546
FXUS63 KLMK 050549
AFDLMK

Area Forecast Discussion
National Weather Service Louisville KY
149 AM EDT Wed Jun 5 2024

...Updated Aviation Discussion...

.KEY MESSAGES...

*   Scattered showers and storms likely today and Wednesday.  A few
    strong to severe storms are possible.  Gusty winds and
    torrential rainfall will be the main threats.

*   Drier weather and cooler temperatures are favored late week into
    the first half of this coming weekend.

&&

.UPDATE...
Issued at 742 PM EDT Tue Jun 4 2024

A weak upper level wave responsible for much of the rain and storm
activity earlier today is slowly lifting off to the northeast this
evening. Cooler temperatures from thunderstorm outflow as well as
subsidence aloft in the wake of the upper level wave have prevented
new convection from developing across western portions of the CWA
into western KY and southern IL/IN.

Another wave of rain showers and storms will be possible overnight
into early tomorrow morning ahead of another weak upper system.
Models vary on the extent of precip development with this next wave
but the current PoP coverage (20-40%, highest in our west) seems to
cover this uncertainty well.

&&

.SHORT TERM /THROUGH THIS AFTERNOON/...
Issued at 316 PM EDT Tue Jun 4 2024

Fairly widespread convection is in progress across much of central
Kentucky and far southern Indiana this afternoon.  Mesoscale
analysis shows abundant low-level moisture with PWATs in the 1.75 to
1.95 inch range.  MLCAPE values are modest with 750-1500 J/kg
available, but bulk wind shear values remain quite meager with only
20-25kts available.  Convection so far has been sub-severe with wind
gusts of around 40 mph in the strongest cells, along with torrential
rainfall (quick 1-1.5 inch amounts) and frequent lightning.

For the remainder of the afternoon, main area of convection will be
in areas along and east of the I-65 corridor.  North-south band of
convection just east of the I-65 corridor should continue to move
slowly north-northeast with additional scattered convection dotting
the landscape across east-central KY.  Best instability will likely
be out in the US 27/127 over to I-75 corridor where atmosphere
hasn`t been worked over yet.  A few strong/severe storms can`t be
ruled out, but most convection is likely to remain sub-severe with
wind gusts of 45-50 mph, torrential rainfall, and frequent
lightning.  Rainfall rates of 1-1.5 inch/hr will be possible in
spots and that may result in some isolated hydrologic issues in a
few spots.  Convection should diminish toward sunset as we loose
heating and the boundary layer begins to stabilize.

For the overnight period, most of the high resolution models show
mainly a dry period of weather.  However, with the low-level jet in
place (25-30kts) we could see some isolated convection across the
region.  However, overall confidence in high PoPs for the overnight
remains quite limited.  So for now, will just keep PoPs in the 30-
40% range.  Overnight lows will be mid-upper 60s.

Heading into Wednesday, an eastward moving cold front will push
toward the region during the day while a shortwave trough axis moves
through the Great Lakes region.  With the cold front approaching the
region in the afternoon, we should see a gradual increase in
convection across the area once again.  Uncertainty does exists here
as to how much cloud cover we`ll see during the morning and how fast
convection develops.  Should convection develop in the morning
hours, this could result in less instability being available.  Most
guidance shows about 1000-1500 J/kg of MLCAPE available with about
25-30 kts of bulk shear.  Better shear/instability looks to reside
to our north/northeast, but another bout of strong/severe storms
will be possible.  Main threats look to be torrential rainfall,
damaging winds, and frequent lightning.  Highs on the day will be in
the lower 80s.

&&

.LONG TERM /TONIGHT THROUGH TUESDAY/...
Issued at 316 PM EDT Tue Jun 4 2024

Transitional period Wed night and Thu as the main sfc cold front
pushes east of I-65 on Wednesday evening. Rain chances will taper
off from west to east toward midnight, with a cooler and less humid
air mass filtering in fairly quickly behind it.

Westerlies aloft pick up quickly Thursday as a closed low settles
over the Great Lakes as the anchor to broad eastern CONUS trofiness.
Will keep an eye on a weak upper wave which will likely be reflected
by a reinforcing sfc cold front. There`s a small chance this feature
could touch off isolated convection Thu afternoon, but it`s
sufficiently moisture-starved to keep the probabilities below 20% so
mention in the forecast.

Sfc ridging really wins out Thu night through at least the first
part of Saturday, with an anomalously dry Canadian air mass settling
in. Temps will run on the lower side of climo, with pleasant
dewpoints in the 50s to allow to temps to drop nicely at night.

Forecast confidence decreases late in the weekend with disturbances
taking shape over the Plains in both the northern and southern
stream. Old frontal boundary will be lingering to our south, and the
northern stream will have better dynamics, so there could be
multiple opportunities for precip to develop over one part or
another of the Ohio Valley. At this time we will keep POPs in the
low chance (20-30%) range, but it`s a very low confidence forecast.

&&

.AVIATION /06Z TAFS THROUGH 12Z THURSDAY/...
Issued at 149 AM EDT Wed Jun 5 2024

Tricky forecast cycle ahead as low ceilings, periods of showers and
storms, and some visibility restrictions could all come into play at
times. Early this morning, look for steady SSE to S winds with
variable cloudiness. A few instances of lower ceilings have appeared
at times, but are likely to be erratic through the early morning
hours. Also, can`t rule out some pre-dawn fog, but confidence is too
low to mention at this time. Later this morning, a better chance for
low MVFR ceilings is expected as a stratus deck briefly sets up,
however a return to VFR ceilings is expected again by early to mid
afternoon.

Do expect scattered showers and thunderstorms to develop later this
afternoon into the evening ahead of an approaching cold front. Given
a moist and unstable atmosphere, some locally heavy rain could
easily reduce vis briefly into the IFR range with any storm. Also
have a period of fairly strong S gradient winds between 10 and 15
mph, gusting up around 20-25 mph at times.

&&

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

&&

$$

UPDATE...DM
SHORT TERM...MJ
LONG TERM...RAS
AVIATION...BJS