606
FXUS63 KLMK 212359
AFDLMK

Area Forecast Discussion
National Weather Service Louisville KY
759 PM EDT Tue May 21 2024

...Updated Aviation Discussion...

.KEY MESSAGES...

*   Unsettled weather returns Wednesday, with on and off chances for
    showers and storms through the weekend.

*   Isolated severe storms possible Wednesday afternoon into
    Wednesday night.

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

&&

.SHORT TERM /THROUGH WEDNESDAY NIGHT/...
Issued at 257 PM EDT Tue May 21 2024

An upper level shortwave trough and deepening sfc low are lifting
northeast across the central Plains this afternoon, with downstream
ridging across much of the eastern US. Southerly low-level flow is
beginning to increase in the Ohio Valley downstream of the low
pressure system, but the primary low-level jet/moisture transport
axis will remain off to our north and west through this evening.
Strong heating of a fairly moist airmass (sfc dewpoints are
currently mid/upper 60s) has led to MLCAPE creeping past 1500 J/kg.
Despite a lack of notable mesoscale forcing, we are eclipsing
convective temperatures in northern KY where scattered showers and a
few storms are drifting northeast toward Covington. While it`s
close, still do not think we`ll see a whole lot this afternoon in
central KY and southern IN. A few showers/storms cannot be ruled
out, but cu development is tempered by a lack of mechanical forcing
and warm air in the mid-levels (as seen on recent SDF ACARS
soundings). Rest of the day looks quite warm and somewhat humid with
max temps in the 85-90 F range.

The first half of tonight looks warm and dry. A band of showers and
storms is forecast to sink southeast through Illinois and Missouri,
weakening as pushes further east of the Mississippi. These storms
will outrun the instability axis, and deep-layer will be weak also.
Expect weakening showers and isolated embedded storms to push
southeast across portions of southern IN and central KY between 3-10
AM EDT before diminishing altogether.

A lull with mostly dry conditions then looks likely from mid-morning
Wednesday through early afternoon. Some partial clearing should
allow for decent sfc heating and destabilization of a moist boundary
layer. HREF mean SBCAPE increases to 1500-2000+ J/kg by mid-
afternoon as a weak sfc cold front begins to stall from IN southwest
through southern IL. The upper level shortwave trough makes its
closest approach over the Midwest Wednesday afternoon and evening,
helping to steepen 3-6 km lapse rates to near 7 C/km. A slightly
more subtle convectively enhanced mid-level disturbance will likely
lift ENE from the Ozarks across TN, which should help boost
convective coverage first across south-central KY late Wednesday
afternoon and through the evening hours.

Overall, isolated to widely scattered storms look possible beginning
late Wednesday afternoon. The better chance of seeing storms will be
Wednesday evening and overnight. Shower/storm coverage will increase
during the evening both as the Ozarks mid-level wave approaches from
the WSW and the weak sfc boundary to the north sinks just a bit
further south into southern IN. An isolated severe storm does look
possible, mainly between 3-11 PM EDT. In addition to sufficient
buoyancy, some mid-level dry air and steep low-level lapse rates
will contribute to elevated DCAPE. This should result in isolated
strong downdrafts capable of localized damaging winds. Locally heavy
rainfall, lightning, and small hail are also likely. Large or
damaging hail seems unlikely due to marginal deep-layer shear on the
order of 30 kt. This will keep thunderstorm updrafts only loosely
organized. Brief pulses will likely produce some small hail, though.
Limited coverage through early to mid-afternoon will help keep the
flooding risk low during the daytime. Increased coverage of showers
and storms Wednesday night will boost the potential for cell
training over similar areas, and thus increase the risk for
localized flooding.

Highs Wednesday will likely be in the low to mid 80s in most areas.
Lows Wednesday night will be in the 60s.

&&

.LONG TERM /THURSDAY THROUGH TUESDAY/...
Issued at 257 PM EDT Tue May 21 2024

Thursday through Tuesday...

A cold front will likely stall over the Ohio Valley, and coupled
with multiple shortwave troughs of low pressures and continued
southwesterly jetstream flow, will lead to increased chances for
showers and storms through Tuesday. Temperatures will warm each day
from near normal to above normal. Dew points will also remain in the
mid-upper 60s, which will lead to warm and muggy conditions through
Tuesday.

Strong to severe storms are possible, however, this will likely be
determined on a day-by-day basis to assess mesoscale evolution and
recovery for convective initiation. Moisture is present through the
weekend and instability recovery looks possible each day, however,
shear remains weak-marginal.  The best day (while it`s early) looks
to be Sunday.  Model forecast soundings show instability and good
shear that could lead to strong to severe thunderstorms as a low
pressure system moves up the Ohio Valley.

Given multiple days of rain and possible training of cells, flooding
and flash flooding is possible. Current QPF for this timeframe is 2
to 4 inches, with locally higher amounts possible in the strongest
thunderstorms
.

&&

.AVIATION /00Z TAFS THROUGH 06Z THURSDAY/...
Issued at 758 PM EDT Tue May 21 2024

Tonight, a broken line of showers and thunderstorms is expected to
approach the region from the west ahead of a surface cold front. Any
precipitation with this line is not expected to enter the area until
after 06Z, with HNB being the first site to see increased chances
for rain and/or storms. Model guidance continues to show the line of
storms weakening as it moves into the region, and confidence is
decreasing that showers and storms will remain strong enough to
cause significant impacts to operations. As a result, have trended
later with MVFR CIGs at HNB and have removed TS mention during the
morning hours for now, although this may need to be added if storms
hold together. Additionally, a 35-40 kt jet around 2 kft AGL is
expected to move across the area after midnight tonight, with
marginal LLWS possible between 05-11Z.

With the front still west of the area tomorrow morning, winds will
pick up again out of the SW, with gusts of around 20 kt possible
after 13-14Z. Precipitation chances will subside during the late
morning and early afternoon hours, with latest model guidance
showing another wave of showers and thunderstorms developing around
20-21Z tomorrow. Will use PROB30 to handle these storms for now,
with additional refinements to timing and impacts likely needed in
subsequent forecasts.

Outside of storms, MVFR ceilings will be possible at HNB and SDF
late tomorrow morning as a narrow strip of low-level moisture along
the front moves overhead. Ceilings should gradually improve during
the afternoon with the help of daytime heating.

&&

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

&&

$$

SHORT TERM...EBW
LONG TERM...MCK
AVIATION...CSG