249
FXUS63 KLMK 022008
AFDLMK

Area Forecast Discussion
National Weather Service Louisville KY
408 PM EDT Tue Sep 2 2025

.KEY MESSAGES...

* Scattered showers and thunderstorms will continue this afternoon
  and evening.

* Two cold fronts will bring additional chances for rain Wednesday
  night/Thursday and Friday night/Saturday. Expected rainfall
  amounts are unlikely to significantly alter current drought
  conditions.

* Cooler and drier air returns this weekend.

&&

.SHORT TERM /THROUGH WEDNESDAY/...
Issued at 408 PM EDT Tue Sep 2 2025

At this hour, scattered to numerous showers and thunderstorms
continue, mainly along and south of Interstate 64. These showers and
storms have developed thanks to increasing moisture along and south
of an inverted sfc trough which is located over the lower Ohio
Valley this afternoon. Dewpoints have surged into the mid-to-upper
60s, resulting in PWAT values between 1.25-1.5" and SBCAPE values of
around 2000-2500 J/kg. For the most part, garden-variety showers and
storms have occurred as overall wind shear remains weak. However, a
few stronger cores have produced locally gusty winds and torrential
rainfall over the past few hours.

As we head through the afternoon and evening hours, convective
evolution should be somewhat random/chaotic, depending on collisions
between rain-cooled outflow boundaries sparking new convective
development. By mid-to-late evening, the loss of daytime heating
combined with convective overturning of the atmosphere should lead
to most showers and storms diminishing, with a significant drop in
coverage expected between 00-03Z. Overnight, clouds will initially
be slow to clear as convection dissipates. However, if we are able
to realize some clearing in areas where it rains this
afternoon/evening, patchy, locally dense fog would be possible.
Temperatures Wednesday morning should fall into the upper 50s in the
cooler spots and into the low-to-mid 60s elsewhere.

On Wednesday, another stronger upper-level disturbance will begin to
approach the region from the northwest, which should help to wash
out the inverted trough over the area today. As a result, tomorrow
should be mostly dry, although some residual low-level moisture
could allow for a shower or storm, especially along and south of the
KY Parkways. Temperatures are expected to be mild, with highs in the
low-to-mid 80s.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH TUESDAY/...
Issued at 408 PM EDT Tue Sep 2 2025

Wednesday Night - Thursday Night...

An unusually amplified upper trough and an associated surface cold
front will descend from the Midwest into the Ohio Valley Wednesday
evening into Wednesday night. Ahead of the front, a 30 kt
southwesterly LLJ should help with moistening the pre-frontal
environment, with PWAT values surging to around 1.5-1.6" immediately
ahead of the line. The combination of moisture and lift associated
with the front should be sufficient for a line of showers and
thunderstorms to move across the area, with the best chances for
rain expected across north central KY and southern IN. While model
soundings do show a little bit (500-800 J/kg) of CAPE along this
line with marginal wind shear, a near-sfc stable layer and mediocre
lapse rates should limit the potential for anything severe.

Additional scattered showers would be expected to develop behind
FROPA during the day Thursday, with showers clearing from NW to SE
during the afternoon. With W/NW winds behind the front bringing some
cold advection into the area as well as aforementioned clouds and
showers, Thursday should be a cool day for early September, with
highs only expected to reach the mid 70s in most areas. Portions of
southern KY will still top out around 80 Thursday afternoon.
Thursday night, cooler and drier air will briefly work into the
area, allowing for temperatures to fall into the 50s in most areas
under mostly clear skies.

Friday - Saturday Night...

Thursday evening into Friday morning, the lead shortwave which will
bring the front through on Thursday will lift sharply to the
northeast as a second shortwave begins to descend over the upper
Mississippi Valley. Upper-level ridging and southwest flow will
build back into the Ohio Valley ahead of a second cold front during
the day on Friday. As a result, the cool down in temperatures on
Thursday will be short-lived as highs Friday should surge back into
the mid-to-upper 80s in many areas, while portions of southern KY
may make it into the low 90s. Friday is also likely going to be a
breezy day for early September, with a seasonally strong 850 mb jet
allowing for wind gusts on the order of 15 to 25 mph, with some
localized 30 mph gusts likely.

There continue to be differences in the secondary trough/frontal
passage between the various medium-range guidance suites. The GFS
continues to be slightly faster and more amplified with the
disturbance, bringing drier air into the region quickly on Saturday
and limiting rain chances with this front/upper wave. On the other
hand, the ECMWF depicts and alternative scenario with a slower/less
amplified second wave which would keep elevated PWATs over portions
of the lower Ohio Valley into Saturday afternoon. This solution
would bring better chances of rain Friday night into Saturday
morning, especially outside of southern and eastern KY.

Drier and cooler air should finally sink into the area by Saturday
night, allowing temperatures to fall into the upper 40s and low-to-
mid 50s Sunday morning and ending rain chances at least for the
second half of the weekend.

Sunday - Monday Night...

The best chance for dry weather and fall-like temperatures is
expected on Sunday as the cold front clears the region to the south
and east. Highs Sunday are expected to be in the mid-to-upper 70s
with lows Sunday night falling again into the 40s and low-to-mid 50s.

As we head into early next week, models diverge on how quickly the
air mass modifies as longwave troughing gradually lifts to the north
and east. The GFS (as usual) is faster in ejecting the initial
trough into the Canadian Maritimes, with a second closed low sinking
into the mid-Mississippi Valley on Monday. This brings higher PWATs
back into the area Monday afternoon, with an unsettled pattern
continuing through the first half of early next week.

On the other hand, the ECMWF keeps the cooler/drier air mass in
place for 18-24 hours longer, with Monday being another pleasant/dry
day. The moisture return in this scenario doesn`t really begin until
late Monday night, with chances for showers and storms returning
next Tuesday.

For now, we`ll keep a dry forecast going for Monday, monitoring for
any shifts in the medium-range guidance later this week.

&&

.AVIATION /18Z TAFS THROUGH 00Z THURSDAY/...
Issued at 146 PM EDT Tue Sep 2 2025

Showers and thunderstorms have blossomed across the region over the
past 1-2 hours, and are expected to continue through the mid-to-late
evening hours. The greatest coverage is expected to be at
BWG/LEX/RGA, with more isolated TSRA possible near SDF. With a low
pressure axis extending over the region, wind directions will be
quite variable today, though speeds should generally be 10 kt or
less outside of TSRA where stronger gusts are possible.

Tonight, SHRA/TSRA should diminish, especially after 03Z, with VFR
conditions expected for the early overnight hours. By around sunrise
Wednesday, patchy IFR/MVFR fog or low stratus may impact area
terminals, in particular RGA and BWG; however, confidence was too
low to carry in the forecast at this time.

Otherwise, mostly VFR conditions and SW winds between 6-10 kt are
expected for the day on Wednesday. A stray shower or storm cannot be
ruled out, particularly at RGA/BWG.

&&

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

&&

$$

SHORT TERM...CSG
LONG TERM...CSG
AVIATION...CSG