LMK issues Area Forecast Discussion (AFD) at Aug 26, 3:26 AM EDT
415
FXUS63 KLMK 260726
AFDLMK
Area Forecast Discussion
National Weather Service Louisville KY
326 AM EDT Tue Aug 26 2025
.KEY MESSAGES...
* Well below normal temperatures continue this week. Overnight lows
will drop into the 40s in places, with highs warming into the
upper 70s/lower 80s.
* Drought conditions are likely to continue/expand as little to no
rainfall is on the immediate horizon.
&&
.SHORT TERM /THROUGH TONIGHT/...
Issued at 325 AM EDT Tue Aug 26 2025
Longwave upper troughing is now established across the eastern half
of the CONUS with a shortwave noted over Lake Michigan early this
morning that will sink southeastward toward the middle Ohio Valley
later today. At the surface, 1024 mb high pressure is centered over
western IA, and as the above-mentioned shortwave moves east later
today, it likewise will slide southeastward, settling over the Ohio
Valley by Wednesday morning.
On current nighttime microphysics satellite imagery, the high clouds
which helped to provide a spectacular sunset Monday evening have
been suppressed into the Tennessee Valley, with mostly clear skies
observed across the area. With the pressure gradient now weak enough
that most areas have decoupled, there is a wide range in
temperatures at this hour, from the upper 40s in sheltered rural
areas to near 60 in the middle of the Louisville heat island. As we
head toward dawn, temperatures should fall a few more degrees,
ranging from the mid 40s to the mid 50s across the area.
Another beautiful day is expected today, with well below normal
temperatures for late August continuing. As the upper shortwave
passes to our northeast, a few extra diurnal cumulus clouds are
likely during the late morning and afternoon hours, particularly
north of I-64 and east of I-65. While deep mixing should send
dewpoints crashing into the 40s this afternoon, weaker mid-level
flow should keep NW winds lighter today than in previous days. Highs
should range from the mid 70s to around 80 degrees.
Tonight, as high pressure settles into the area from the northwest,
mostly clear skies are expected after sunset with light and variable
winds expected overnight. Near ideal radiational cooling conditions
should allow temperatures to fall quickly in rural areas, with urban
areas lagging slightly behind. Wednesday morning will likely be the
coolest of this entire stretch, with lows approaching record values
(see the climate section for more information on this). Would expect
rural areas to predominantly fall into the mid-to-upper 40s, with
low-to-mid 50s expected in urban areas.
&&
.LONG TERM /WEDNESDAY THROUGH MONDAY/...
Issued at 325 AM EDT Tue Aug 26 2025
Synopsis...
An anomalously strong upper-level trough will be present along the
eastern half of the CONUS through the rest of this week, with strong
surface high pressure continuing to sink into the Ohio Valley
through Wednesday. A secondary upper shortwave will slide across the
northeast US Thursday afternoon through Friday, bringing a sfc front
southward across the Great Lakes and into the Midwest. While there
will be greater moisture along this front than the pre-existing dry
air mass, overall, moisture return will be fairly sparse ahead of
this system. The best forcing with this system will likewise be to
the northeast of our area, with the aforementioned cold front
weakening the farther southwest you go.
By Friday night, the upper trough axis should be east of the
Appalachians, with NW mid- and upper-level flow expected through
much of the weekend. Another area of anomalously strong sfc high
pressure will approach the region behind the late-week front; medium-
range guidance is split on how far south the heart of this cool, dry
air mass pushes. Nevertheless, with this air mass at least in the
vicinity of southern IN and central KY, precipitation chances will
remain limited and temperatures should remain below normal through
early next week.
Wednesday - Friday Night...
As high pressure moves across the region Wednesday into Thursday,
dry weather and continued below-normal temperatures are expected.
Time height plots show ample dry air above 800 mb on Wednesday, and
soundings suggest that diurnal mixing should be able to transfer
some of that dry air down to the sfc. As a result, another day of
dewpoints crashing into the 40s during the afternoon is likely, and
we'll continue to go on the low side of guidance for RH values. By
Thursday, some mid-level moisture return will begin, so dry air
mixdown will become somewhat more uncertain. While drying of fuels
will continue over the next few days, gradient winds should be
lighter on Wednesday and Thursday, so critical fire conditions
appear unlikely at this time.
Big diurnal ranges of 25-30 degrees will continue for the second
half of the week, with hi/lo temps gradually stepping up ahead of
the late week front, but still remaining below normal. While the
vast majority of medium-range ensembles keep a dry forecast going
through the extended period, there is a very low (<10%) chance for a
shower on Friday along the front. The most likely scenario is that
the front just brings increased clouds and a wind shift as we head
into the weekend.
Saturday - Monday...
The Labor Day weekend should feature continued below normal
temperatures and dry weather across central KY and southern IN. With
sfc high pressure centered over the lower Great Lakes, anticyclonic
northeasterly low-level flow should continue to advect cool and dry
air into the region. By the second half of the weekend into early
next week, there is some model divergence as the deterministic GFS
begins to bring moisture back into the region from the south, while
the ECMWF keeps dry air firmly established overhead. The
preponderance of medium-range ensembles align with the drier
solution, so we'll keep a dry forecast through the extended period
at this time. Temperatures should warm slightly over the weekend
into early next week, with highs currently expected in the upper 70s
and low-to-mid 80s, and lows expected in the mid-to-upper 50s and
lower 60s.
&&
.AVIATION /06Z TAFS THROUGH 12Z WEDNESDAY/...
Issued at 122 AM EDT Tue Aug 26 2025
Continued VFR conditions are expected through the current forecast
period. Sfc high pressure will continue to approach the region later
today, with the gradient winds relaxing slightly compared to Monday.
Still, by early afternoon, would expect sustained NW winds between 6-
10 kt with a few 15-20 kt gusts likely. A scattered cu field should
also develop for late morning through early evening today, with
cloud bases generally between 5-7 kft. Winds should become light
after sunset tonight with any cu diminishing shortly after sunset.
&&
.CLIMATE...
Issued at 325 AM EDT Tue Aug 26 2025
Record Low Temperatures...
Wed, Aug 27th Thu, Aug 28th
Rec (Yr) | FCST Rec (Yr) | FCST
SDF 51 (1946) | 54 51 (1986) | 55
FFT 41 (1896) | 47 47 (1896) | 50
LEX 49 (1968) | 49 50 (1986) | 51
BWG 47 (1945) | 51 49 (1986) | 55
Record Cold Max Temperatures...
Tues, Aug 26th
Rec (Yr) | FCST
FFT 73 (1944) | 76
&&
.LMK WATCHES/WARNINGS/ADVISORIES...
KY...None.
IN...None.
&&
$$
SHORT TERM...CSG
LONG TERM...CSG
AVIATION...CSG
CLIMATE...CSG
Source: LMK issues Area Forecast Discussion (AFD) at Aug 26, 3:26 AM EDT (https://mesonet.agron.iastate.edu/p.php?pid=202508260726-KLMK-FXUS63-AFDLMK)
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