203
FXUS63 KLMK 211042
AFDLMK

Area Forecast Discussion
National Weather Service Louisville KY
642 AM EDT Tue May 21 2024

...Updated Aviation Discussion...

.KEY MESSAGES...

*   Dry weather and above normal temperatures continue today.

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

*   Strong to severe storms possible Wednesday afternoon into
    Wednesday night, with an increased risk for localized flooding
    Thursday through Monday.

&&

.SHORT TERM /THROUGH TONIGHT/...
Issued at 300 AM EDT Tue May 21 2024

Overnight satellite imagery shows a bit of mid-high level cloud
cover pushing through the region this morning.  Area radars were
devoid of echoes and temperatures ranged from the lower 60s in the
valley locations to the mid-upper 60s on the ridges.  The local warm
spot was down in the Bowling Green area where temperatures were in
the lower 70s.  For the remainder of the overnight period, no
significant weather is expected.

For today, we expect a similar weather day across the region.  A mid-
level ridge axis will push east of thee area and the pressure
gradient will tighten up a bit.  Our surface winds will veer from
the south-southeast to the southwest and become gusty from the late
morning through the afternoon hours.  We`ll see another diurnally
driven cumulus field develop.  The latest guidance is a bit drier
than in the last several runs as the models are resolving the poor
mid-level lapse rates across the region.  It is still is possible
that a few renegade showers/storms could develop this afternoon.  If
so, the most probable area would be over in the Bluegrass region and
the probability of coverage would be 10 percent or less.  High
temperatures will be in the mid-upper 80s.

For tonight, winds will diminish toward sunset.  Widespread
convection should be in progress across the MO Valley into the
Midwest with a significant outbreak of severe weather likely over
the upper Midwest.  Most convective allowing guidance shows a line
of showers/storms pushing across eastern MO/IL and eventually into
IN/KY a few hours after midnight.  This convection will initially be
rooted in the surface layer, but as it moves into our region late
tonight, it will become increasingly elevated and will be moving
into an environment that is more hostile for sustaining it.  With
that said, a few showers and storms will get into our region late
tonight with the best chances in areas along and west of I-65. Lows
overnight will be in the upper 60s to around 70.

&&

.LONG TERM /WEDNESDAY THROUGH MONDAY/...
Issued at 300 AM EDT Tue May 21 2024

Wednesday through Wednesday Night...

A vertically stacked low pressure system will be centered over the
northern Great Lakes on Wednesday morning. This system will send a
line of storms through the Midwest and into the Ohio River Valley.
By Wednesday morning, this line will weaken while moving through the
region. The line will have outrun the best instability and dynamics,
therefore, dissipating over the Ohio Valley. A moist airmass with
low 60s dew points and PWATs around 1.5 inches, could lead to heavy
downpours and gusty winds with stronger storms.

Guidance trends continue to suggest atmospheric recovery for
convective initiation potential along the approaching cold front by
Wednesday afternoon and lasting into the overnight hours.
Destabilization will bring SBCAPE values into the 1000-1500J/kg
range. 40% of LREF and NBM ensembles exceed 1500J/kg. Low-level
lapse rates will slowly increase, while mid-level lapse rates will
be in the 7-7.5 C/km range over the northern third of the region.
90% of ensembles agree on at least 25-30kts of sufficient, but
marginal deep-layer shear. Moderate moisture advection into the
region will bring surface dew points into the mid 60s and PWATs
around 1.75 inches. These conditions could lead to heavy
downbursts/wet microbursts, damaging winds and marginal hail.

Greatest threat area is over the northwestern half of the region,
which is primarily along the parkways and northwest. Storms may
initiate along the Ohio River and move ENE as the front pushes into
the region. Areas in the SE half of the region are forecasted to see
0.25-0.5 inches of rain, where the NW half of the region is
forecasted to see 0.5-1.0 inches of rain, with locally higher
amounts possible.

Thursday through Monday...

The cold front will likely stall over the Ohio Valley, and coupled
with multiple shortwave systems and continued southwesterly flow,
will lead to increased chances for showers and storms through
Monday. 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 Monday.

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.

Given multiple days of rain and possible training of cells, flooding
and flash flooding is possible. Current QPF for this timeframe is
2.5-3.5 inches, with locally higher amounts possible.

&&

.AVIATION /06Z TAFS THROUGH 12Z WEDNESDAY/...
Issued at 641 AM EDT Tue May 21 2024

VFR conditions are expected through the upcoming TAF period.
Scattered to broken deck of Cu will be possible through the period
with bases around FL050.  Winds will pick up out of the southwest
with speeds of 8-10kts and gusts of 15-21kts at times during the
afternoon hours as the pressure gradient tightens up.  Winds are
expected to diminish toward sunset.  Late in the period, a line of
convection will move into the region from the west.  Showers and a
few storms will be possible after 22/06Z.  These storms will outrun
the instability gradient and weaken as they cross the region.  KHNB
may see some thunder out of this and will include a mention of VCTS
late tonight.

&&

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

&&

$$

SHORT TERM...MJ
LONG TERM....SRM
AVIATION.....MJ