Flash Flood Warning 121, NWS Louisville, KY

Area Forecast Discussion
National Weather Service Louisville KY
251 PM EDT Tue Aug 11 2026

...Forecast Update...

.KEY MESSAGES...

* There is a level 3 of 5 (enhanced) risk for severe weather this
  evening north of a roughly Bedford, Indiana to Richmond, Kentucky
  line, with the risk decreasing further southwest. Damaging winds,
  some significant (> 75 mph), are the primary hazard.

* Repeated rounds of heavy rainfall in thunderstorms tonight and
  again tomorrow could result in localized flash flooding. There is
  a level 2 of 4 (slight) risk for excessive rainfall.

* Additional rounds of storms are possible (40-60% chance) through
  Friday. There is a level 2 of 5 (slight) risk for severe weather
  tomorrow west of I-65, with damaging winds the primary concern.

* 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.

&&

.UPDATE...
Issued at 250 PM EDT Tue Aug 11 2026

Severe Thunderstorm Watch #568 has been issued until 8 PM EDT for
areas along and northeast of a Scottsburg, IN to Winchester, KY
line. This complex does have a history of producing wind damage
across IN and Ohio.

&&

.SHORT TERM /THROUGH WEDNESDAY NIGHT/...
Issued at 223 PM EDT Tue Aug 11 2026

Upstream complex over central IN/OH is now quickly racing SE with a
history wind damage. This bowing segment is moving into a strongly
unstable environment characterized by 3000-4000 J/KG of ML CAPE and
deep layer shear around 30-40 knots. This should allow for a decent
cold pool/updraft balance to sustain forward propagation into our NE
CWA this afternoon through early evening. Best chance for severe
storms capable of damaging winds will be along and east of a
Madison, IN to Richmond, KY line as the complex dives SE on the
notable CAPE gradient offered by the 11/17z SPC Mesoanalysis.
Although damaging winds is the main threat, can't rule out a brief
spin up on the leading edge. This would be more likely for any
portion of the line oriented more N-S as the 0-3 km shear vector is
mostly W-E. Not sure how likely this is given the pretty good
southward surge of the cold pool, but nevertheless will keep an eye
out for any brief mesovortice potential.

There is much uncertainty with regard to how much convective
activity will occur to the west of the geographic line mentioned
above. Latest runs of the HRRR suggest that this initial wave is
quite progressive and then re-initiation of storms occur in a more N-
S fashion along the western flank of the outflow boundary up over SE
IN and SW Ohio through the overnight. This is where most concern for
a Flash Flood threat could develop. Confidence remains low in this
scenario, mainly with respect to placement of that heavy rainfall
axis. It will be close whether that threat is able to be realized
into our CWA or stays just to the NE. Do have the Flood Watch up to
account for this along and east of a Madison, IN down through
Richmond, KY line. 11/12z HREF does still suggest that some
localized amounts over 3" of rain will be possible with this setup
in the PMM data, which closely matches the higher end QPF amounts
offered by the highest ensemble member. Something to keep in mind,
and it could lead to a few serious Flash Flood concerns if it
trains/persists over the same area with the low level jet feeding
into a stationary boundary. Confidence is low, but potential is also
there.

Much uncertainty for the evolution of things going through Wednesday
as much will depend on what happens this evening and tonight.
Confidence is fairly high that we will see another convective
complex later tomorrow afternoon or evening as it initiates upstream
thanks to another shortwave embedded within the NW flow aloft, and
then propagates SE through what should be an unstable and overall
favorable wind shear environment. Damaging winds would again be the
main threat, but a flooding threat could also develop, especially if
we get a good amount of rain tonight. Assuming the convectively
reinforced outflow boundary is pushed somewhat farther SW after this
evening's activity, then it makes sense that tomorrow's threat is
also a bit farther southwest as seen on the Day 2 SPC Outlook.

Current Heat Advisory looks pretty good, and don't plan to make any
adjustments to that given current obs for this afternoon. May still
need to expand the Advisory into Wednesday, but would like to have
more confidence in how tonight's convective evolution plays out
before committing to a headline tomorrow.

&&

.LONG TERM /THURSDAY THROUGH MONDAY/...
Issued at 223 PM EDT Tue Aug 11 2026

Thursday - Friday Night...

The upper ridge will center over the lower Mississippi River
Valley/Gulf Coast states for the late week time frame, with the Ohio
River Valley sitting on the NE periphery of this feature. NW flow
aloft will be in place over our area, sandwiched between the upper
ridge and a NE CONUS/Eastern Canada trough. This setup will put us
in position for continued MCS potential as we get the overlap
between strong instability and notable deep layer shear for this
time of year.

In addition to a potential severe weather threat (mainly damaging
wind), any repeated rounds of MCS activity could create or
exacerbate flooding concerns, depending on what happens through mid
week.

Heat and humidity could also continue to be a concern as
temperatures could warm into the low and mid 90s in conjunction with
low and mid 70s dew points. This will remain low confidence however,
given the potential for MCS activity to wreck a temp forecast
Thursday or Friday. Will handle any needed Heat Advisory headlines a
day at a time in this pattern. Most likely areas for any headlines
would be across our SW CWA, closes to the center of the upper ridge.

Saturday - Sunday...

The upper ridge strengthens to around 600 dam at H5 through the
weekend, and also centers more over the Ozarks region by this time.
This will put our area more solidly under the influence of the
subsident airmass associated with an upper ridge, and also slightly
more intense heat. In fact, low and mid 90s from late week could
give way to mid and upper 90s by Sunday. Some heat headlines look to
be a good bet for at least our western or southwestern half of the
CWA, if not most of the CWA.

The good news is that this should give us some reprieve from any MCS
activity as that threat would shift to the north and east thanks to
the movement of the upper ridge.

Monday - Tuesday...

The upper ridge should retrograde back toward the Red River Valley
by early next week, with NW flow aloft taking back hold of our area
as the NE periphery of the upper ridge retreats. This will allow a
weak frontal boundary trailing from a New England system to drop
into our region. Some mainly diurnally driven convection could occur
with this weak frontal passage on Monday, however we will likely be
post-frontal on Tuesday with high pressure building in behind it.
Likely a dry forecast for Tuesday unless the front gets hung up.
Pretty good agreement right now that it makes it through so will
lean toward dry and overall cooler temperatures by Tuesday.

&&

.AVIATION /18Z TAFS THROUGH 00Z THURSDAY/...
Issued at 125 PM EDT Tue Aug 11 2026

A round of scattered showers and storms will move into the region
this evening bringing strong winds and lowered vis. The highest
confidence for strong storms will be for LEX and RGA. If the systems
tracks more westward, SDF and HNB could get some stronger storms as
well. PROB30s have been added to all sites, except BWG, due to this
uncertainty, but to rely the most likely timeframe. LEX and RGA are
expected to see multiple rounds of rain tonight into the early
morning hours. Sites should expect some variability in wind
direction with any outflow gusts. Ceilings are expected to stay VFR
,outside of possible lowered storm bases, for the remained of the
TAF period.

&&

.LMK WATCHES/WARNINGS/ADVISORIES...
KY...Heat Advisory until 8 PM CDT this evening for KYZ023-026-061-
     070>073.
     Flood Watch through Wednesday morning for KYZ032-033-035>037-
     040>043-048-049-057.
IN...Heat Advisory until 9 PM EDT /8 PM CDT/ this evening for
     INZ076-083-084-089.
     Flood Watch through Wednesday morning for INZ079.

&&

UPDATE...BJS
SHORT TERM...BJS
LONG TERM...BJS
AVIATION...CAL

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