599
FXUS63 KLMK 222316
AFDLMK

Area Forecast Discussion
National Weather Service Louisville KY
716 PM EDT Thu May 22 2025

...Updated Aviation Discussion...

.KEY MESSAGES...

* Well below normal temperatures are expected through the first part
  of Memorial Day weekend.

* Continuing to monitor a low pressure system late weekend into
  early next week that will bring rounds of showers and
  thunderstorms. 1 to 2 inches of rain with locally higher amounts
  is currently forecast.

&&

.SHORT TERM /THROUGH FRIDAY/...
Issued at 317 PM EDT Thu May 22 2025

It has been a breezy day across the region, with KY Mesonet obs
showing the peak wind gusts across the state in the 25-35 mph range.
This is in response to steep low level lapse rates and mixing up
into a 30kt LLJ overhead. Temps range quite a bit from north to
south across the area, mainly thanks to the cloud cover. More cloud
cover has kept temps in the 60s north of the Parkways, but the
southern half of the CWA has reached the low 70s under sunny
skycover. Regardless, the breezy NW winds have helped keep temps
below normal today anyway. A few isolated light showers are noted in
our northeastern CWA, which is being driven by a weak shortwave
passing through with mid-level vorticity supplementing the lapse
rates. We`ll have a chance for some isolated showers in our
northeast through the rest of the afternoon, but as we lose the
steep lapse rates, those PoPs will diminish for the evening hours.
This will also result in our winds relaxing by 00z or so.

For tonight, clouds could hang on for the first half of the night as
the mid-level wave departs, but should have clearer skycover after
06z or so. Winds will be light, and with the less cloud cover, temps
could get chilly for this time of year. Overnight lows in the 40s if
forecast, with the southern IN and Bluegrass regions expected to be
the cooler spots in the low 40s.

Dry weather and cool continues tomorrow as sfc high pressure sits
overhead and NW flow aloft. This will promote sfc highs only
reaching the upper 60s, with perhaps a few locations hitting 70.
Regardless, the NW flow will help keep temps below normal for this
time of May. After a clear morning, should have some diurnal cu
blossom across the region in the afternoon. With dewpoints in the
40s, should be a pretty nice day.

&&

.LONG TERM /FRIDAY NIGHT THROUGH THURSDAY/...
Issued at 317 PM EDT Thu May 22 2025

===== Friday Night - Saturday Night =====

NW flow aloft will be over the region for the beginning of the
period, with the large upper low over New England, and sfc high
pressure across the Ohio Valley. This will influence cooler temps as
we head into the weekend, and mostly dry conditions.

Temps start out chilly Saturday morning, with morning lows in the
40s for most. Clouds will be increasing to our west Saturday
morning, which may play into keeping some of those Saturday morning
lows closer to 50 in our far western CWA. A weak perturbation in the
mid-level flow looks to ride through the NW flow, and will be the
driving force for a cluster of showers and storms to sweep across
Missouri, Arkansas, Tennessee, and western Kentucky and along the
warm front located well to our southwest. Will carry a 20-30% chance
for light rain across south-central KY for Saturday morning and
afternoon, though better chances will be across far western Kentucky
and Tennessee where the better moisture will be. Most of our
forecast area will remain dry on Saturday, with increasing cloud
cover and temps peaking around 70 in the afternoon.

Overcast skycover by Saturday night will trend to milder temps for
Saturday night, with rain chances expected to expand northward as
the aforementioned warm front pushes northward into the TN Valley.


===== Sunday - Monday Night =====

The second half of the holiday weekend appears to be more active
with precip chances, thanks to the warm front stalling across
Tennessee for Sunday and Monday. We`ll be locate do one the cool
side of the warm front, with numerous to widespread showers expected
for Sunday and Monday as isentropic ascent over the warm front leads
to better rain chances on the cool side of the boundary. Models
continue to indicate a lack of instability, which given the cooler
temps, seem to agree. Best chance for any embedded thunder should be
across south-central KY on both days, which slightly warmer temps
and higher dewpoints will be located. The CSU ML does have a low-end
prob for severe on Sunday across the southern half of the area, but
not overly concerned for severe threat. Model soundings show meager
shear parameters in the lower levels both days, though slightly
better deep layer shear for Monday. It`s something to just keep an
eye on for now.

The bigger concern could be the heavy rain potential, with PWATs
possibly exceeding 1.4-1.5" on Sunday and surging to 1.7-1.8" on
Monday. Monday`s PWAT values could be among the max in the sounding
database from BNA. The Sunday-Monday time frame along could bring
upwards to 2.00-2.25" of rain for some along the KY/TN state line, 1-
2" south of the Parkways. This will bring the Green River basin into
the cross hairs again. As mentioned in the previous discussion,
we`re at the time of year where we can handle some rainfall,
especially after a few days of dry leading up to it. That being
said, the river basin will already be running high, so it could at
least bring a river flood threat along with some localized nuisance
flooding concerns down there.


===== Tuesday - Wednesday =====

The 12Z global deterministic trends have delayed when a sfc low will
pass through, and the EURO/GFS/GDPS agree with some time on Tuesday,
though still have disagreements on placement and time of day.
Regardless, it appears the sfc low will keep cool and wet conditions
going into the mid-week. Look for highs mostly in the low and mid
70s, however the north will have the best shot at staying confined
to the 60s.

&&

.AVIATION /00Z TAFS THROUGH 06Z SATURDAY/...
Issued at 715 PM EDT Thu May 22 2025

VFR conditions are expected through the current forecast period. A
low pressure system northeast of the area will slowly pull out of
the region tonight into tomorrow. This should allow winds to
decrease overnight and become light and variable at most sites.
Through 02-03Z, a few light rain showers will approach SDF and LEX.
Expected coverage and impacts is too low to carry SHRA in the
forecast; however, a brief shower is possible this evening. Later
tonight, the stratus layer should begin to break up, with mostly
clear skies continuing into Friday morning. Tomorrow, winds will be
lighter than today out of the W/NW, with a 6-8 kft stratocu deck
expected to develop around midday.

&&

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

&&

$$

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