LMK issues Area Forecast Discussion (AFD) at May 31, 9:35 PM EDT
883
FXUS63 KLMK 010135
AFDLMK
Area Forecast Discussion
National Weather Service Louisville KY
935 PM EDT Sat May 31 2025
.KEY MESSAGES...
* Isolated to widely scattered showers and storms expected this
evening. Locally strong wind gusts and hail will be possible
with the strongest storms.
* Weather to turn drier and warmer early next week.
* Active weather pattern to return by late next week with possible
strong/severe storms and heavy rainfall.
&&
.UPDATE...
Issued at 935 PM EDT Sat May 31 2025
So far this evening, convection has struggled to overcome poor mid-
level lapse rates, with convective cores not growing much taller
than 15-18 kft. However, in the past 30 minutes or so, a few cells
in Madison, Garrard, and Jessamine County have had the most robust
updrafts of the day so far, with 50 dBZ echoes reaching up to 17-18
kft. With -20 C levels around 22 kft, this is getting into the ball
park of where we could start to see some lightning, so wouldn't rule
out rumbles of thunder over the next few hours. This enhancement of
storms seems to be related to a ribbon of increasing sfc moisture
convergence on latest SPC mesoanalysis, as well as better
convergence throughout the sfc-850 mb layer as a subtle shortwave
slides across the region. Would expect the gusty wind threat with
these cells to be tempered by a strengthening nighttime sfc
inversion, though a stronger downdraft could get gusty winds down to
the surface over the next few hours.
Later this evening, the pool of low-level CAPE should diminish,
though a few showers may continue through the overnight hours.
Coverage should be isolated at best, with most of the showers
concentrated in the vicinity of the NW-SE oriented front which shows
up nicely in a band of clouds on latest nighttime microphysics
imagery.
&&
.SHORT TERM /THROUGH SUNDAY/...
Issued at 307 PM EDT Sat May 31 2025
Things are quiet across the CWA at this hour, and the big question
of the afternoon and evening will be whether or not we get some
showers and storms to spark along the back door cool front currently
set up across our CWA. The boundary in question appears to currently
be situated along an axis from KIMS to KIOB. Not much of a wind
shift (which is important, see below), but the drop off in dew
points most notably defines the boundary. Speaking of the wind
shift, we aren't currently seeing a whole lot of surface moisture
convergence along the boundary, which is likely due to the subtle
wind shift, however we are starting to get some slightly more
agitated cu in a narrow corridor associated with at least some
convergence and destabilization. We'll continue to monitor this
through the afternoon and into the evening as the boundary is
expected to make a little more progress southwestward into the
evening hours. If you're dew points fall off, you're out of the game
for the evening.
Anything that is able to fire will be in an environment
characterized by modest instability (500 J/KG of ML CAPE), but
fairly strong deep layer speed shear. DCAPE values should peak in
the 600-800 J/KG range, and given steep low level lapse rates (~8
C/KM), do think the isolated damaging wind gust threat could be
realized. Most likely place for this would be across our east
central CWA where Marginal Risk is currently placed, and where best
surface moisture convergence and instability will likely occur.
Overall, the timing of initiation is trending later, and this may
have something to do with the upper level smoke from Canadian
wildfires currently streaming overhead. Will note that mid level
lapse rates are pretty unimpressive, so a limiting factor to more
intense convection could be this if/when we do fire things off.
Any lingering convection dies off this evening along the boundary,
and it will stall somewhere between the NE half and NE third of the
CWA. The notable drop off in dew points will allow for cooler temps
across our NE CWA under good radiational cooling conditions. So,
we'll likely see some mid to upper 40s there. In contrast, our SW
CWA will likely stay in the mid to upper 50s on warm/moist side of
the boundary.
Sunday should be dry day for most, however we'll have to see where
the surface boundary hangs up as this will likely be the focal point
for additional scattered afternoon and evening thunderstorms.
Current progs are for this to be across our far southern CWA, where
another low threat of isolated damaging winds or hail could occur.
SPC may need to expand the Marginal Risk all the way across our
southern tier or so, but kinda have to wait and see where that
boundary will end up. Another notable temp gradient expected for
tomorrow with highs in the low to mid 70s NE, and in the upper 70s
and low 80s southwest.
&&
.LONG TERM /SUNDAY NIGHT THROUGH SATURDAY/...
Issued at 307 PM EDT Sat May 31 2025
Sunday Night - Wednesday...
The shortwave trough axis quickly slides east through New England,
with the surface boundary sliding even farther south of our CWA by
Sunday night. Surface high pressure builds into the area behind the
front, with upper ridging quickly taking hold of the pattern through
early to mid week. This will result in a dry stretch of weather with
increasing temperatures, especially Tuesday into Wednesday.
Overnight lows into Monday will still be fairly chilly given good
radiational cooling conditions. Most lows will bottom out in the low
to mid 50s, but perhaps a few of the typical cool spots sneak into
the upper 40s. Good diurnal ranges will follow to Monday afternoon
as we peak in the upper 70s and low 80s. Temps surge above normal
Tuesday and Wednesday with mid and upper 80s most common. A few
spots could touch 90 on Wednesday, especially if upper sky cover
holds off.
Wednesday Night through Saturday...
The upper ridge axis looks to slide east of us by later Wednesday,
with broader SW flow aloft trying to win influence into our region.
A cold front trailing from an eastern Canada surface low will
stretch from the Great Lakes down through the southern Plains, off
to our NW a bit. Convection will be ongoing ahead of this feature
Wednesday evening into Wednesday night, but it appears our
antecedent drier and more subsident airmass will mostly win out. As
a result, should only expect weakened convection in our western CWA
Wednesday night. By Thursday, a shortwave is expected to eject out
of the southern Plains toward the Great Lakes region, reinvigorating
convection along the stalled boundary outflow/frontal boundary
(likely over or just NW of our CWA). Thursday could very well be dry
and fairly hot (mid to upper 80s) again also as we get a bit of that
warm sector surge ahead of the surface, but really much depends on
how much influence we get from Wednesday night convection, if at all.
Could have some strong to severe storms later Thursday into Thursday
night ahead of the trailing cold front, especially with what should
be a fairly unstable airmass and an uptick in deep layer shear from
the shortwave trough. Something to watch.
Confidence lowers for Friday and Saturday as much will depend on
what happens with Thursday PM convection. Either we get a clean
sweep and the cold front/convectively reinforced boundary makes it
all the way through, or it hangs up and we linger chances for
showers and storms into the weekend. For now, we'll keep shower and
storm chances in the forecast with slightly cooler temps back in the
low and mid 80s.
&&
.AVIATION /00Z TAFS THROUGH 06Z MONDAY/...
Issued at 747 PM EDT Sat May 31 2025
A northwest to southeast oriented cold front extends across the
region this evening. Along the front, scattered showers have
developed, with most of the remaining shower activity expected to
avoid area terminals this evening. However, a stray shower,
especially along a line from SDF to RGA, cannot be ruled out
overnight, although probabilities are low. A prevailing mid-level
cloud deck should linger across the area tonight, with VFR
conditions and light winds expected.
On Sunday, clouds should gradually dissipate across SDF/LEX/RGA/HNB
as the front moves south. Additional diurnal cu are expected around
BWG tomorrow, and some of these may grow into SHRA/TSRA in the
afternoon, though the best chances will be to the south. VFR
conditions and light north winds are expected otherwise.
&&
.LMK WATCHES/WARNINGS/ADVISORIES...
KY...None.
IN...None.
&&
$$
UPDATE...CSG
SHORT TERM...BJS
LONG TERM...BJS
AVIATION...CSG
Source: LMK issues Area Forecast Discussion (AFD) at May 31, 9:35 PM EDT (https://mesonet.agron.iastate.edu/p.php?pid=202506010135-KLMK-FXUS63-AFDLMK)
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