365
FXUS63 KLMK 080708
AFDLMK

Area Forecast Discussion
National Weather Service Louisville KY
308 AM EDT Wed May 8 2024

.KEY MESSAGES...

*   Potential for multiple rounds of strong to severe storms today
    and tonight. All severe hazards will be possible.

*   Flooding concerns increasing southern and central Kentucky. A
    flood watch is in effect through Thursday morning.

*   Below normal temperatures return by Friday and persist into
    the weekend.

&&

.SHORT TERM /THROUGH TONIGHT/...
Issued at 305 AM EDT Wed May 8 2024

=====================
This morning
=====================

Broken line of showers and storms ahead of a frontal boundary
continues to push southward this morning across the region.
Environment ahead of these storms does feature good shear and
instability, but poor mid-level lapse rates have made many of the
storms struggle to maintain any sort of strength or severity, and
outflow boundaries have begun racing ahead of most convection. That
being said, there is still some low-end potential that they could
produce a quick spin-up tornado should everything come together just
right... and after coordination with SPC, a new watch has gone into
effect to cover our western-most counties ahead of the line where
the best chance for a quick spin up exists.

These showers and storms should continue sinking southward this
morning but will stall with their outflow boundary near or south of
the TN border after dawn. Where exactly this occurs will be crucial
for how the rest of the day evolves.

=====================
This afternoon
=====================

The 00z guidance has some subtle differences on how the outflow
boundary and storm initiation along it evolve through the day, but
most point to the boundary lifting slightly northward across the
western part of Kentucky by late morning into the afternoon hours.
Environment on the warm side of the boundary will be very ripe for
severe storms as high amounts of shear and instability aid in
sustaining organized convection, so any convection that develops in
the warm sector would be capable of all severe hazards. Convection
that crosses into the boundary or even just slightly into the `cool`
side of the boundary would also need to be watched closely, as low
level helicity would likely be enhanced near this area and would aid
in low level mesocyclogenesis for tornado potential (in addition to
hail/wind threats).

If this boundary ends up being a bit farther south than anticipated,
our severe threat for the afternoon will be much lower than
expected.

What could end up being a bigger issue today is the flood threat.
Storm motions will be nearly parallel to the west-east orientation
of the boundary to support a setup of training storms. With deep
moisture and high PWATs in place, as well as already saturated soils
from rounds of rain earlier this week, flooding will likely become
an issue across portions of central/southern Kentucky. A flood watch
is now in effect through Thursday morning to cover this threat.

=====================
Tonight
=====================

An approaching cold front from the west will likely bring a large
line of convection into the region overnight. The severity of it for
our region will be highly dependent on how far north the
aforementioned boundary near the KY/TN border lifts. At this time,
the most likely part of our region to see impacts from this line
would be southern Kentucky. All severe hazards would be possible.
Additionally, flooding issues would only be exacerbated by this
line as it moves through the region.

All of this activity should push east of the region by sunrise
Thursday morning.

&&

.LONG TERM /THURSDAY THROUGH TUESDAY/...
Issued at 130 PM EDT Tue May 7 2024

*** IMPORTANT: THIS SECTION IS OUT OF DATE AND WILL BE UPDATED
 HERE SHORTLY ***


==== Local Flooding Possible Wednesday Night ====

Moderate to high confidence remains for a significant regional
severe weather event Wednesday afternoon into Wednesday night for
parts of the Ohio and Tennessee Valleys.

Synopsis: Closed upper low centered over the northern Plains
Wednesday morning will gradually work eastward towards the Upper
Mississippi Valley during the day as a weak shortwave ridge builds
over the Ohio Valley. At the surface, a quasi-stationary boundary
will be located just along the Ohio River as an elongated area of
sfc low pressure over the central plains slowly works towards
central IN by Thursday morning. As the sfc low works towards the
Ohio Valley, the stalled boundary will become a warm front with dew
points south of the boundary over southern IN and central KY in the
mid/upper 60s to even a few areas to the south near 70. As
temperatures warm into the low/mid 80s during the afternoon, the
atmosphere will quickly destabilize with SCAPE values ranging
between 1500-3000 J/kg. HREF ensemble soundings indicate 0-6km bulk
shear > 50 kt.

The main challenge will be timing and placement of initial
convection during the day Wednesday. While the setup for a
significant severe weather threat continues over the Ohio Valley as
indicated by the SPC enhanced outlook (3/5) over our entire county
warning area, there are a few elements that could potentially impact
the overall severe threat during the day Wednesday.

Hi-res models are in agreement of remnant boundaries associated with
Tuesday nights storms to be located across central TN Wednesday
morning. This boundary looks to be the focal point for convection
initiation during the day Wednesday. Timing and location of
convective activity Wednesday morning into the early afternoon could
play a large role in just how strong storms get later in the
afternoon and evening over central KY and southern IN. Some of the
hi-res convective allowing models want to develop convection over
far western KY while others start to develop activity over MO
Wednesday morning. Any cloud cover and potential outflow from this
activity arriving early in the day before maximum heating would
likely limit storm severity towards the afternoon. Another limiting
factor with early convection to our south and southwest early
Wednesday would be to limit the LLJ which is indicated by the 00z
HRRR and to some extent the NAM3K. Finally, placement of the stalled
boundary and its northern progression allowing for the CWA to be in
the deep warm moist sector behind increasing instability over the
area. A lot of the above mentioned factors will be determined by how
the storms Tuesday into Tuesday night unfold over the area. With all
that being said, all threats are still possible Wednesday afternoon
with initial cellular development before becoming more of a QLCS
ahead of an approaching cold front Wednesday night into Thursday
morning.

Tornado threat: Model sounding continue to indicate low-level
curvature on hodographs showing the potential for plenty of
streamwise vorticity ingestion by storms, with some eSTP values for
tornadoes >=EF2 Wednesday afternoon.

Hail threat: With forecast soundings showing large CAPE in the -10
to -30C hail growth zone. Strong deep layer shear and steep mid
level lapse rates keep large hail a possibility.

Wind threat: While we may not have a strong LLJ to work with, high
PWAT values leading to precipitation loading along with steep low-
level lapse rates increase the threat of strong damaging wind gusts.

Flash Flood threat: With PWAT values above 1.50" and numerous
clusters of storms Wednesday afternoon along with a line of storms
Wednesday night into Thursday moving through the area. Add to that
already wet ground from rains over the last couple of days will
increase the threat and concerned for localized flash flooding.
Especially in areas south of the Kentucky parkways that will see
heavy rain on Tuesday then again on Wednesday.

With the above mentioned limiting factors, confidence is higher for
linear severe storms associated with the approaching cold front than
the development of supercells during the afternoon and early evening
on Wednesday.

**Like any forecast, there are sources for potential bust. Any
convection that might get going Wednesday morning could decrease
instability for afternoon redevelopment, as would cloudiness being
more widespread, or stronger capping in our position well within the
warm sector. While a significant severe weather event is still a
possibility, this isn`t a done deal. Stay tuned to the latest
forecast information between now and Wednesday afternoon to keep
abreast of changes.**

Thursday - Monday:

Amplified pattern develops Thursday through the remainder of the
forecast period with a large ridge building to the west and deep
trough across the eastern US. This will keep occasional
shower/storms chances in the forecast thanks to a series of
shortwave disturbances moving through the northwest flow aloft.
Temperatures during this period will be below normal for early May
with highs in the 70s and even 60s on Friday.

&&

.AVIATION /06Z TAFS THROUGH 12Z THURSDAY/...
Issued at 1258 AM EDT Wed May 8 2024

A broken line of showers and storms continues across southern
Indiana, southern Illinois, and western Kentucky this morning ahead
of a cold front. This activity should gradually push southward as
the cold front slowly sags into Kentucky, but eventually stall out
across southern Kentucky later this morning. How this boundary
evolves later in the day will be crucial to storm chances at TAF
sites, and at this current time, the BWG terminal will likely
experience several rounds of showers/storms leading to poor flying
conditions today.

Late this afternoon into the overnight hours, one or multiple lines
of storms are expected to push through the region ahead of a cold
front and will impact all TAF sites.

Outside of storms, VFR conditions are expected for most of the
forecast period.

&&

.LMK WATCHES/WARNINGS/ADVISORIES...
KY...Flood Watch through Thursday morning for KYZ023>030-034>043-
     045>049-053>057-061>067-070>078-081-082.
IN...Flood Watch through Thursday morning for INZ090.

&&

$$

SHORT TERM...DM
LONG TERM...BTN
AVIATION...DM