935
FXUS63 KLMK 200138
AFDLMK

Area Forecast Discussion
National Weather Service Louisville KY
938 PM EDT Tue Aug 19 2025

.KEY MESSAGES...

* Peak Heat index values around 105 are likely, mainly along and
  west of I-65 through early evening.

* Scattered thunderstorms are expected for some this evening into
  the overnight. The strongest storms could produce locally gusty
  winds and heavy rainfall.

* Drier and temperatures closer to normal for mid to late week.

* Below normal temperatures expected for the second half of the
  weekend into next week.

&&

.MESOSCALE...
Issued at 938 PM EDT Tue Aug 19 2025

A cluster of thunderstorms extends from northern Butler to southern
Spencer County at this hour, with convection trailing well behind
its associated outflow boundary. As these storms continue to move to
the southeast, a weakening trend has been noted in terms of
lightning and peak wind gusts over the past 30 minutes to an hour.
Earlier this evening, isolated instances of wind damage were
observed, mainly in association with downburst/microburst
signatures. Now that low-level lapse rates have decreased to around
6-6.5 degrees, less of the momentum aloft is translating to the
ground. Additionally, decreasing instability overall and convection
trailing well behind the initiating outflow has led to weaker
updrafts and convective cores overall. While a few 30+ mph gusts
will be possible over the next hour, expect mostly in the range of
20-30 mph gusts as the strongest storms move overhead.

This cluster of storms should subside by around midnight, with
showers possibly lingering into the overnight hours. Convection has
been progressive enough to stave off major flooding concerns, and
would expect this to continue as rain rates decrease over coming
hours.

Outside of the line of showers and storms, the cold front will
continue to sink through the area overnight, with light northerly
winds and lower dewpoints working in behind the front. Toward
daybreak Wednesday, low stratus and some patchy fog will be possible
in the vicinity of the front. Temperatures should fall into the
upper 60s and lower 70s across the area Wednesday morning.

Issued at 551 PM EDT Tue Aug 19 2025

While the radar and satellite imagery is clear over much of the CWA
at this time, there are numerous showers and storms to the immediate
north and west of the area. The most organized area of convection is
a line of thunderstorms roughly along US 50 at this time, which is
pushing toward our southern Indiana counties at around 20-25 mph.
This activity has fired along the surface cold front, and SPC
mesoanalysis shows a band of enhanced llvl moisture convergence in
the vicinity of where this activity is. While radar does show
evidence that some of this activity is beginning to gust out, with
3500-4500 J/kg of SBCAPE ahead of this line and the aforementioned
moisture convergence, would expect activity to continue into
southern IN and toward the Ohio River over the next 2-3 hours.

With deep-layer shear on the order of 5-10 kt, the front is serving
as the main organizing feature for convection, with isolated pulse
convection being observed along and south of the Ohio River so far
this afternoon. On the other hand, for the next 1-3 hours, steep
llvl lapse rates and DCAPE on the order of 1200-1400 J/kg will make
isolated strong-to-severe wind gusts possible where the tallest
cores develop. Further to this point, elevated values of microburst
potential are also noted across southern IN on latest mesoanalysis.

Farther to the south and west across western KY, storms have been
less organized but still sufficiently tall to produce isolated
strong to severe wind gusts. While this activity may try to creep
into Ohio/Butler/Logan County over the next few hours, generally
would expect sub-severe wind gusts and locally heavy rainfall with
this activity (if it makes it into our CWA).

The main change to the forecast at this time was to increase PoPs
over the next 3 hours over southern Indiana.

&&

.SHORT TERM /THROUGH WEDNESDAY/...
Issued at 350 PM EDT Tue Aug 19 2025

A sfc cold front cuts NE to SW from Southeast Lower MI through
central IN and southern IL this afternoon. Strong destabilization
has taken place along and just south of the boundary with rich low-
level moisture (mid 70s Tds) pooling in that area. Recent SPC
mesoanalysis shows an axis of 3000+ J/kg MLCAPE from eastern MO
northeast into west-central IN. MLCAPE of 2000-2500 J/kg extends in
southern IN and west-central KY, with less instability further east.

Scattered convection has developed along the boundary in central
Indiana. The front is forecast to sink to near the Ohio River by 00Z
this evening. Expect increasing chances for scattered showers and
storms in southern IN and portions of central KY after 5-6 PM.
Isolated strong to severe storms remain on the table, but the
overall severe risk is Marginal/low-end. The primary storm hazards
will be locally strong wind gusts, torrential rainfall, and frequent
lightning. Storm intensity will diminish by 11 pm to Midnight due to
waning instability. Weaker near sfc lapse rates should eliminate the
marginal damaging wind threat by that time. However, spotty showers
and storms will remain possible through much of the overnight period
as the cold front pushes through the area.

Sfc temperatures are currently running in the low to mid 90s. Heat
Index values range from the mid/upper 90s in the Bluegrass Region to
around 105 west of I-65. The Heat Advisory looks fairly well placed
based on obs the past two hours, so will continue it through 8 PM
with no changes.

A slightly cooler, less humid airmass begins to move into the region
Wednesday in the wake of the cold front. Morning lows will be in the
upper 60s to lower 70s. Highs in the mid/upper 80s will be common
Wednesday afternoon. A few showers and storms will be possible,
mainly in southern KY closer to the boundary. Otherwise, most can
expect a dry day with a steady north wind and partly to mostly
cloudy skies.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH TUESDAY/...
Issued at 350 PM EDT Tue Aug 19 2025

Wednesday Night - Friday Night...

Wednesday night looks quiet and dry. A light north wind continues
with high pressure centered over the Great Lakes. Temperatures are
forecast to fall into the mid and upper 60s by daybreak Thursday.

Thursday and Friday continue to look mainly dry with a light NE wind
continuing at the surface. High pressure centered off to our north
gradually weakens with time as a fairly strong low pressure system
barrels west to east across Canada. However, this system`s cold
front won`t impact our weather until later this weekend. Look for
highs in the low to mid 80s Thursday, with mid to upper 80s on
Friday. Lows Friday morning could get down as low as the low to mid
60s.

Saturday - Monday...

The Canadian storm system continues to deepen across Ontario Friday
into Saturday, pulling a trailing cold front southeast through the
Great Lakes and Midwest. Moisture briefly deepens Saturday and
Saturday night ahead of this front, which could bring some isolated
showers and storms. Highs on Saturday will be fairly typical for
this time of year in the mid 80s to around 90.

Significantly cooler air arrives for the second half of the weekend,
with a reinforcing shot of cool air from the northwest. Deep upper
level troughing takes shape over the eastern CONUS, with deep NW
flow locally. This refreshing pattern will bring notably lower
dewpoints (50s) to the region. Expect lows in the low to mid 60s
Sunday morning, with afternoon highs in the low to mid 80s. Lows in
the mid 50s to around 60 will be possible for the commute to work
and school Monday morning.

&&

.AVIATION /00Z TAFS THROUGH 06Z THURSDAY/...
Issued at 749 PM EDT Tue Aug 19 2025

A line of showers and thunderstorms associated with a cold front
will move through SDF over the next hour, and may try to approach
LEX, RGA, and BWG later this evening. The line will bring gusty NW
winds, as well as brief IFR/LIFR visibilities as it passes, though
it is expected to weaken over the next 1-2 hours. Once this line
dissipates, winds should gradually veer to the north as the front
sinks south across the region late tonight. Behind the front, there
appears to be a window for MVFR, and possibly IFR stratus,
particularly at LEX and SDF tomorrow morning. Flight categories
should improve by early afternoon on Wednesday, with post-frontal
stratus expected to mix up into a 3-5 kft stratocu field. Winds are
expected to strengthen Wednesday afternoon out of the north, with 20
kt gusts possible at SDF, LEX, and HNB.

&&

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

&&

$$

MESOSCALE...CSG
SHORT TERM...EBW
LONG TERM...EBW
AVIATION...CSG