358
FXUS63 KLMK 260754
AFDLMK

Area Forecast Discussion
National Weather Service Louisville KY
354 AM EDT Sun May 26 2024

.KEY MESSAGES...

*   Multiple waves of strong to severe storms possible today and
    tonight. Widespread damaging winds are possible, and tornadoes
    and large hail cannot be ruled out.

*   Repeated heavy rainfall could result in flash flooding,
    especially over south-central Kentucky.

*   The greatest risk for severe weather and flooding will be after
    dark. Have multiple ways to receive warnings, and be aware of
    the dangers of nighttime flooding.

&&

.SHORT TERM /THROUGH THIS AFTERNOON/...
Issued at 353 AM EDT Sun May 26 2024

Multiple opportunities for severe weather over the next 24 hrs, with
the impacts of each impulse dependent on the one before it. Because
of that interdependence, confidence in the severe threat is limited.
However, with multiple waves of storms to bring copious rainfall,
confidence is increasing in a flash flood threat, especially over
south-central Kentucky.

The general idea remains the same with at least two, perhaps three
waves of storms. First wave will be a warm advection wing, currently
reflected by convection over the Ozarks, and will be pushing
eastward across Kentucky during the morning hours. Look for that to
arrive in south central Kentucky by mid-morning, but likely in a
weakened state.  Could see some rejuvenation as it makes its way
into an increasingly unstable environment toward midday, which would
support a damaging wind threat. Tornado threat will remain low  in
the early part of the day as the shear isn`t that strong yet.

Perhaps the biggest question mark in the process is a MCV, which we
expect to develop from the activity currently over NE Kansas, and
how closely it will follow the initial wave of storms. This impulse
could provide another opportunity for strong convection in the
afternoon, if it isn`t moving into an already overturned atmosphere.

The third impulse is the one that prompts the most confidence, and
is expected to initiate convection shortly before sunset over
southern Illinois. By this time low-level and deep-layer shear will
be much more favorable, and the environment will be moderately
unstable after a few hours of late afternoon heating. Expect this
convection to grow upscale into a large squall line caprable of
producing widespread damaging winds as it pushes ESE across southern
Indiana and central Kentucky. A few segments could become oriented
perpendicular to the shear vector, leading to mesovortex development
and at least some tornado risk, but it will be limited by higher
than ideal LCLs. Potential limiting factor in the wind threat is the
timing, especially as the line pushes south and east after dark,
with increasing chances for a low-level inversion to keep momentum
from mixing down. All severe threats are still on the table.

Flash flooding is an additional threat, and confidence is increasing
that we will see at least a few locations that pick up excessive
rainfall with a potential three separate waves of convection. Threat
is the greatest across south central Kentucky, where recent heavy
rains have lowered Flash Flood Guidance, and the late-night squall
line will be most prone to hang up, potentially resulting in
training storms. That area is now highlighted by WPC in a Moderate
Risk for excessive rainfall, with the rest of Kentucky and southern
Indiana in a Slight Risk. Didn`t want to slice things too fine, so
we have hoisted a Flood Watch for the entire CWA, from 12Z today
through 12Z Monday. The greatest threat will be with the final round
of storms tonight.

&&

.LONG TERM /TONIGHT THROUGH SATURDAY/...
Issued at 353 AM EDT Sun May 26 2024

Monday through Tuesday Night...

Deep low pressure is forecast to reach Lower MI by 12Z Monday, with
a trailing cold front advancing through central IN and western KY. A
trailing upper level shortwave trough will swing across the Ohio
Valley Monday morning as the cold front moves through the region.
This could touch off a few weak showers and storms early in the day,
though most will see a dry start to the day in the wake of severe
storms late Sunday.

There is a slightly greater chance (30%) for showers and storms in
the Bluegrass/Lake Cumberland regions in the afternoon. Slightly
richer moisture and a bit more time for the airmass to destabilize
prior to fropa results in the slightly higher rain chances. However,
precip will be sparse overall. Expect a mostly cloudy start to the
day, with lower clouds thinning during the second half of the day.
It will be breezy with gusts of 20-30 mph. Highs will range from the
mid 70s to around 80 F.

Notable upper level troughing lingers over the Great Lakes and Upper
Midwest through Tuesday night, keeping deeper moisture bottled up to
our north. An amplifying upper level ridge builds from the Rockies
to the Plains as sfc high pressure strengthens over the northern and
central Plains. Largely dry weather is expected with lows in the 50s
and afternoon highs in the mid 70s to near 80 F.

Wednesday through Saturday...

Ridging builds east across the MS and OH Valleys through late week,
resulting in a stretch of pleasant weather. Highs will be in the 70s
Wednesday and Thursday with comfortable humidity levels. Morning
lows will generally be in the 50s, though some spots will see
readings in the 40s Thursday and Friday mornings. Temperatures will
warm back to around 80 degrees Friday afternoon.

A highly meridional flow pattern will be in place heading into next
weekend. Ridging slowly drifts to the east as a Plains low pressure
system moves toward the region. Rain returns to the forecast for
late Saturday or Sunday, though timing remains uncertain.

&&

.AVIATION /06Z TAFS THROUGH 12Z MONDAY/...
Issued at 131 AM EDT Sun May 26 2024

Impacts/Confidence:

- High confidence in two or more waves of thunderstorms with heavy
rain and gusty winds Sunday afternoon and evening, medium confidence
in specific timing.

- Medium to high confidence in gusty southerly winds Sunday afternoon

Discussion... Sfc boundary draped near the Ohio River, with light
easterly winds to the north and some moisture pooling just to the
south. Front will begin to lift northward as a warm front overnight,
with some concern about fog toward morning, mainly at LEX. However,
with cloud cover, and the boundary layer trying to mix a bit before
sunrise, not confident enough to include any vis restrictions at
this time.

By late morning, the first of at least two waves of showers and
storms will push across the area from west to east. This convection
will be in a weakening state, so impacts will be mostly limited. Did
include a PROB30 for IFR vis in the heaviest precipitation.

Once the first impulse moves through, winds will increase out of the
south with gusts near 20 kt through the afternoon.  Could see
another wave of showers and storms in the mid-late afternoon, but
not sure there is enough opportunity to destabilize.

Either way, expect a break from roughly 21Z until 01-02Z, after
which a line of gusty, possibly severe storms moves across the
terminals ahead of the incoming cold front. Covered this activity
with VCTS for LEX and BWG, but since it will most likely reach SDF
first, did include a wind shift with gusts to 30 kt, and IFR vis
with the TS/CB mention in the late evening.

This will continue to be massaged in later TAF issuances. Suffice to
say there will be intervals of stormy weather, but with periods of
dry/benign weather and VFR conditions in between.

&&

.LMK WATCHES/WARNINGS/ADVISORIES...
KY...Flood Watch from 8 AM EDT /7 AM CDT/ this morning through
     Monday morning for KYZ023>043-045>049-053>057-061>067-
     070>078-081-082.
IN...Flood Watch from 8 AM EDT /7 AM CDT/ this morning through
     Monday morning for INZ076>079-083-084-089>092.

&&

$$

SHORT TERM...RAS
LONG TERM...EBW
AVIATION...RAS