514
FXUS63 KLMK 222106
AFDLMK

Area Forecast Discussion
National Weather Service Louisville KY
506 PM EDT Wed May 22 2024

...Updated Mesoscale Discussion...

.KEY MESSAGES...

*   Strong/severe storms possible region wide this afternoon with
    damaging winds, hail, and very heavy rainfall being the main
    threats.

*   Stormy pattern with a risk for localized flooding Thursday
    through Tuesday with strong/severe storms possible Sunday.

&&

.MESOSCALE...
Issued at 505 PM EDT Wed May 22 2024

Widespread showers and thunderstorms are ongoing across southern KY
at this hour. Overall, have seen some fairly widespread rainfall
amounts between 1 and 2 inches, with locally higher amounts
approaching 3 inches in spots. Given that there is a bit of a
training aspect to the showers and storms, and more development
currently upstream, localized flooding is a concern going into the
evening hours. Will continue to monitor through late
afternoon/evening.

Also monitoring the threat for strong to severe storms over the next
several hours as a secondary area of storms are trying to form along
the frontal boundary currently draped across western KY up through
the Ohio River Valley. So far, these storms have struggled despite
good mid level lapse rates (> -7C/Km), moderate instability (ML CAPE
values 2000-2500 J/KG), and sufficient deep layer shear (~40 knots
or so), and good surface convergence along the front. A couple of
factors could be A wavy outflow boundary extends roughly west-east
from western KY, but dipping south a bit into the northern part of
Middle TN. Any potentially severe storms are now south of the TN
border, with cooler and more stable air at the sfc on the KY side.
13Z RAP data and SDF ACARS data reveals 1000-2000 J/kg MUCAPE above
the low-level inversion in central KY. However, given the more
stable air near the surface and the position of the outflow
boundary, the near term (through Noon-1 pm EDT) severe weather risk
is low.

Will have to watch the northern half our CWA over the next few
hours, because if storms are able to get established, then they
would likely have a higher damaging wind threat (DCAPE values around
1000 J/KG). Overall the drier lower levels combined with the
moderate instability would support some enhance microburst potential
with any stronger storm. Confidence is low in how much development
northward we will see, including SPC also being low confidence. A
conference call was recently held to discuss Watch potential, but
ultimately the worked over airmass over southern KY and lower
confidence northward were limiting factors for a Watch at this time.

&&

.SHORT TERM /THROUGH THURSDAY/...
Issued at 341 PM EDT Wed May 22 2024

Forecast is still on track to see scattered clusters of strong to
severe thunderstorms this afternoon into the evening hour. Sfc cold
front remains oriented northeast to southwest stretching from around
Ft. Wayne, IN, to around Bloomington, IN curving towards Vincennes,
IN and along the borders of far western KY and southern IL. Current
afternoon mesoanalysis shows Td mainly in the upper 60s to even a
few low 70s southern IN and most of KY. SBCAPE ranging from 1500-
3000 J/kg, with the lowest values mostly to the east/southeast where
shower/storm activity has been persistent most of the afternoon.
Visible satellite imagery shows partly to mostly clear skies along
the Ohio River into southern IN with mostly cloudy conditions across
our southern counties. Area WSR-88D continues to show a linear
cluster of showers/storms along a prefrontal boundary stretching
from the Bluegrass then southward along the KY/TN border. This
convection stretches back into far western TN. SPC continues to keep
all of central KY in a slight risk for severe storms with gusty
damaging winds being the main threat as DCAPE values along and ahead
of the sfc boundary across southern IN and along the OH River range
from 1100-800 J/Kg. Large hail can`t be ruled out given the ample
amount of instability especially seen in the hail growth zone on
model soundings for later this afternoon and evening. While the
tornado threat is relatively low, shear still looks to be between 30-
40kts. Hi-res CAMS like to lift the cluster of convection currently
over far western TN northeastward into our southern CWA later this
afternoon and evening. Feel the main focus and highest probability
of strong to severe storms will be across our southern CWA along the
KY/TN border but any outflow associated with these storms working
into the higher instability to the north and interacting with the
slow approaching sfc boundary would likely initiate additional
convection north of the Parkways towards the Ohio River with the
potential for some supercells and even linear development later this
evening. While activity continues to along the KY/TN border, our
best chance remains between 5pm EDT this evening to around 10pm EDT
with the bulk of the activity pushing out between 11pm/Midnight EDT.

While focus is on severe potential the other impact will be the
potential for heavy rain and localized flooding. PWAT axis on
mesoanalysis stretching from Memphis TN where we have a bullseye of
2.00" into the Bluegrass where we have 1.60" is where we are seeing
the main focus of activity so far this afternoon. Any storms will
produce very heavy rainfall and if storms train over an area
localized flash flooding is a possibility. The one positive here is
that the dry weather the last couple of day has allowed current 1hr
FFG to range from around 1.75" at the lowest to as high as 3.00"
over our CWA.

Once activity pushes off and out of the area overnight we will be in
a bit of a lull but a second shortwave pulse will work across the
Ohio Valley overnight into tomorrow morning. This could produce
another cluster of showers and storms working from the Bootheel of
MO through KY and southern IN during the morning hours.  Sfc
boundary looks to stall out over the Ohio River for tomorrow with
more scattered showers/storms possible especially during the
afternoon. It`s possible we could see a lull in the activity briefly
during late morning into early afternoon. The threat of severe
appears to be lower but remains as SPC has the southern half of our
CWA in a marginal risk (1 out of 5) for the potential for strong to
severe storms.

&&

.LONG TERM /THURSDAY NIGHT THROUGH WEDNESDAY/...
Issued at 400 PM EDT Wed May 22 2024

Looking into the long-term, temperatures this coming week will be
fairly seasonal with highs on Friday up to 5 degrees or so above
normal. These slightly warmer than normal temperatures from a mix of
sunshine and warm air advection will be replaced by slightly cooler
than normal temperatures on Tuesday and Wednesday. This will be
possible as a cold front on Monday moves through the Lower Ohio
Valley which will help stop warm air advection and will begin
dropping dew points into the 50s from the 60s. Precipitable water
values will also drop to around an inch or below. Surface high
pressure, centered to the west, should help to produce mostly sunny
skies with high temperatures 5 degrees or so below normal.

But before this cold front pushes through and clears the area, a
series of warm and cold front moving over and around southern
Indiana and central Kentucky will provide chances for showers and
thunderstorms on Friday and Saturday. During most of this time,
precipitable water values will vary between 1.3-1.6". Just ahead of
a front, these values could reach up to 2". Model soundings and
hodographs look like your typical summer day. They have plenty of
instability but lack shear. This will limit the type of expected
severe weather. We could see heavy rain in isolated areas which
could cause some limited flooding issues and gusty winds.

Sunday is worth keeping an eye on. It`s still a ways out, so the
details will come into better focus, but the region will be under
the exit region of an upper jet streak with backing winds towards
the surface. This will produce deep layer shear for the
continued continuedinstability which will help severe weather
to become more organized. Hodographs currently look favorable
for tornadoes, so all severe weather types are on the table.

&&

.AVIATION /12Z TAFS THROUGH 18Z THURSDAY/...
Issued at 1259 PM EDT Wed May 22 2024

Active weather expected in the near term with multiple rounds of
showers and storms likely to impact most TAF sites today. Most
shower and storm activity is south of a line from Madison County
(KY) to Simpson County (KY) and is gradually pushing east.
Additional showers and storms will develop to the west and southwest
later today and move into the region. Some of this activity will
likely clip TAF sites and result in briefly reduced cigs/vis.

We should see a lull in activity overnight, but more showers and
storms could develop toward dawn tomorrow and overspread much of the
region.

&&

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

&&

$$

MESOSCALE...BJS
SHORT TERM...BTN
LONG TERM...KDW
AVIATION...DM