402
FXUS63 KLMK 131703
AFDLMK

Area Forecast Discussion
National Weather Service Louisville KY
103 PM EDT Thu Aug 13 2026

...Updated Aviation Discussion...

.KEY MESSAGES...

* There is a 30-50% chance for thunderstorms this evening into
  tonight. The strongest storms this evening could generate locally
  damaging wind gusts, along with frequent cloud to ground lightning.

* Repeated rounds of heavy rainfall in thunderstorms tonight into
  early Friday could result in flash flooding. There is a level 2 of
  4 (slight) risk for excessive rainfall.

* A few additional storms (20-40% chance) may occur Friday into
  Friday night across areas mainly east of a roughly Jasper, Indiana
  to Richmond, Kentucky line. Confidence is low on whether a severe
  weather or flooding risk may develop.

* Outside of storms, heat indices are likely (60-80% chance) to
  surpass 100 degrees west of I-75 both today and tomorrow. The heat
  and humidity peaks Saturday and Sunday, when HeatRisk is forecast
  to reach the Major category area-wide.

&&

.SHORT TERM /THROUGH TONIGHT/...
Issued at 216 AM EDT Thu Aug 13 2026

***** STRONG STORM AND HEAVY RAINFALL RISK THROUGH TONIGHT *****

At 2am EDT, central Kentucky and southern Indiana finds itself on
the northeast periphery of an expansive ridge of high pressure
centered across the Great Plains. KLVX`s vad profiler revealed a
weak westerly LLJ around 20-25 kt, which is slowly bringing some
elevated instability back into our area atop the residual cold pool
from evening storms. RAP mesoanalysis suggests a rather sharp
gradient in this unstable layer rooted around 500-750 m off the
surface, with anywhere from 100 J/kg MUCAPE across areas east of I-
75 to nearly 3000 J/kg across western Kentucky. Along the edge of
this richer theta-e airmass, a few thunderstorms are sinking
southeastward across northern and eastern portions of the CWA. Given
the elevated nature of these storms, which various CAMs suggest may
linger through the pre-dawn hours, the risk of severe weather
appears low, though we`ll need to keep an eye on the hydro potential
if any backbuilding occurs in locations that already saw heavy
rainfall yesterday morning.

Of greater concern will be how the atmosphere recovers this
afternoon ahead of an organized thunderstorm cluster now moving
across Nebraska. If we get enough of a break in convective activity
later this morning into the afternoon, the RAP and NAM suggest we
could have a corridor of 2500-4000 (highest west) J/kg MLCAPE set up
across the area - more than sufficient to fuel strong to severe
thunderstorms, despite only modest (20-30 kt) deep layer shear. HREF
20km neighborhood probabilities for more than 40 dBZ reflectivity
are only 20-50% across the area this afternoon and evening,
suggesting confidence is low to medium at best in storms at all, but
the volatile environment will support a severe weather risk with any
parcels lifted through the shallow capping inversion to the
LFC. The primary hazard will once again be damaging wind gusts
from both precip-laden collapsing cores and especially with any
bowing multicell linear segments that manage to form and
propagate towards the southeast. Heavy rainfall is a concern
with the strongest storms as well, given a deep (>12kft) warm
cloud layer and PWATs > 1.8 inches; however, storm motions of
20-35 mph (fastest north) suggest it`ll take training of storms
over the same areas for that to happen.

The hydro concern will linger during the overnight period tonight
into early tomorrow morning as a 25-35 kt LLJ feeds into the
effective boundary. The CAMs suggest this front should stay off to
our north, as evidenced by the maximum in 90-10th percentile
difference in HREF theta-E, along with 6h precip LPMM. However, if
this should shift southward at all, training convection overnight
into Friday morning could result in flooding across a section of our
area - the highest risk being north of a roughly French Lick, IN to
Richmond, KY line.

Outside of storms, it`ll be a warm and muggy day with heat indices
topping 100 degrees across many locations west of roughly I-75. The
highest confidence (60-80% chance) from both the HREF and REFS in
hitting advisory criteria (105 degrees) is along and west of a
roughly Allen to Hancock County line, where a Heat Advisory is in
effect from 10am to 8pm CDT.

&&

.LONG TERM /FRIDAY THROUGH WEDNESDAY/...
Issued at 216 AM EDT Thu Aug 13 2026

***** STORM CHANCES WANE, HEAT BUILDS INTO THE WEEKEND *****

The effective boundary is forecast to drop southward into Kentucky
on Friday, possibly (30-50% chance) serving as a focus for
additional pop up storms during the afternoon mainly east of the I-
65 corridor. However, the trend should be for ridging to expand
eastward heading into the weekend, suggesting chances for showers
and storms will taper to less than 20% across the local area
Saturday into Sunday. Meanwhile, conditions will grow increasingly
hot and humid, with HeatRisk climbing solidly into the Major and
possibly (20-40% chance) into the Extreme Category by Sunday. We
remain close enough to the periphery of the ridge that if an MCS
takes a dive southward, it could (10-20% chance) wreck the
temperature forecast both Saturday and Sunday, but if that doesn`t
happen (80-90% chance) then heat indices are almost certain to
exceed 100 degrees across most/all of the area. We suspect NBM`s
forecast high temperatures might be a degree or two overdone given
evapotranspiration (ET) after recent rain is sometimes underforecast
by its inputs (global ensembles). However, the oppressive humidity
will combine with the heat to make conditions dangerous to
vulnerable populations such as the elderly, chronically ill, outdoor
workers, and those without proper cooling. In addition, it will
likely prevent overnight low temperatures from falling below the mid
70s (upper 70s in urban corridors).

***** LESS HOT, STORMS RETURN EARLY NEXT WORK WEEK *****

A shortwave trough should flatten the ridge and drop a frontal
boundary over the area sometime early next work week, potentially
offering some relief from the heat for at least a portion of the
area and serving as a trigger for showers and storms. It`s too early
to tell whether a severe weather risk may materialize with this
activity, but the joint probability of > 25 kt 0-6km bulk shear and
> 2000 J/kg MUCAPE from the LREF is less than 20%, which, at least
at this point in time, suggests the risk should be relatively low.
Given the richly moist and unstable airmass ahead of the trough and
attendant front, heavy rain and localized microbursts in water-laden
collapsing cores would seem to be the primary hazards (if any).

&&

.AVIATION /18Z TAFS THROUGH 00Z SATURDAY/...
Issued at 103 PM EDT Thu Aug 13 2026

Overall the forecast through this TAF cycle remains mostly VFR
flight categories through the period with just a few exception this
afternoon for LEX/RGA. There have been SCT/BKN MVFR and even IFR CIG
briefly already today. Decided to highlight this with keeping either
SCT008/SCT015 with tempo groups to account for some low CIGs due to
afternoon Cu field. While there is a low chance of showers and
storms later this afternoon and evening, confidence is low. Kept the
rest of the forecast VFR for all sites with just wind shift
overnight from southerly then back to southwest in the afternoon.

&&

.LMK WATCHES/WARNINGS/ADVISORIES...
KY...Heat Advisory until 8 PM CDT this evening for KYZ023-026-061-
     070>073.
IN...None.

&&

$$

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