273
FXUS63 KLMK 201117
AFDLMK

Area Forecast Discussion
National Weather Service Louisville KY
717 AM EDT Sun Jul 20 2025

...Updated Aviation Discussion...

.KEY MESSAGES...

* Waves of showers and thunderstorms will continue today through
  Tuesday. Gusty winds, torrential rainfall, and lightning are
  expected with storms. A Slight Risk (level 2/5) for severe weather
  has been issued for the damaging wind potential today.

* Swaths of heavy rainfall amounts are expected over the next few
  days, which may lead to flash flooding. A Flash Flood Watch has
  been issued through Monday afternoon.

* Outside of showers and storms, temperatures will warm into the low
  90s today, with heat indices approaching the mid 100s.

* Hot and very humid mid to late next week, with prolonged
  significant impacts from excessive heat possible.

&&

.SHORT TERM /THROUGH TONIGHT/...
Issued at 351 AM EDT Sun Jul 20 2025

This morning, quiet conditions are present across central KY and
southern IN, with a mix of clear skies and patchy low stratus
showing up on nighttime microphysics satellite imagery. The nearest
convective activity as of 07Z is located over northern MO and IA,
where a mesoscale convective complex has developed in the vicinity
of a subtle mid-level shortwave. This feature is expected to push
across the Midwest and head into the Ohio Valley later this morning,
and our chances for showers and storms later today appears to be
dependent on how convection initiates along and ahead of this
feature.

The synoptic setup for today has shifted slightly from the past few
days, with upper level ridging spreading west from the southeast US
toward the lower Miss. Valley as an upper trough begins to move
across southeast Canada. This will place our area into a zonal mid-
and upper-level flow pattern, though this will becoming increasingly
northwesterly as we head into tonight. A sfc front is currently
analyzed from near the Quad Cities up toward the lower peninsula of
Michigan. This front will gradually sag south toward I-70 today,
with the greatest concentration of convection expected to track in
the front`s vicinity.

Across most of the area, we should initially be dry today, with a
mix of sun and clouds helping temperatures to warm through the
morning hours. If convection does not impede warming, we should be
able to make it into the upper 80s and low-to-mid 90s by this
afternoon. With dewpoints ranging from the mid 70s to near 80
degrees, this will lead to heat indices ranging from 103-109 from
along I-65 and points west. As such, the heat advisory looks to be
in good shape, although earlier development of showers and storms
than expected could cause the advisory to bust in places.

Later this morning, hi-res guidance takes the bulk of the storms
with the aforementioned MCS into central IN, though it does have
some propagation along the southern flank. As is typical, guidance
has the MCS tracking along an instability gradient which is expected
to set up over central IN and southwest OH/northeast KY. Across our
area, 2500-3000 J/kg of MLCAPE is expected to develop, so the
environment will be fairly unstable and supportive of convective
development. Within any bowing segments which develop, a damaging
wind threat would exist, with HRRR machine learning guidance and
Nadocast having enhanced probabilities of severe winds across the
northeastern half of the CWA. SPC Day 1 slight risk reflects these
probabilities, and a few strong to severe storms will be possible.

With this being said, it still looks like the greater overall
potential will be for flash flooding, especially where convection
tries to propagate upstream or trains. The environment is still
extremely muggy, with PWATs running between 2-2.25" and model
guidance showing values up to 2.5" just to the north of us. This
should lead to torrential rainfall rates in stronger storms. Most hi-
res guidance members have several MCSs moving across the region
today into tomorrow, with localized heavier QPF swaths showing up in
the data. Of particular concern is the potential for convection to
develop along outflow boundaries later tonight as a LLJ develops.
Given the consistent signal for localized heavy rainfall swaths
today into tomorrow, have issued a Flash Flood Watch for portions of
the CWA. Many locations within the watch, especially on the southern
edge, may not see thunderstorms until late tonight or Monday;
however, thought it would be prudent to go ahead and elevate the
messaging at this time.

&&

.LONG TERM /MONDAY THROUGH SATURDAY/...
Issued at 351 AM EDT Sun Jul 20 2025

Monday through Tuesday Night...

On Monday, the center of the upper level ridge will shift westward
toward the lower Miss. Valley as a trough moves across the northeast
US and the Canadian Maritimes. The sfc boundary which will serve as
a focus for additional waves of showers and storms now through
Tuesday will gradually slide to the southeast, placing it across
southern IN and central KY Monday into Monday night. As a result,
Monday should be the most active day for showers and storms during
the extended forecast. High temperatures Monday will be determined
by the amount of convective activity, with mid-to-upper 80s expected
across the NE CWA while low 90s are expected in the south and west.

At the beginning of the forecast period, it is likely that showers
and storms will be ongoing, with each wave of storms moving from
northwest to southeast across the region, parallel to the mid- and
upper-level winds as well as an instability gradient. With
seasonably strong mid-level flow in place, each MCS/wave of storms
that moves through should be fairly progressive, with current
estimates of storm motion between 25 and 30 mph. Each wave of storms
would carry the typical hazards of the MCSs; that is, torrential
rainfall, lightning, and gusty, possibly strong winds.

While individual waves of storms may bring brief minor flooding
issues, the scenario which would promote more significant flash
flooding would be if any backbuilding/upstream propagation occurred
on the SW flank of an MCS. This increased residence time of heavy
rainfall rates would be troublesome, especially given how favorable
the environment will continue to be for tropical rainfall rates
(PWATs 2-2.25", warm cloud layers 13-14 kft). This setup could
easily produce rainfall amounts of 2-4+" in just a few hours. As
each wave of storms passes through, it should gradually eat into the
instability, shifting the storm track to the south and west into
Monday night.

By Tuesday, the upper ridge to our southwest will begin to build
northward. As it does so, sfc high pressure will sink into southern
Ontario and upstate NY. This should cause the sfc front over the
area to weaken and shift farther SW. At the same time, drier mid-
level air is expected to work in from the NE, reducing PWAT values,
although near-sfc moisture will still be high. This is expected to
lead to somewhat less coverage of showers and storms on Tuesday,
though isolated to scattered storms are still possible. High
temperatures are expected to reach the upper 80s and lower 90s, with
the core of the hottest temperatures still SW of the area.

Wednesday through Saturday Night...

Temperatures will increase Tuesday into Wednesday as the upper ridge
builds across the Ohio and Tennessee valleys. For Wednesday through
Friday, there is fairly high confidence that the ridge will remain
in place, with no significant changes to the synoptic pattern.
Current elevated soil moisture values should keep temperatures from
getting too high; however, low-to-mid 90s looks like a pretty good
bet during this period. With dewpoints remaining in the 70s, this
should get afternoon heat indices up between 100-110. At the same
time, there won`t be much relief at night, with temperatures only
falling into the 70s. Although details will still be worked out over
coming days, impactful excessive heat looks likely for next
Wednesday through at least Friday.

For Wednesday and Thursday, shower and storm coverage should be
greatly suppressed with broad subsidence in the vicinity of the
upper ridge. However, ample low-level moisture may lead to one or
two garden-variety showers/storms in the afternoon and evening.

By the end of the week and the first part of next weekend, there is
some model divergence on how much the upper ridge begins to break
down. In general, the GFS is quicker to break down the ridge, while
the GEM keeps the strongest ridge into next weekend. A stronger
ridge would lead to warmer temperatures and lower shower/storm
chances, while the opposite would be expected with a weakened ridge.

&&

.AVIATION /12Z TAFS THROUGH 18Z MONDAY/...
Issued at 717 AM EDT Sun Jul 20 2025

At the beginning of the current TAF period, low stratus will be the
main impact, especially at LEX/RGA as IFR ceilings gradually lift
and scatter out later this morning. Elsewhere, brief lower ceilings
are possible as low-level moisture lifts later this morning;
however, VFR conditions are favored for midday through this evening.
The chance for TSRA looks to be greatest at LEX and RGA this
afternoon, with lower chances at SDF/BWG/HNB. Winds today should be
out of the SW at 6-12 kt. This evening and tonight, additional
development of showers and storms is possible; however, confidence
is low as development will be dependent on earlier rounds of showers
and storms.

&&

.LMK WATCHES/WARNINGS/ADVISORIES...
KY...Heat Advisory from noon EDT /11 AM CDT/ today to 9 PM EDT /8
    PM CDT/ this evening for KYZ023>030-038-045-046-053-054-
     061>065-070>076.
     Flood Watch from 1 PM EDT this afternoon through Monday
     evening for KYZ025-029>043-045>049-054>057-066-067.
IN...Heat Advisory from noon EDT /11 AM CDT/ today to 9 PM EDT /8
    PM CDT/ this evening for INZ076>078-083-084-089>092.
     Flood Watch from 1 PM EDT /noon CDT/ this afternoon through
     Monday evening for INZ076>079-083-084-089>092.

&&

$$

SHORT TERM...CSG
LONG TERM...CSG
AVIATION...CSG