107
FXUS63 KLMK 041949
AFDLMK

Area Forecast Discussion
National Weather Service Louisville KY
349 PM EDT Sat May 4 2024

.KEY MESSAGES...

*   Isolated to scattered showers and thunderstorms are forecast
    this afternoon. Slow moving storm motion and moderate to heavy
    rain expected with any storm.

*   Isolated showers and thunderstorms are expected on Sunday before
    widespread rain chances return Sunday night into Monday.

*   Potential for multiple rounds of strong to severe storms next
    Tuesday through Thursday. Although confidence in timing remains
    low, all severe hazards will be possible.

*   Elevated flooding potential will exist where repeated rounds of
    heavy rainfall occur next week.

&&

.SHORT TERM /THROUGH TONIGHT/...
Issued at 348 PM EDT Sat May 4 2024

========== Rest of This Afternoon ==========

Fairly moist atmosphere over the area, with precipitable waters
around the 90th percentile. Storms have developed in this humid
airmass, with best convective development where the MLCAPE per SPC
mesoanalysis is over 1000 J/kg. Louisville ACARS most recent
sounding shows a couple of small inversions, at ~800 mb and 700 mb,
which may be inhibiting deeper development over the city. HRRR
sounding forecast represents these inversions well and keep them in
place through the afternoon. Thus will keep the best chances for
storms east of the i-65 corridor.

========== Tonight ==========

Showers/Storms from the afternoon should steadily decrease this
evening. Cannot rule out some isolated development in the moist
airmass. Should be another mild night as dewpoints remain elevated
and lows by Sunday morning should be in the low 60s. Model progs
keep clouds around overnight and thicken/lower them during the
morning hours.

========== Sunday ===========

How long those low clouds hang around in the morning and early
afternoon hours will have a direct influence on afternoon
convection. Have bumped PoPs down a touch, with the better chances
south and east of a Russellville to Bardstown to Frankfort line.
Some CAM`s have gone dry for the afternoon, but given potential for
some breaks in clouds and precipitable waters still above normal,
though not as much, feel prudent to keep in some storm chances.
Temperatures should rise into the 80`s for most places.

&&

.LONG TERM /SUNDAY THROUGH SATURDAY/...
Issued at 348 PM EDT Sat May 4 2024

Synopsis...A multi-day severe weather episode will be possible by
the middle of the next week as an upper-level trough evolves and
amplifies over the central US and eastern CONUS upper ridge axis
transitions from the Great Lakes to the Mid Atlantic/Southeast US.
The timing for best chances of severe weather will be tied to the
progression of periodic, mid-level shortwave troughs rounding the
base of the large through and embedded upper low. Eventually,
continuous ejection of strong shortwave troughs will carry the main
upper low energy towards the eastern CONUS while deeply amplifying
once again due to further reinforcement from upstream Canadian
troughing.

Model Evaluation/Confidence...Confidence in large-scale features
continue to be medium to high with expected decreasing confidence in
timing and intensity of shortwaves ejecting ahead of the main upper
low. The timing differences in incoming strong mid-level forcing
could lead to great variability in convective intensity, coverage,
and maintenance based on a potential onset time around sunset (both
Tuesday and Wednesday) and the resultant distribution/amount of
available daytime instability. Also, it is too early to pinpoint
specifics about meso features that would certainly play an important
role in initiation convection, such as the position of the residual
outflow boundary on Tuesday afternoon/evening or the effect of
previous convection and the interaction with approaching frontal
wave on Wednesday. In any case, machine learning derived guidance
has been consistently highlighting elevated probabilities of severe
weather across the region for Tuesday and Wednesday, with a recent
trend for higher probabilities for Wednesday.

Sun Night - Monday...Increased shower activity along with some
isolated storms are likely Sun night into Monday morning as a
southern-stream shortwave trough moves from the southern Plains to
the lower Ohio Valley. A combination of increased moisture advection
and potentially slow storm motions/backbuilding could result in
isolated accumulations over half an inch or more. On the other hand,
warming mid-level temperatures and decreasing instability will limit
thunder chances and promote more of a low-centroid type of storms.
The vorticity wave will push a frontal wave stalled across the
region to the north, so will keep mentioning reduced PoPs during the
afternoon and evening.

Tuesday - Thursday...Daily severe weather chances appear to focus
around sunset and overnight every day. For Tuesday, a weakening cold
front will move into the forecast area Tuesday morning and early
afternoon and although there will be an increase in showers during
the morning, it seems that forcing will subside substantially to
reinvigorate convection. Nonetheless, the residual outflow boundary
will establish somewhere along the Wabash Valley and into central
Indiana, which could be the mesoscale focus for convection late in
the afternoon and early evening as a surface low (ejecting across
the Upper Midwest) drags a cold front to the southeast. Based on
current guidance, highest severe probs will be close to the outflow
boundary further north with a decreasing trend in convective
intensity as it approaches southern Indiana and north-central
Kentucky. On the other hand, Wednesday looks more threatening as the
front will be located closer to the forecast area and the second mid-
level shortwave energy brings a surface low across the Wabash Valley
and IN. Therefore, forcing will be significantly higher amid a
moderately high unstable warm sector and sufficient deep-layer shear
for organized, spinning updrafts. All severe hazards are on the
table as well as a risk of flooding given the possibility of
repeated rounds of heavy rainfall.

Friday - Sunday...Amplifying trough over the eastern CONUS will push
the cold frontal and associated unsettled weather activity south of
the forecast area. As a result, rain and storm chances will decrease
during the day on Friday with breezy NW winds and persistent low-
level cloud cover the rest of the day. Temperatures during the
weekend seems to fall near or slightly below normal under light NW
breeze and partly to mostly skies. A more stable airmass will
indicate dry conditions for Saturday and Sunday.

&&

.AVIATION /18Z TAFS THROUGH 00Z MONDAY/...
Issued at 348 PM EDT Sat May 4 2024

Plenty of moisture around for early May and with daytime heating,
seeing some popup showers/storms. Focus for storm development seems
to be south of the I-64 corridor so far, but anticipate
KBWG/KLEX/KRGA to see additional storms in their vicinity. Cannot
rule out KSDF, but for now will lean on the optimistic side. Storm
chances should taper off quickly with loss of heating, but expecting
to see some low stratus development overnight and into Sunday
morning. Cannot rule out IFR conditions along the I-64 corridor and
KRGA, but will go for MVFR thresholds for now, even below 2 kft at
the KLEX/KHNB/KRGA terminals.

&&

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

&&

$$

SHORT TERM...RJS
LONG TERM...ALL
AVIATION...RJS