALL
LONG TERM...BJS
AVIATION...ALL