387
FXUS63 KLMK 030552 AAB
AFDLMK

Area Forecast Discussion...UPDATED
National Weather Service Louisville KY
152 AM EDT Fri May 3 2024

.KEY MESSAGES...

*   Widespread showers and scattered thunderstorms Friday, mainly in
    the afternoon and evening. Brief heavy rain and lightning.

*   Probability of thunder is 15-25% in the morning, 40-50% in the
    afternoon.

*   Rain and storm chances decrease for Saturday, but forecast
    confidence is still low.

&&

.UPDATE...
Issued at 929 PM EDT Thu May 2 2024

Partly cloudy skies were noted across the region this evening.  Mid-
high level cloud cover continues to push in from the west.
Temperatures were in the upper 60s to the lower 70s across the
region. Regional radars show some light returns coming northeast out
of TN.  Not seeing much in the way of reports of rain at the
surface, likely due to the antecedent dry airmass in place.  The
atmosphere should continue to moisten during the remainder of the
evening and showers will become more widespread from west to east
overnight.  Current forecast has this well handled, and only minor
adjustments to the weather elements were required.

&&

.SHORT TERM /THROUGH FRIDAY/...
Issued at 327 PM EDT Thu May 2 2024

========== Tonight and Friday Morning ==========

Dry weather will continue for this evening and tonight, but clouds
will be on the increase as our next system approaches. A mid-level
wave will eject out of the ArkLaTex region and track northeastward
into the lower Ohio Valley tonight, resulting in a moisture
advection axis ahead of an extensive cold front associated with a
sfc low that will be over the Great Lakes. We should begin to see
radar returns after midnight, but dry low levels will likely delay
precip making it to the ground until after 06z. A few isolated
embedded rumbles of thunder may be possible overnight, but
instability will be very limited and elevated above the nocturnal
inversion.

Shower activity will continue to spread eastward through the pre-
dawn hours, and may peak in overall coverage between 10-15z as our
PWATs maximize for the day around 1.5". PW values this high would be
among the daily max for sounding climatology from BNA. Model
soundings do show some limited instability in the morning hours
after sunrise as well, so some embedded thunder will be possible
then too. Overall though, the morning appears to be a soaking rain
with an isolated thunder chance. The probability of thunder in the
morning hours will be between 15-25% chance.


========== Friday Afternoon and Thunderstorm Potential ==========

By the early afternoon hours, the cold front will be approaching the
I-65 corridor. With numerous to widespread showers in the morning,
skycover guidance does not suggest much clearing out for the
afternoon, which is good news for keeping severe potential low.
However, temps will still warm into the low to mid 70s with
dewpoints in the mid 60s, leading to some sfc based instability.

According to our DESI tool, 70% of HREF members support SBCAPE
values greater than 500 J/kg tomorrow afternoon north of the
Kentucky Parkways, and 40% of members above 750 J/kg. After 18z, the
CAMs begin to show more a convective nature to precip along or just
ahead of the front as the marginal instability is realized.
Fortunately, soundings show very weak flow through the column, so
there won`t be much shear for storms to work with. Regardless of the
weak flow, our probability of thunder increases to 40-50% during the
afternoon hours with scattered garden variety thunderstorm likely.

&&

.LONG TERM /FRIDAY NIGHT THROUGH THURSDAY/...
Issued at 327 PM EDT Thu May 2 2024

Synopsis...Quasi-stationary weather pattern is expected during the
medium-range period as mid-level ridging extends roughly across the
East CONUS and a couple of northern-stream, shortwave troughs swing
by the western and central portions of the country. The resultant
southwesterly mid-level flow will drag southern-stream, mid-level
vorticity waves from the South towards the Lower Ohio Valley,
promoting daily rain/storm chances this weekend into next next. A
low risk of strong to severe storms cannot be ruled out during the
Tuesday/Wednesday timeframe.

Model Evaluation/Confidence...Overall, forecast confidence for
Saturday remains relatively low with some improvement regarding the
evolution of the second northern-stream trough across the central US
early next week. For Saturday, the wettest models (NAM-12 and some
runs of the GFS, ECMWF, and UKMET) depict stronger, convectively-
enhanced shortwave energy from earlier convection in the Deep South
moving further west and north while the dry/drier model solutions
represent a weaker wave quickly ejecting to the east. One thing to
notice is that CAM guidance, including NAM 3km, support decreasing
shower activity in the afternoon with perhaps isolated coverage. For
next week, global guidance has started to converge on a similar
output regarding the position of trough axis with some differences
in the timing and structure of embedded shortwave energy. Given the
aforementioned trend and continuing severe weather probabilities
highlighted in the CSU and NCAR ML algorithms, a low risk of strong
to severe weather is still on the table for Tuesday and/or
Wednesday.

Fri Night - Saturday...Weak frontal boundary will slowly translate
through the forecast area overnight while slowing down as it
approaches south-central Kentucky in the morning hours. Uncertainty
in the convective evolution further south will play a key role in
the precipitation and storm chances during the day on Saturday,
especially in the afternoon. Should a wetter solution materializes,
mid-level shortwave forcing along the stalled frontal boundary will
enhanced storm probability and coverage. Taking into account a
consensus of the 12Z model data, decided to support a dry solution
reflecting decreasing rain chances towards the afternoon with a 20-
30 percent chance of thunder as sufficient BL moisture and
convective temperatures (amid some residual boundary interaction)
could force isolated convection. Lightning and brief heavy rainfall
are the main hazards with any storm. Last but not least, there will
be a renewed chance of showers and storms late in the afternoon and
early evening as another frontal boundary approaches from the NW.

Sunday - Next Week...Daily rain and possibly storm chances will
continue from Sunday and onwards as enough instability combines with
southern-stream shortwave forcing. Best chance for strong, organized
convection is still anticipated for Tuesday and Wednesday as the
better dynamics and stronger mid-level winds spread over the
forecast area. Based on available guidance, there is a low chance of
severe weather without ruling out possible minor flooding if
unsettled weather extends during several days.

&&

.AVIATION /06Z TAFS THROUGH 12Z SATURDAY/...
Issued at 151 AM EDT Fri May 3 2024

First band of showers is just getting into BWG and approaching SDF,
but with abundant mid-level dry air we aren`t seeing any
restrictions to cig/vis. Expect to remain VFR through the overnight
period with light rain showers, though it could rain hard enough at
some point to briefly drop vis into MVFR.

A more stout band of precip moves through from mid-morning through
early afternoon, with MVFR cig/vis, but not really dropping below
2000 feet except in the heaviest of showers. Instability looks
limited so we won`t mention any thunder except for a VCTS mention at
SDF during the earlier part of the afternoon.

Late afternoon into the evening could still see some isolated
showers, but probabilities not high enough to include in the TAFs.
Winds from the SE overnight will try to settle into a SSW direction
after daybreak, then more easterly later in the day behind the main
band of showers. Speeds less than 10 kt. Overall forecast confidence
is medium.

&&

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

&&

$$

UPDATE...MJ
SHORT TERM...CJP
LONG TERM...ALL
AVIATION...RAS