305
FXUS63 KLMK 082251
AFDLMK

Area Forecast Discussion
National Weather Service Louisville KY
651 PM EDT Wed May 8 2024

.KEY MESSAGES...

*   Scattered severe storms possible this evening. All severe
    hazards will be possible.

*   Flooding concerns increasing for southern and central Kentucky.
    A Flood Watch is in effect through Thursday morning.

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

&&

.UPDATE...
Issued at 650 PM EDT Wed May 8 2024

Strong convection has moved into the region from the southwest along
a warm front situated over western Kentucky and central Tennessee.
Instability over the BWG area is around 3000 J/kg of SBCAPE and
decreases quickly to the northwest. Therefore, storms are weakening
as they move to the northwest and away from the best forcing and
instability. Have decided to add in Casey, Lincoln, Marion, and
Boyle counties into the tornado watch. As storms travel over these
counties they have been maintaining healthy structure, although not
as strong as other storms to the southwest.

Hodographs above about 1km show nearly unidirectional winds which is
supporting splitting cells. Left moving splits are showing higher
hail potential with some reports of golf ball sized hail. Right
moving splits have a higher potential for tornadoes. The right
movers so far have been impacted by merging cells, have larger hail
content, and have not developed strong circulations. If a storm does
veer to the right, it will have the potential to ingest better low-
level SRH values (which are currently around 200-250 m2/s2).

The greatest threat for severe storms will be to the south of a line
extending from Hardinsburg through Bardstown.

Flooding and flash flooding is a threat through the overnight hours
given individual cells leading to downpours and multiple cells
entraining over an area. With sunset occurring in the next few
hours, travelers are advised to use caution. Flooding at night is
very difficult to see.

&&

.SHORT TERM /THROUGH THURSDAY/...
Issued at 337 PM EDT Wed May 8 2024

=====================
This afternoon and evening
=====================

A MCV is located near St. Louis this afternoon, evolving slowly
eastward. An effective warm front/remnant outflow boundary extends
SE through portions of western and southern KY, with sfc dewpoints
near 70 F along and south of the boundary. Scattered thunderstorms
have developed in south-central KY along the boundary and associated
instability gradient. Portions of south-central KY have been the
slowest to destabilize in the wake of morning convection and cloud
debris. Sfc temperatures are only now warming into the lower 70s at
BWG, with mid/upper 70s to near 80 noted across southern IN and the
northern half of KY. Likely still have a shallow low-level inversion
present across south-central KY, where ongoing impressive
supercellular storms could be elevated. However, this is also along
a boundary/instability gradient which continues to drift northeast
with time. A long, straight hodograph above 1 km is also supporting
splitting supercells which we have already seen with a left-mover
tracking northeast through Ohio County and a right-mover now moving
east across Warren County. Storms that move further to the right (E,
ESE) will realize greater low-level SRH and have a better chance of
producing a tornado.

A Tornado Watch has been issued for portions of central and southern
KY where the near-term tornado risk is highest - roughly southwest
of a line from Brandenburg to Campbellsville. Further north and
northeast, low-level winds are notably weaker and the tornado risk
is lower.

The scattered storm activity ongoing now is expected to continue to
drift east and northeast with time, while increasing in coverage
this evening. So while severe weather is still very much possible
further north, such as along the I-64 corridor, the window for
storms and severe weather is shorter. The most likely time frame for
severe weather is now (3-4 PM) through Midnight. But areas further
northeast, such as from Louisville to Lexington, have the best
chance at seeing a severe storm from 5-11 PM EDT.

Given the destabilizing airmass (1000-2000+ J/kg MLCAPE) and very
strong effective deep layer shear (50-60 kt), supercellular storm
modes are likely well into the evening hours. Increasingly larger
clusters and perhaps bowing segments will be possible beyond 8 PM.
All severe hazards remain possible through the evening hours, with
the highest risk in the Tornado Watch area (this includes large
hail, damaging winds of 70+ mph, and tornadoes.

A Flood Watch also remains in effect for much of the area. Again,
the highest risk for flash flooding is concentrated across the
southwestern half of the CWA where the greatest thunderstorm
coverage is anticipated. Will need to watch closely for any training
along the boundary as it slowly lifts northeast. PW values are also
highest, exceeding 1.5 inches, along the lingering boundary. 1-3
inches of rain will be possible, with the highest amounts across
south-central KY. Localized higher totals of 3+ inches cannot be
ruled out across south-central KY.

=====================
Tonight and tomorrow
=====================

A final band of showers and storms will likely push southeast across
the region late this evening into tonight ahead of the cold front.
Confidence in severe weather after Midnight is much lower, but
localized damaging winds cannot be ruled out. Waning instability
will help to limit the wind threat at ground level. This activity
will likely weaken with time as it exits from NW to SE by the early
morning hours. Thursday looks drier with morning lows in the 60s and
afternoon highs near 80 F.

&&

.LONG TERM /THURSDAY NIGHT THROUGH WEDNESDAY/...
Issued at 337 PM EDT Wed May 8 2024

By Thursday evening, the cold front responsible for recent inclement
weather will be off to our east along with most, if not all,
convective activity. Aloft, a positively tilted longwave trough will
extend from the NE US to an upper low positioned over the Four
Corners region of the SW CONUS. Embedded shortwave energy will
propagate through the longwave pattern into the OH Valley during the
day Friday, coupled with wrap-around moisture from the departing
surface low, and resulting in lingering precip chances. GFS
soundings suggest fog/stratus potential Friday morning; furthermore,
12Z NAM3k and HRRR soundings also show a saturated layer from just
above the surface to around 800/750mb, indicative of the possibility
of drizzle across southern Indiana and north central KY until late
Friday morning.

With the upper trough positioned over the OH Valley, temperatures
through the weekend will be several degrees below normal, resulting
in more of a Springtime feel: looking for daily highs in the upper
60s to low 70s through the weekend. Another shortwave will makes its
way through OH Valley Saturday, bringing another chance of light
showers as well as tightening the pressure gradient enough to
produce some breezy conditions, with gusts expected in the 20-25 mph
range Saturday afternoon. Low level ridging will simultaneously
begin building into our region Saturday, which would suggest dry
conditions for Sunday.

Low amplitude upper level ridging will pass overhead to start the
workweek, as the low level high center passes to our east. This
leaves our region on the dirty side of the high with return flow and
an uptick in low level moisture. Rain and storm chances return as
early as Monday evening through Mid week. Not expecting a washout,
but long range models` low temporal resolution have yet to resolve
finer details. It`s worth repeating though that CIPS/CSU/SPC severe
comparisons show no signs of severe weather during this timeframe.

&&

.AVIATION /18Z TAFS THROUGH 00Z FRIDAY/...
Issued at 149 PM EDT Wed May 8 2024

Scattered TSRA developing this afternoon along an outflow boundary
extending from southern IL and western KY southeast along the KY/TN
border. This boundary will slowly drift northeast with time, making
for a complicated forecast for BWG this evening. Thunderstorms will
likely impact that terminal at times, lowering both ceilings and
visibilities significantly for relatively short periods of time.

Additional SCT TSRA possible later this evening, especially after
21Z, for the I-64 corridor from HNB east. But areas further
northeast, such as LEX, will see a bit less activity/shorter
duration of TSRA before activity clears us to the south by 03-06Z
Thu.

For this evening, any thunderstorms in the vicinity of any of our
terminals could become severe quickly and pose a risk for large
hail, damaging winds, and torrential rainfall.

&&

.LMK WATCHES/WARNINGS/ADVISORIES...
KY...Flood Watch through Thursday morning for KYZ023>043-045>049-
     053>057-061>067-070>078-081-082.
IN...Flood Watch through Thursday morning for INZ077>079-084-
     089>092.

&&

$$

UPDATE...SRM
SHORT TERM...EBW
LONG TERM...CRG
AVIATION...EBW