996
FXUS63 KLMK 162342
AFDLMK

Area Forecast Discussion
National Weather Service Louisville KY
742 PM EDT Wed Jul 16 2025

...Updated Aviation Discussion...

.KEY MESSAGES...

* Isolated to scattered showers and storms continue this afternoon
  and evening, especially along and east of Interstate 65.

* Near-advisory levels of heat and humidity expected on Thursday,
  with afternoon heat indices ranging from 100-105.

* Scattered to numerous showers and storms return on Thursday. A few
  storms could have strong downbursts/microbursts resulting in
  localized damaging winds. Torrential rainfall rates may also lead
  to flash flooding.

* A continued active pattern continues into the weekend and early
  next week, with daily chances for showers and storms. Hot and
  humid weather is also expected to continue.

&&

.SHORT TERM /THROUGH THURSDAY NIGHT/...
Issued at 345 PM EDT Wed Jul 16 2025

This Afternoon through Tonight...

It is a very warm and muggy afternoon across central KY and southern
IN as temperatures range from the mid 80s to the low 90s with
dewpoints in the mid-to-upper 70s. This has led to the development
of 3000-4000 J/kg SBCAPE, and scattered showers and thunderstorms
have fired up along and east of I-65. Given PWAT values around or
slightly exceeding 2", the main threats with any storms will be
torrential rainfall and cloud-to-ground lightning, with gusty winds
expected with any taller storms which can produce a downburst. West
of I-65, subsidence in the wake of the MCV which moved across south
central IN this morning has limited convective development, although
a few agitated cu are noted on satellite.

For the rest of the afternoon, there is expected to be less coverage
of showers and storms compared to the past few days, especially
across the western half of the CWA. Temperatures should warm into
the upper 80s and lower 90s, and when combined with high dewpoints,
should lead to heat index values in the upper 90s and lower 100s. A
stronger pressure gradient in the vicinity of the departing MCV will
allowed for continued breezy SW winds, with sustained winds of 10 to
20 mph and gusts of 20 to 30 mph expected.

Tonight, an upper shortwave passing across the Great Lakes will help
to nudge a surface cold front toward the Ohio Valley. The front
should stay far enough to the north to avoid providing a trigger for
showers and storms, so we`ll have low (<20%) PoPs in the forecast
after sunset this evening. There should be enough of a pressure
gradient in place to keep a light southerly breeze in overnight,
which should limit fog potential and keep temperatures very mild
into Thursday morning. Lows tonight should only fall into the low-to-
mid 70s in rural areas, with urban heat islands expected to struggle
to fall below 80.

Thursday and Thursday Night...

The sfc cold front should approach the I-70 corridor by dawn on
Thursday, though it will struggle to sag much farther to south as
the mid-level shortwave forcing it to the south will quickly slide
toward the northeast US. To the south of the front, convergent flow
will help to pool moisture in the lowest layers of the atmosphere,
with sfc dewpoints expected to be in the mid-to-upper 70s Thursday
morning and PWATs ranging from around 2-2.25". As sfc heating ramps
up, a very unstable environment will develop across the area, with
short range progs showing around 4000-5000 J/kg of SBCAPE. Showers
and storms are expected to fire along the front between 15-17Z
tomorrow, potentially growing upscale into clusters or a broken line
and pushing to the southeast through the afternoon and evening
hours. Deep layer shear of around 15-20 kt could provide enough mid-
and upper-level flow to sustain a few stronger updrafts, resulting
in taller storms which could produce strong downdrafts and a few wet
microbursts. As a result, in addition to torrential rainfall and
frequent lightning, isolated strong to damaging winds are possible
tomorrow afternoon, with 12Z HRRR machine learning guidance
producing notable probabilities of severe wind gusts across the area
tomorrow.

Given the amount of moisture and instability present tomorrow
combined with deep warm cloud depths (on the order of 13-14 kft),
torrential rainfall rates are likely in the heaviest storms. 12Z
HREF guidance does show some swaths of 3-4" on 6-hr LPMM tomorrow
afternoon and evening, which would lead to localized flash flooding.
Agree with the increase to a Slight (15%) risk of excessive rainfall
tomorrow on the latest WPC ERO, and it is certainly possible that
several flood advisories/flash flood warnings will be needed. On the
other hand, storm motions should be around 20 to 30 mph, and the
expected southeast progression should limit residence time of the
heaviest rainfall rates. Due to lingering uncertainty in positioning
of storms and heaviest rainfall amounts, we`ll hold off on any
issuance of a flood watch, though one may be needed if confidence
increases.

Outside of the rainfall/storm threat, tomorrow will also be a hot
and sticky day across the region. Heat index values are expected to
reach 100-105 in many locations, and may reach advisory criteria
across southwestern KY. However, if storms develop faster than
expected, this could limit heating, so we`ll also hold off on any
heat advisory decisions at this time.

Tomorrow night, convection should wind down after sunset as the
resulting convective complex stabilizes the environment. With the
sfc front expected to wash out just north of the Ohio River, there
will still be a very warm and muggy environment in place, with
temperatures remaining in the 70s into Friday morning. Some hi-res
guidance tries to develop new convection early Friday morning,
though this seems highly dependent on the evolution of storms
tomorrow afternoon and evening. If additional showers and storms
were to develop, this could exacerbate any heavy rainfall/flooding
issues were they to develop tomorrow evening.

&&

.LONG TERM /FRIDAY THROUGH WEDNESDAY/...
Issued at 345 PM EDT Wed Jul 16 2025

The remnants of the aforementioned front will still linger across
the area into Friday, keeping a tropical environment in place.
Lingering cloud cover and rich moisture should keep temperatures a
few degrees cooler on Friday, with highs expected to range from the
mid-80s to around 90. This should also help to limit instability,
with soundings supporting more typical amounts of CAPE around 1500-
2000 J/kg. Further, with mid- and upper-level ridging starting to
build back over the southeast US, weaker flow aloft should reduce
deep layer shear back to around 10 kt for Friday. As a result, more
garden-variety summer shower and storms are expected on Friday,
though this will continue to carry a lingering heavy rain/flash
flood risk with it.

For the weekend and into next week, the upper level pattern is not
expected to change all that much.  SE ridge will remain in place
with a rather deep west to east flow across the Ohio Valley. Remnant
frontal boundary will likely remain in the vicinity of the Ohio
River, but am not sure it will make it south of that.  Episodic
bouts of convection are likely as remnant MCVs move along the
boundary.  Model soundings continue to show rather weak shear
thorugh the column through this period, so waterloaded downdrafts
capable of producing strong winds will be the main threat along with
torrential rainfall and plenty of lightning.

Upper level ridge may attempt to build a little more to the west
with a more northwesterly flow pattern developing across the Midwest
and Ohio Valley as we move into next week.  This could set the stage
for some MCS clusters to trail down along the periphery of this
ridge and into the region.  The overall synoptic pattern is one that
can produce excessive rainfall in the Ohio Valley during the warm
season and we`ll be watching the evolution of the pattern very
closely.  Daytime highs will remain in the upper 80s to around 90
with overnight lows in the low-mid 70s.

&&

.AVIATION /00Z TAFS THROUGH 06Z FRIDAY/...
Issued at 740 PM EDT Wed Jul 16 2025

Isolated showers are lingering across the area this evening, but the
main feature worth keeping an eye on is a line of thunderstorms
moving southeast across IL and IN. This line is expected to weaken
as it approaches our area, but can`t rule out some impact to HNB or
SDF later this evening from SHRA or TSRA. Otherwise, mainly VFR
conditions are expected for the overnight and into tomorrow.
Additional showers and storms are to be expected tomorrow
afternoon as well, which are highlighted with a PROB30 group.

&&

.LMK WATCHES/WARNINGS/ADVISORIES...
KY...None.
IN...None.

&&

$$

SHORT TERM...CSG
LONG TERM...MJ/CSG
AVIATION...CJP