974
FXUS63 KLMK 261914
AFDLMK

Area Forecast Discussion
National Weather Service Louisville KY
314 PM EDT Wed Jun 26 2024

.KEY MESSAGES...

*   Showers and storms across the region late this afternoon and
    evening. Some storms may be strong to marginally severe with
    damaging gusty winds, small hail, frequent lightning and heavy
    rain as the main hazards.

*   Shower and storm chances return Saturday through early Sunday.
    Locally heavy rain and gusty winds will be the main threats.
    Above normal temperatures return by early/mid next week.

&&

.SHORT TERM /THROUGH THURSDAY/...
Issued at 314 PM EDT Wed Jun 26 2024

Synopsis...Small-amplitude, mid-level shortwave trough continues
moving along the Great Lakes today as it pushes a frontal wave
southward across the Ohio Valley. Meanwhile, a convectively-
generated vorticity maximum is analyzed over the Mid Mississippi
Valley with the potential to spawn another afternoon MCV once strong
convection gets established. As a result, showers and storms are
still anticipated late this afternoon and evening.  Then, a pattern
change is anticipated tonight and tomorrow as a mid-level ridge
starts building from the south signaling the arrival of dry weather.

This Afternoon and Evening...Complex mesoscale environment
developing this afternoon given the southward-sagging cold front
across central IN and evolution of potential MCV farther upstream
over eastern Missouri. Current radar coverage indicates isolated
convective initiation along south-central KY ahead of the favorable
convergent branch of the MCV where substantial warm air advection
normally occurs. Another area of convective initiation would be
north of the Ohio River, as some CAM models have indicated, based on
the position of the moisture convergence ahead of the front and
recent clearing trend was observed in visible satellite channel. It
is important to notice that models have struggle with convective
initiation and maintenance for today`s event, but latest HREF run
and individual HRRR/NAM3km output have indicated certain agreement
in highlighting south-central KY and along the OH River as areas
where strongest storms could manifest, although eastern third of the
forecast area is still included in the Slight severe risk probably
due to the combination of better low-level winds and better
instability parameters. As highlighted in previous discussions, there
is a marginal risk of severe storms this afternoon and early evening
based on moderate instability, decent 0-3 km lapse rates, and
slightly enhanced wind signal in the lowest levels as a 25-30 kt LLJ
departs the area. On the other hand, effective bulk shear will
oscillate around 25 knots which will support multicell clusters or
pulse cellular convection as the main convective modes. Strong to
marginally severe storms will be capable of brief damaging wind
gusts, lightning, and small hail. Heavy rain will also be common
with these storms as a 2+-inch PW tongue is advected into the region
by the convergent branch of the MCV.

Tonight...Expect a drying trend around midnight and thereafter as
the cold front keeps pushing to the south, winds shift from the west
to the north, and mid-level subsidence takes over. A residual
saturated layer, from this afternoon/evening heavy rain totals, will
most likely linger in the post-frontal airmass and increase the
chances of low stratus or fog instances later tonight into Thursday
morning. MOS guidance has recently picked up on this signal, but it
remains unclear the thickness and coverage of any potential
visibility obstructions.

Thursday...Surface high pressure transitioning over the Great Lakes
and raising mid-level heights due to the building ridge will
maintain mostly sunny conditions. A brief relief from the hot and
humid conditions is also expected as dewpoints fall to the low 60s
and highs stay in the mid to upper 80s, not quite the drop desired
but that will have to do for now as the long term features rising
temperatures once again.

&&

.LONG TERM /THURSDAY NIGHT THROUGH WEDNESDAY/...
Issued at 314 PM EDT Wed Jun 26 2024

Thursday Night through Friday Night...

At the beginning of the forecast period, high pressure is forecast
to be over the Great Lakes with a frontal boundary draped across the
southeast US.  Flow aloft will transition to more of a zonal regime
with mainly clear skies for Thursday night and mostly sunny
conditions for Friday and into Friday night.  Combination of clear
skies and light winds should result in good radiational cooling
across the region.  Lows Thursday  night will drip back into the low-
mid 60s on the ridges with mid-upper 50s in the valleys.  Good
insolation is likely on Friday with an increasing southwesterly flow
which should allow afternoon highs to warm into the upper 80s and
lower 90s.  The southwest flow will continue Friday night and will
not allow temps to fall as much as Thursday night.  Overnight lows
Friday night will only fall into the lower 70s in most spots.

Saturday through Sunday Night...

During the day on Saturday, a fairly strong upper level trough axis
will move along the US/Canadian border into the Great Lakes.  As
this occurs, surface low will move eastward in advance of the upper
trough with a southward trailing cold front approaching the Ohio
Valley from the northwest.  Ahead of the cold front, strong heating
is expected during the day on Saturday with highs warming into the
upper 80s and lower 90s.  Dewpoints are likely to pool into the
upper 60s/lower 70s in advance of the front yielding heat index
readings in the upper 90s to the lower 100s.  Model soundings
continue to show tall/skinny CAPE profiles with PWATs increasing
from 1.8-1.9 to 2.0-2.1 inches (normal for late June is 1.3 inches).
Combination of deep moisture with high freezing levels suggests slow
moving storms capable of producing torrential rainfall.  With the
model soundings exhibiting a tall/skinny CAPE profile,
microbursts/damaging wind threat looks to be in place here.  Shear
profiles remain quite weak for organized convection, but given the
expected instability, I suspect that a marginal severe storm risk
will likely be needed in the Sat/Sat night period.  The slow
movement and high PWAT values also may lead to some localized flash
flooding.

Convection should continue into the Saturday night period with a
gradual diminishing trend with the loss of heating and increasing
CINH in the PBL associated with nocturnal cooling.  Some additional
convective redevelop may occur Sat night with additional
perturbations moving through with the flow.  However, most
convection should clear the area by early Sunday afternoon.

Lows Saturday night will be in the lower-mid 70s. Highs on Sunday
should be a bit cooler with highs in the mid-upper 80s.  Lows Sunday
night will drop back into the upper 60s to the lower 60s.

Monday through Wednesday...

As we move into the new work week, upper level trough axis will move
off to the east and ridging will build into the area from the west.
Monday and Tuesday should feature dry conditions with an increase in
temperatures through the period.  Highs Monday will be in the low-
mid 80s but will increase back into the upper 80s/lower 90s by
Tuesday.  Upper level ridging will likely hold on into the day on
Wednesday but a series of shortwave troughs aloft will likely start
to knock down the ridge a bit and may result in isolated-scattered
storms returning by Wednesday afternoon.  Highs Wednesday will
likely be in the in the lower 90s.

&&

.AVIATION /18Z TAFS THROUGH 00Z FRIDAY/...
Issued at 314 PM EDT Wed Jun 26 2024

Impacts/Confidence:
- Medium confidence in storm-related impacts late this afternoon and
evening.
- Medium confidence in MVFR VIS and CIGS tonight after the storms.

Discussion...Current VFR conditions and quiet weather will come to
an end late this afternoon as a cold front and attendant storms drop
through the region. Best timing for storm-related impacts (MVFR or
even IFR ceilings and/or visibility) is from 5-9 pm with a gradual
recovery from there until midnight. Meanwhile, winds will remain
light and slowly turning from west to northwest this afternoon with
gusty winds greater than 20 knots embedded in the storms. Then, a
saturated environment in the wake of the storms will probably
promote MVFR stratus/fog instances later tonight into Thursday
morning.

&&

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

&&

$$

SHORT TERM...ALL
LONG TERM....MJ/REJ
AVIATION.....ALL