167
FXUS63 KLMK 120709
AFDLMK

Area Forecast Discussion
National Weather Service Louisville KY
309 AM EDT Wed Aug 12 2026

.KEY MESSAGES...

* Waves of thunderstorms into tonight could generate severe weather,
  with damaging winds the primary hazard and a lower risk for large
  hail. The risk appears greatest (15-29%) near and west of I-65
  during the evening.

* Repeated rounds of heavy rainfall in thunderstorms through this
  evening could result in flash flooding. There is a level 2 of 4
  (slight) risk for excessive rainfall area-wide.

* Additional rounds of storms are possible (40-60% chance) both
  tomorrow and Friday, but confidence is low on severe weather and
  flooding potential each day.

* Outside of storms, heat indices are likely (50-80% chance) to
  surpass 100 degrees west of I-65 each afternoon through Thursday,
  and area-wide over the weekend.

&&

.SHORT TERM /THROUGH TONIGHT/...
Issued at 309 AM EDT Wed Aug 12 2026

***** FLOODING POTENTIAL THROUGH THIS EVENING *****

At 3 am EDT, heavy thunderstorms were located over southeast and
east-central Indiana, having formed at the interface of a 30-35 kt
LLJ and a leftover boundary from evening storms. These should
continue to drift southeast into southwest Ohio and northeast
Kentucky while additional activity backbuilds to the north and
northwest over central/northern Indiana. This suggests that the focus
for heavy rainfall and flash flooding potential will be right along
the northeast edge and just outside of our local area. However, a
few of the 00z CAMs suggest additional backbuilding towards the west
could bring repeated rounds of heavy thunderstorms into our eastern
county warning area (CWA) during the mid morning/afternoon. In fact,
the 00z HREF LPMM has pockets of over 3 inches of rainfall along and
east of roughly the I-75 corridor by 18z/2pm; for this reason, and
because heavy rainfall from last evening in parts of south-
central/southeast Kentucky has lowered the flash flooding threshold
(FFG) to less than 1.5 inches in 6 hours in spots, we`ve expanded
the Flood Watch westward to include another row of counties. While
the worst of this morning wave could stay off to the north and east,
the CAMs seem to agree that the next mid-level shortwave arriving
during the evening will spark additional storms that could prove
efficient rainmakers (>1 in/hour rates).

***** SEVERE WEATHER RISK THIS EVENING *****

The CAMs seem to broadly agree that, once again, a complex of severe
thunderstorms will develop over eastern Iowa/northern Illinois later
this morning. Their solutions diverge, however, in what happens once
that complex reaches Indiana. The latest (04z) HRRR, for example,
has the line racing eastward across northern Indiana and northern
Ohio, while the NAMNest and ARW, by contrast, suggest it will take a
dive southward over east-central Illinois and southern Indiana
during the afternoon. However, even the HRRR suggests the MCS will
lay out an outflow boundary on which additional convection will fire
during the late afternoon over central/southern Indiana, with that
activity tracking southeast into our area during the evening hours.
The main difference between the two solutions is timing, with the
ARW and NAMNest being a little faster (late afternoon/early evening
vs late evening). If this earlier outcome materializes, higher
diurnal instability would suggest a greater severe wind risk, while
the slower HRRR outcome would mean the risk will be lower, at least
for areas east of I-65. Like yesterday, hodographs exhibit modest
clockwise curvature in the lowest kilometer of the atmosphere, which
may maintain a bit of a messy storm mode, with broken linear
segments comprised of individual cells which could at times exhibit
deviant motion towards the right; in addition, the resultant 100-200
m^2/s^2 0-1km SRH could favor a brief tornado with any individual
cells, particularly right movers that realize the best low level
shear. These will also be the ones to watch for locally severe hail,
which, despite the warm and humid environment, was observed in our
area yesterday in the most robust updrafts. SPC has the area
outlooked in a level 2 of 5 (slight) risk for severe weather, with
damaging winds the primary risk but a lower chance for hail and
tornadoes.

&&

.LONG TERM /THURSDAY THROUGH TUESDAY/...
Issued at 309 AM EDT Wed Aug 12 2026

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

Global models and their ensembles agree that ridging will slowly
build over the area into the weekend. One or more additional mid-
level disturbances will offer thunderstorm chances Thursday into
Friday, mainly east of I-65, but then the MCS corridor should shift
to the northeast by Saturday. This will allow the heat to intensify
across the area over the weekend, with triple digit heat indices,
confined to areas mainly west of I-65 today and tomorrow, expanding
east to encompass the entire area both Saturday and Sunday. In fact,
there is a 60-90% (20-40%) chance HeatRisk reaches the major
(extreme) category by Sunday afternoon - suggesting an increased risk
for heat-related illness, especially among vulnerable populations
including those without proper cooling.

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 /06Z TAFS THROUGH 12Z THURSDAY/...
Issued at 208 AM EDT Wed Aug 12 2026

A thunderstorm complex over southeast Indiana is forecast to drop
southeastward, and with any backbuilding could (30-50% chance)
affect LEX and RGA later this morning. Chances are lower (20-35%) at
SDF, but elected to keep the prob30 from the 00z TAFs just in case.
The higher chance (50-70%) for widespread storms will be during the
late afternoon and evening when a storm complex is slated to dive
southeast out of Illinois and Indiana, but we elected not to upgrade
from prob30 to tempo groups given uncertainty on timing at any given
terminal. Outside of storms, VFR conditions should be predominant,
though there will be a low (10-20%) chance of an MVFR ceiling
through 13z. Light and fickle winds will switch around to
predominantly southwest by mid morning, with a few gusts up to 20 kt
during the afternoon.

&&

.LMK WATCHES/WARNINGS/ADVISORIES...
KY...Flood Watch through late tonight for KYZ032>037-039>043-
     047>049-055>057-066-067.
IN...Flood Watch through late tonight for INZ079.

&&

$$

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