384
FXUS63 KLMK 180701
AFDLMK

Area Forecast Discussion
National Weather Service Louisville KY
301 AM EDT Fri Sep 18 2026

.KEY MESSAGES...

* Unseasonably hot weather will continue for much of the area
  through at least Sunday. Barring any early day thunderstorms, heat
  indices will top out in the mid 90s to around 105 (highest
  southwest) each afternoon.

* There is a 20-40% chance for showers and storms late this
  afternoon and evening, with slightly higher chances tomorrow.
  Locally damaging wind gusts and heavy rainfall may accompany the
  strongest storms, especially tomorrow.

* A weather system will bring higher rain chances (50-60%) Monday
  into Tuesday, followed by a cooldown to more seasonable
  temperatures (highs in the 70s, lows in the 50s) by the second
  half of week.

&&

.SHORT TERM /THROUGH SATURDAY NIGHT/...
Issued at 256 AM EDT Fri Sep 18 2026

*** HOT WITH SCATTERED PM STORMS TODAY, TOMORROW ***

Early Friday morning, an expansive ridge of high pressure centered
across the Southern Plains was maintaining dry and seasonably warm
conditions over central Kentucky. Meanwhile, weaker associated
subsidence further north over Indiana - nearer the periphery of
the ridge - has allowed a few storms to fester along and south
of a quasistationry boundary which is slated to drop
southwestward across our area as a back door cool front tonight.
Ahead of this front, afternoon temperatures are likely to, once
again, climb well into the 90s near and west of I-65, and upper
80s to low 90s further east; combined with dewpoints in the mid
60s to low 70s, this will favor afternoon heat indices in the
upper 90s to around 105 - again, highest west, where the Heat
Advisory is in effect. A ribbon of moisture pooling immediately
ahead of the front during the evening will foster a couple
thousand J/kg MLCAPE, though forcing along it remains quite weak
leading to uncertainty on whether any showers or storms will
develop. We based precipitation chances off of the High
Resolution Ensemble Forecast (HREF) and National Blend of Models
(NBM), which give the area a 20-40% probability during the 5-10
pm timeframe. Since shear is weak, the chance of organized
convection is low, but the moderate instability, high PWATs
(1.8-2 inches), and steep low level lapse rates could favor both
locally gusty winds to ~40 mph and briefly heavy rainfall
(upwards of 1 inch/hour), along with cloud to ground lightning,
under the tallest core(s). As is the case with the cells over
Indiana early this morning, a few storms may fester into the
overnight ours along and ahead of the front over
central/southern portions of our area (a solution supported by
the ARW, NAMNest, and FV3), but then increasing CIN and waning
diurnally-driven instability should eventually overtake them.

Guidance generally agrees the front will slosh back northward into
central Indiana/Ohio on Saturday, keeping the hot and humid airmass
in place across our neck of the woods. However, the deterministic
GFS, ECMWF, and NAM each depict a shortwave trough flattening the
ridge Saturday evening/night, and CAMS suggest that ahead of this
feature scattered thunderstorms will develop during the afternoon
- perhaps limiting daytime highs. Given the uncertainty in when,
where, and even if storms will form, confidence is low in whether
and where a Heat Advisory may be needed for Saturday, though the
highest chances are once again across areas near and west of the I-
65 corridor in Kentucky. We`ll hold off for now on extending the
Heat Advisory in time. Given another afternoon of modest instability
(1500-2500 J/kg MLCAPE), and effective bulk shear climbing into a
marginally supportive range (20-25 kt) for severe weather with the
aforementioned trough, we may wind up with a severe storm or two
with wind as the primary hazard; SPC has our area outlooked in a
level 1 of 5 (marginal) risk for severe weather.

&&

.LONG TERM /SUNDAY THROUGH THURSDAY/...
Issued at 256 AM EDT Fri Sep 18 2026

*** HOT START TO THE WEEK, THEN TURNING COOLER ***

The unseasonably hot weather will continue on Sunday as ridging
restrengthens behind the Saturday night shortwave. In fact,
subsidence in its wake should limit the chances for pop up afternoon
storms, though this also suggests the airmass should be slightly
less humid compared to today and tomorrow. Even so, high
temperatures are slated to reach the mid 90s across parts of the
area (highest southwest), which is contributing to 20-50%
probabilities for Major HeatRisk.

At long last, a shift to more seasonable conditions is progged to
follow the passage of a cool front accompanying a more potent upper
level trough late Monday into Tuesday. Monday may remain quite
toasty - particularly across southern Kentucky where deterministic
NBM forecast highs are in the low-mid 90s - depending on when the
front arrives, but by Tuesday a cooler and drier airmass should
be pouring into the region from the north. In addition, the
deterministic models (GFS, ECMWF, CMC) suggest this trough
lingers over the Great Lakes/Northeast through at least late
next week to perpetuate continued northwest flow/cool advection.
The Low Resolution Ensemble Forecast (LREF) gives a 55-80%
(70-85%) probability high temperatures don`t climb out of the
70s by next Wednesday (Thursday) area-wide.

&&

.AVIATION /06Z TAFS THROUGH 12Z SATURDAY/...
Issued at 128 AM EDT Fri Sep 18 2026

VFR conditions should be predominant throughout the forecast period.
Light to calm winds mainly out of the southwest will switch around a
northwesterly direction later this morning, then a more notable
shift will occur behind a back door cool front during the evening. A
couple storms may (20-40% chance) fire along and ahead of that front
this afternoon-evening, so prob30 groups continue in the TAFs during
the period of highest confidence.

&&

.LMK WATCHES/WARNINGS/ADVISORIES...
KY...Heat Advisory until 8 PM EDT /7 PM CDT/ this evening for
     KYZ023>028-053-061>064-070>076-081.
IN...Heat Advisory until 8 PM EDT /7 PM CDT/ this evening for
     INZ083-084-089.

&&

$$

SHORT TERM...JRB
LONG TERM...JRB
AVIATION...JRB