513
FXUS63 KLMK 221056
AFDLMK

Area Forecast Discussion
National Weather Service Louisville KY
656 AM EDT Tue Jul 22 2025

...Updated Aviation Discussion...

.KEY MESSAGES...

* Patchy, locally dense fog, is expected across south central
  Kentucky this morning.

* Drier weather today with only a stray shower or storm expected,
  mainly across south central Kentucky.

* Hot and very humid for the second half of this week into the
  weekend, with prolonged impacts from excessive heat possible.

&&

.UPDATE...
Issued at 547 AM EDT Tue Jul 22 2025

KY Mesonet cameras are showing fairly dense fog across many areas
east of I-65 across south central KY. Although the lowest ob at KGLW
is only at 1/2 mile vis, several sites in across the TN border and
in southeast KY have reported 1/4 mile or less. As a precaution,
have issued a dense fog advisory for the southeastern CWA
through 13Z.

&&

.SHORT TERM /THROUGH TONIGHT/...
Issued at 357 AM EDT Tue Jul 22 2025

Early this morning, dry conditions are present across much of the
region, with just a few showers showing up across southwestern KY
and middle TN. A NW-SE oriented backdoor cold front will try to push
southwestward through the pre-dawn hours. Lower dewpoints are the
main difference on the "cool" side of the boundary, with upper 50s
and lower 60s dewpoints spreading into northern KY at this hour.
Dewpoints have fallen into the mid-to-upper 60s across areas east of
I-65 and along/north of I-64, with dewpoints remaining in the low-to-
mid 70s south of the boundary. For areas where low-level moisture
remains high, patchy fog has begun to develop, and is expected to
become more widespread during the pre-dawn hours. Areas across south
central KY which received rain today may also see dense fog, and an
SPS or possibly a dense fog advisory may be needed pending obs
trends over the next 1-3 hours.

Today, upper-level ridging will build over the lower Mississippi
Valley, with heights beginning to increase over our area by this
afternoon. This should stall the southwestward progression of the
backdoor front, which should begin to dissipate later today. Early
morning fog will gradually lift into a stratocu field by late
morning, allowing temperatures to warm into the 80s. While upper-
level heights will increase, low-level thicknesses should only
marginally rise today, so would expect temperatures fairly similar,
maybe 1-2 degrees warmer, than on Monday. This would give us highs
in the upper 80s and lower 90s. Afternoon heat indices do get close
to 105 degrees from Ohio down to Allen County and points southwest;
however, this is fairly similar to much of the last week, and since
it`s marginal, we`ll hold off on issuing a heat advisory at this
time.

Precipitation chances will be considerably lower today across the
area thanks to the ridging building to the west. However, a stray
shower or storm will still be possible within the humid air mass
across south central KY, though coverage is only expected to be 10-
20%.

Tonight, any lingering showers/storms should dissipate quickly after
sunset, with mostly clear skies expected overnight. Some patchy fog
may try to develop, especially in valleys and near bodies of water,
though coverage should be less than this morning. More cooling will
be able to take place within the drier air mass to the north of the
leftover boundary, so lows should range from the upper 60s and lower
70s across the southwestern third of the CWA to the mid 60s across
the northeastern third.

&&

.LONG TERM /WEDNESDAY THROUGH MONDAY/...
Issued at 357 AM EDT Tue Jul 22 2025

Upper-level ridging will build and spread across the Ohio Valley on
Wednesday, with temperatures expected to warm into the low-to-mid
90s for highs. While these temperatures aren`t particularly unusual
for late July, dewpoint temperatures will be high enough to get heat
indices to around 100-105 Wednesday afternoon. It is still a bit
uncertain as to whether or not a heat advisory will be needed on
Wednesday, as the plume of greatest moisture and highest dewpoints
is expected to remain just west of our area, suppressing heat
indices somewhat. By Thursday, the center of the upper ridge and sfc
high pressure will shift slightly to the east, allowing for more
southerly flow and moisture return into the area. This should lead
to an increase in heat indices across the area, increasing the risk
for heat-related illnesses and complications. Regardless of what the
exact heat index will be, folks should take heat-related precautions
during this stretch of hot and humid weather.

Most of the area should remain dry on Wednesday and Thursday as
broad subsidence will take place under the upper ridge and a well-
defined trigger will be lacking. One or two air mass showers/storms
could develop along differential heating boundaries; however, these
should be few and far between.

Precipitation chances will begin to increase on Friday as upper-
level shortwaves sliding across the Great Lakes begin to cut into
the northern extent of the ridge. A surface front will try to sink
to the south, but will likely get hung up over northern IL/IN/OH.
Still, showers and storms originating along the front may be able to
sink into southern IN Friday evening before shower/storm chances
increase for most of the area for Saturday and Sunday. This should
cause temperatures to decrease slightly for the first part of the
weekend, though it will still be hot and humid with highs in the
upper 80s and lower 90s.

For the second half of the weekend into early next week, there are
only minor disagreements in medium-range guidance, with the upper
ridge expected to build back up, this time slightly farther west
across the central Plains. If this scenario is borne out,
temperatures would increase and precipitation chances would likely
decrease as we head into early next week.

&&

.AVIATION /12Z TAFS THROUGH 18Z WEDNESDAY/...
Issued at 656 AM EDT Tue Jul 22 2025

Areas of fog and low stratus are present across the region this
morning, with anywhere from VLIFR to VFR conditions being observed
at area terminals. The highest confidence in VFR conditions over the
next few hours is at SDF, with satellite imagery showing either fog
or low stratus near or over other terminals. Improving conditions
are expected at all terminals by late morning, with moisture mixing
out into a VFR stratocu field for the afternoon. Winds should be out
of the northeast today between 5-10 kt, becoming light and variable
after sunset tonight. Patchy fog may impact terminals again
Wednesday morning, but confidence is low enough to refrain from
mention at all sites except BWG.

&&

.LMK WATCHES/WARNINGS/ADVISORIES...
KY...Dense Fog Advisory until 9 AM EDT /8 AM CDT/ this morning for
     KYZ063>066-073>078-081-082.
IN...None.

&&

$$

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