379
FXUS63 KLMK 040505
AFDLMK

Area Forecast Discussion
National Weather Service Louisville KY
105 AM EDT Thu Sep 4 2025

.KEY MESSAGES...

* Two cold fronts will bring additional chances for rain tonight
  into Thursday and Friday night/Saturday. Rainfall amounts may make
  minor improvements to drought conditions, though drought removal
  is unlikely.

* Cooler and drier air returns by Sunday.

&&

.UPDATE...
Issued at 105 AM EDT Thu Sep 4 2025

Surface cold front is just northwest of the forecast area early this
morning.  Ahead of the front, a band of showers and thunderstorms is
steadily moving through southwest Indiana.  This activity will
spread east-southeast and should cross into the I-65 corridor around
300 AM EDT.  Atmosphere ahead of this activity is not all that
unstable with about 500-750 J/kg of MLCAPE and 20-25kts of bulk
shear.   This should keep the storms going for the next several
hours as frontal slab ascent should compensate for rather meager
instability profiles.  Heavy rainfall, wind gusts to 40-45 mph, and
frequent lightning will be possible with this activity as it heads
into the Louisville metro region over the next few hours.

Issued at 951 PM EDT Wed Sep 3 2025

All is quiet at this hour with southerly flow and mostly clear
skycover. However, satellite imagery shows the cloud deck associated
with a cold front approaching our area from the northwest, and we
will see increasing clouds shortly. The front is noted along or just
north of the I-70 corridor, and will continue to slide southeast
toward our area overnight. Still expecting our area to remain dry
until after midnight, but as some of the latest CAMs suggest it may
be 06z and after.

Overall forecast remains in good shape with no changes planned at
this time.

&&

.SHORT TERM /THROUGH FRIDAY/...
Issued at 351 PM EDT Wed Sep 3 2025

Scattered showers and thunderstorms have developed this afternoon
across east central and southern Kentucky as a modestly unstable
environment with around 2000-2500 J/kg SBCAPE is present. Areas to
the north and west have seen some scattered cumulus clouds develop;
however, a pocket of drier air aloft has mixed down to the surface,
lowering dewpoints and limiting instability along and north of the
Kentucky Parkways. This area of drier air is expected to spread east
across north central KY over the next few hours, with the main area
of showers and storms expected to shift into southern KY by late
afternoon.

This evening into early tonight, most of the showers and storms
should diminish with the loss of daytime heating, though a few
isolated showers may continue into the early overnight hours. An
upper-level trough will descend into the Midwest overnight, bringing
a surface cold front into the region after midnight. Ahead of this
front/upper trough, low-level response from height falls aloft
should support the development of a 30-35 knot SW LLJ, particularly
along and south of the Ohio River. This LLJ will bringing warm and
moist air into the low-to-mid levels, steeping lapse rates and
increasing instability aloft. This should lead to an increase in
showers and thunderstorms along and just ahead of the cold front as
it approaches the Ohio River in the pre-dawn hours tomorrow.

Most model soundings show a fairly meager amount of instability,
with between 500-1000 J/kg in the 12Z HREF mean MUCAPE field over
central and southern KY. Additionally, sounding profiles do show a
poor lapse rates within the boundary layer, so it should be fairly
difficult to get any strong winds down to the surface. As a result,
would expect the severe threat to be pretty low with convection
tonight. While HREF localized probability-matched mean QPF progs do
show high-end potential of 2" of rain in the heaviest swaths tonight
into tomorrow morning, the most likely rainfall amounts will be
between 0.25-0.75", with even less possible across far southern KY.

The cold front will be slow to push through the region tomorrow,
with showers and thunderstorms likely continuing across south
central and east central KY through the morning and into the early-
to-mid afternoon hours before exiting by early evening. South of
ongoing convection, areas may be able to destabilize enough to
realize some stronger wind gusts at the surface during the late
morning and afternoon hours. This is likely why the SPC has
highlighted a marginal risk for damaging winds south of the Kentucky
Parkways.

Through the late morning and afternoon hours, drier air will work in
behind the cold front, bringing a gradual end to clouds and
precipitation from NW to SE. Cold advection behind the front
combined with low cloud cover will keep temperatures down tomorrow
across north central KY and southern IN, with highs only expected to
reach the low-to-mid 70s. Farther south, where some heating may
occur in the morning, temperatures should be warmer, with highs
potentially reaching the upper 70s and low 80s.

&&

.LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/...
Issued at 351 PM EDT Wed Sep 3 2025

Thursday Night - Saturday...

A bit of a topsy-turvy pattern is in store for the end of the week
across the region. While the mean longwave trough will remain
established over the eastern half of North America, the leading
shortwave which will bring the front tonight into tomorrow will
quickly lift northeast Thursday night as another shortwave amplifies
over the mid- and upper-Miss. Valley. Before this second shortwave
brings another cold front into the region, there should be
considerable recovery of the warm sector on Friday as southwest
winds bring warmer temperatures and higher dewpoints back into the
area. Highs should be some 10-15 degrees warmer across the area on
Friday, and there should be a strong gradient between highs in the
low 80s across southern IN to highs reaching the low 90s across
southern KY.

Increasing moisture should allow for some instability to develop
Friday afternoon, with medium-range guidance showing between 1500-
2500 J/kg of SBCAPE, particularly across Kentucky. Stronger cyclonic
flow around the base of the trough should provide broad support for
ascent, and the sfc cold front may also be close enough to provide a
trigger for convection Friday afternoon and evening. Additionally,
stronger flow aloft (30-35 kt bulk shear) should support more
organized convection. As a result, there is a modest threat for
strong to severe storms Friday afternoon and evening, and this
thinking is supported by AI/ML convective hazards guidance. At this
time, it looks like gusty winds would be the main threat with
storms, though more details on timing and confidence will come as we
begin to get CAM guidance over the next 24-36 hours.

Showers and thunderstorms should continue Friday night, gradually
diminishing in intensity and coverage as we lose instability. The
slower trend in the cold front`s southward progression Saturday has
continued with today`s 12Z guidance, with showers appearing to be
more likely than not across much of the southern 2/3 of the CWA on
Saturday. With the front draped over the area on Saturday,
temperatures will drop once again, with highs only expected to reach
the low-to-mid 70s.

Late Weekend and Early Next Week...

By Saturday evening, the passage of the second shortwave should help
push the cold front through the area as drier air brings and end to
rain chances. Cool, dry northerly flow should set up over the region
for Sunday into Monday as high pressure moves across the lower Great
Lakes. Temperatures should be about 10-15 degrees below normal, with
highs in the 70s and lows in the mid-to-upper 40s and lower 50s.

As we head into the middle of next week, the upper level trough over
the eastern CONUS will retreat to the north as upper ridging over
the southwest US creeps eastward. While temperatures should begin to
warm next Tuesday into Wednesday, dry conditions are likely to
continue as higher moisture remains blocked to the southwest of the
region. All in all, fairly pleasant conditions are expected for the
first half of next week.

&&

.AVIATION /00Z TAFS THROUGH 06Z FRIDAY/...
Issued at 1254 AM EDT Thu Sep 4 2025

Surface cold front to the northwest will move southeast this
morning.  Band of showers and storms out from near KHNB to KEVV will
move eastward across southern IN and north-central kY this morning.
Current tracking has this complex coming into the KSDF terminal
around 04/07Z.  Expect southwest winds ahead of the front of 8-10kts
and then we`ll see some gusts of 20-25kt...maybe 30kts as the line
goes through.  Elsewhere, will be carrying some VCTS over at KLEX
for some scattered cells that may pop up ahead the main line. Expect
this to enter the KLEX terminal later this morning, after 04/09-10Z.
For KBWG, mostly a quiet night though some storms may approach the
terminal in the 04/09-11Z time frame.

No real changes to the previous forecast after sunrise.  Cluster of
convection will likely be moving through north-central and east-
central KY during the morning hours.  Look for Cigs to drop into the
MVFR range for a time before lifting to VFR after 04/18-20Z.  Winds
during the day will be westerly at 8-10kts.

&&

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

&&

$$

UPDATE........MJ/CJP
SHORT TERM....CSG
LONG TERM.....CSG
AVIATION......MJ