LMK issues Area Forecast Discussion (AFD) at May 1, 1:29 PM EDT088
FXUS63 KLMK 011729
AFDLMK
Area Forecast Discussion
National Weather Service Louisville KY
129 PM EDT Thu May 1 2025
.KEY MESSAGES...
* Scattered strong to possibly severe thunderstorms are possible
this afternoon and evening, mainly east of Interstate 65.
* Scattered showers and thunderstorms are expected once again
Friday afternoon and evening. A few strong or marginally severe
storms are possible, with gusty winds and small hail being the
primary hazards.
* Increasing likelihood of showers and cooler temperatures over the
weekend. A few non-severe thunderstorms are possible.
&&
.UPDATE...
Issued at 1209 PM EDT Thu May 1 2025
Subtle sfc trof currently extends SSE from low pressure lifting
toward Lake Michigan, and has touched off a narrow band of showers
with a few thunderstorms this morning. Said band of showers is
currently aligned from near Madison, IN through the Louisville Metro
to near Bowling Green, KY, but all the lightning activity has
remained over Indiana.
SPC mesoanalysis suggests the more favorable environment is to our
north and east, up toward Cincinnati, and the behavior of these
showers and storms backs that up. The window for strong to severe
storms will be opening over the next couple of hours, especially
near the I-75 corridor, as we continue to destabilize. If storms
continue to develop near the I-65 corridor and move NE into this
environment, that could fuel some severe wind producers. However,
mid-level lapse rates are quite modest, so not as sold on the hail
threat.
It's still early in the afternoon, which could leave time for the
atmosphere to recover ahead of storms on the main cold front in the
late afternoon or early evening. Believe this is still a lesser
threat as slight veering of sfc winds will limit the shear by this
time. Overall will continue to message the existing Slight Risk,
keying more on the early/mid-afternoon hours east of Interstate 65.
Outside of storms we are already seeing 30-35 mph wind gusts, which
could slack off a bit after the passage of the weak sfc trof. Still
expect some recovery as we mix out this afternoon, which we will
continue to highlight in the Hazardous Weather Outlook.
&&
.SHORT TERM /THROUGH TONIGHT/...
Issued at 348 AM EDT Thu May 1 2025
Today, a shortwave embedded in a larger upper trough will push a
surface low from northern Illinois into the Great Lakes region. This
will increase the surface pressure gradient across the Lower Ohio
Valley as the surface low pushes into the high pressure over the
Southeast, keeping south-southwest winds gusting to 25-30 mph
throughout southern Indiana and central Kentucky. It will also usher
moisture with precipitable water values remaining near 1.5 until
they begin dropping to around an inch through the evening hours.
We have a line of leftover showers working east towards the CWA
currently. In the coming hours this precipitation will likely
continue fading before new convection is expected to develop around
midday. It appears the strongest thunderstorms will be east of
Interstate 65 (in an area that could see some extra sunshine), and
like yesterday, believe there is a marginal chance for severe
weather. With the gradient winds, some storms could get some
stronger gusts to the ground with steep low level lapse rates, but
believe the main threat will be hail in any of the stronger storms.
With deep layer 0-6 km shear being kind of weak, around 30 knots,
and many model soundings showing veering winds at the surface,
believe the supercell and tornado threat is pretty low. Highs are
expected to reach into the mid 70s to low 80s.
Behind the broken wide line of activity, expecting mostly dry
conditions, and by tonight, all but possibly a few isolated showers
will be east of the CWA. Skies will likely become more broken. Winds
will ease some but will continue to gust to 10-15 mph for most of
the night. Lows are expected to drop into the upper 50s to low 60s.
&&
.LONG TERM /FRIDAY THROUGH WEDNESDAY/...
Issued at 348 AM EDT Thu May 1 2025
Friday and Friday Night...
Another unsettled day looks likely on Friday across the region;
however, the magnitude of the severe thunderstorm potential is still
fairly uncertain. At the beginning of the period, upper level height
falls are expected across the Plains as troughing amplifies to our
west. At the same time, the leading shortwave disturbance which will
at least partially force storms this afternoon and evening will be
moving across the lower Great Lakes, with an associated sfc low and
trailing cold front expected just ahead of the upper wave.
As this leading cold front sinks into the Ohio Valley from the NW,
lower sfc dewpoints will begin to reduce instability from NW to SE.
The cold front is expected to slow down as it lays out parallel to
the upper-level flow Friday afternoon, with an instability gradient
likely sitting over the region Friday afternoon and evening. South
and east of the gradient, short-range guidance shows around 1500-
2000 J/kg of MLCAPE, and given convective temperatures in the mid
70s, it is likely that scattered showers and thunderstorms will
develop Friday afternoon. Initially, wind shear will be fairly weak
(15-20 kt) as stronger flow aloft remains to the north and west. As
the trough axis moves closer to the area Friday evening, there will
be greater potential for organized storms, and the parameter space
would support a few storms with strong-to-severe wind gusts and/or
hail. Scattered showers and storms will likely continue into Friday
night as the secondary upper wave and associated sfc disturbances
moves across the region, though the severe potential should
gradually diminish.
In addition to the uncertainty with where the meso- and synoptic-
scale boundaries and the instability gradient sets up, given the
broad warm sector south of the front extending all the way back into
the southern Plains, convection to our west Friday morning across
OK/TX/AR could significantly alter our strong storm potential Friday
evening. Considering all of these things, confidence in severe storms
on Friday/Friday night is low-to-medium at best. The greatest
likelihood for severe should be along and south of the western
KY/Bluegrass Parkways.
Saturday through Sunday Night...
The likelihood of rain showers continues to increase for Saturday,
with rain chances continuing throughout the weekend. While several
GEFS members in previous runs showed an upper low hanging over the
region like the Euro and Canadian solutions, the 18Z and 00Z GFS
deterministic runs are now following suit, with model convergence
beginning to take place. As a result, richer moisture with elevated
PW values are expected to linger in the vicinity of the upper low
across the Ohio Valley.
With that being said, neither Saturday or Sunday will be a complete
washout, with isolated to scattered coverage of rain showers
expected at this time. There is just enough instability hanging
around to carry a mention of thunderstorms in the forecast; however,
lightning should be much more isolated over the weekend than today
or tomorrow. With increased cloud cover and a minimum in heights
aloft overhead, temperatures are expected to cool down over the
weekend. While the current forecast calls for highs in the 60s both
Saturday and Sunday, there is around a 25% chance that temperatures
don't reach 60 degrees on Sunday, and confidence in exact
temperatures is also fairly low at this time. Nighttime temperatures
will be cooler as well, and while increased moisture should limit
diurnal ranges, still expect lows Saturday and Sunday night in the
upper 40s and lower 50s.
Early-to-Mid Next Week...
How the upper low evolves over the region will control many
aspThis does not represent a change to the previous forecast. ects
of the forecast for the first half of next week. There is still
quite a bit of spread in how quick the upper trough ejects out,
with some guidance showing a brief Rex Block setting up early
next week, bringing the upper flow pattern to a halt for 36-48
hours. If the upper low is slower to eject out, we can expect
continued diurnally- driven chances for scattered rain showers
and a few garden-variety thunderstorms, with cooler temperatures
likely in the 60s for highs. A more progressive pattern with
the upper low lifting out of the region Sunday into Monday would
bring a warming trend through the first half of next week
(warming at least into the mid-to-upper 70s), with lower rain
chances in general. At this time, there are no strong signals
for severe weather or flooding early-to-mid next week, though
unsettled weather with relatively minor impacts would be
expected with the upper low overhead.
&&
.AVIATION /18Z TAFS THROUGH 00Z SATURDAY/...
Issued at 129 PM EDT Thu May 1 2025
Broken line of showers will approach LEX and RGA shortly after the
valid time of the TAF, and could intensify enough to warrant a
period of TS/CB mentions this afternoon. Otherwise could see some
lower stratus this afternoon, including at SDF and BWG, but not
enough for a MVFR cig. Wind gusts from the SW back off slightly, but
still expect plenty of gusts in the 20-25 kt range.
Convection at LEX and RGA should dissipate before sunset, with mid-
level debris lingering this evening. SDF and BWG should look for
cirrus ceilings overnight, with light SSW winds once gusts diminish
around sunset. Another boundary Fri morning will shift winds to WSW
by 14-15Z with a strato-cu deck coming in, albeit just barely VFR.
New convection on Friday should hold off until later in the
afternoon, and confidence was not sufficient to include it in the
SDF planning period.
&&
.LMK WATCHES/WARNINGS/ADVISORIES...
KY...None.
IN...None.
&&
$$
UPDATE...RAS
SHORT TERM...KDW
LONG TERM...CSG
AVIATION...RAS
Source:
LMK issues Area Forecast Discussion (AFD) at May 1, 1:29 PM EDT---------------
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