577
FXUS63 KLMK 051036
AFDLMK

Area Forecast Discussion
National Weather Service Louisville KY
636 AM EDT Sun May 5 2024

.KEY MESSAGES...

*   Isolated showers and thunderstorms are possible today, mainly
    south and east of the Western KY/Bluegrass Parkways. More
    widespread rain chances return tonight 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.

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

&&

.UPDATE...
Issued at 433 AM EDT Sun May 5 2024

With multiple ASOS/AWOS sites now reporting below 2 SM visibility,
have gone ahead and added patchy fog to the forecast across the CWA
until 12Z. As usual, valleys and rural areas would have the greatest
chance to see fog, as well as areas which have received rain over
the past 6-12 hours. Updated products will be sent shortly.

&&

.SHORT TERM /THROUGH TONIGHT/...
Issued at 335 AM EDT Sun May 5 2024

Showers and thunderstorms have rolled across southern IN and
portions of western and central KY over the past 3-6 hours in
association with a weakening sfc cold front. At this hour, SPC
mesoanalysis places the front just east of I-65, although the front
loses definition the farther south you go. The front`s eastward
progression has been aided by convective outflows, as influence from
mid- and upper-level troughing has subsided. With instability
diminishing east of I-65, storms have largely fizzled over the
past hour or so, with little more than light rain showers
showing up on current radar. Between now and sunrise, a stray
rain shower cannot be ruled out given the front`s presence and
ample low-level moisture; however, would expect these showers to
be few and far between. The main thing to monitor between now
and sunrise is the potential development of patchy fog or low
stratus given light winds and ample low-level moisture. For
now, we`ll keep fog mention out of the forecast, but a
subsequent addition may be needed depending on obs trends.

Today, the aforementioned front is expected to wash out over the
Ohio Valley, leaving a NW-SE oriented low-level moisture gradient
across the region. Instability will vary in a similar manner, with
HREF mean SBCAPE values ranging from 1000-1500 J/kg south of the
Western KY/Bluegrass Parkways to less than 500 J/kg north of the
Ohio River. Accordingly, the greatest potential for regenerating
showers and storms late this morning and into the afternoon is south
and east of a line from Bowling Green to Frankfort. Any storms
which develop should be of the garden variety, as relatively
weak deep-layer shear remains over the region. Temperatures
this afternoon should reach into the upper 70s and lower 80s,
with conditions feeling much muggier the further south and east
you go.

Tonight, a mid-level shortwave disturbance will eject northeastward
from the mid-Mississippi Valley into the Ohio Valley. 850 mb theta-E
advection downstream of this wave should facilitate the
development of another wave of showers and thunderstorms, which
should begin to lift from SW-NE across the region between sunset
and midnight tonight. While several hi-res models show a band
of thunderstorms surging into the region on the leading edge of
this area of precipitation, the storms should arrive once
instability starts to decrease in the hours post-sunset. As
such, even though thunder is possible given elevated
instability, severe impacts are not expected at this time.

&&

.LONG TERM /MONDAY THROUGH SATURDAY/...
Issued at 335 AM EDT Sun May 5 2024

============== Monday ==============

Ongoing rain showers with perhaps some embedded storms in the rain
`shield` will continue to push through the region Monday ahead of a
compact shortwave trough. Elevated amounts of deep layer moisture
ahead of the trough will result in poor mid level lapse rates,
keeping instability levels fairly marginal through most of the day.
Model soundings do show low level lapse rates steepening some by the
afternoon in response to surface heating, helping to slightly
increase the instability in the atmosphere, but weak deep layer
shear will limit any sort of organized convective threat. Can`t rule
out an isolated strong wind gusts from a water-loaded downburst,
otherwise, no severe storms are expected.

============== Tuesday through Thursday ==============

A negatively tilted trough swinging from the Rockies into the
central Plains will transition into a deep, broad upper level low
(ULL) centered over the northern Plains by midweek. With weak/subtle
upper level ridging stretching from the Mid-Atlantic into the
Southeastern U.S., upper level flow over our region will shift to a
more active southwesterly direction. This will result in multiple
waves rotating around the base of the northern Plains ULL that will
likely impact our region, before portions of the ULL get swept up in
a trough by late Wednesday into Thursday.

Severe weather parameters ahead of some of these waves warrant
concern. By Tuesday evening, model soundings generally exhibit
moderate amounts of instability in a strongly sheared environment
supportive of organized convection. All severe weather hazards
(tornadoes, hail, damaging straight line winds) would be possible.
Localized flooding issues could also arise depending on QPF totals
toward the end of the week. Unsurprisingly, models have some minor
differences in the timing and evolution of these waves, but the best
chances for severe storms will likely come Wednesday afternoon into
Thursday AM as a surface low and cold front approach. Those living
within the region will want to keep up to date with the latest
forecast and make sure they have multiple ways to get warnings,
especially since these severe storms could come through in the
middle of the night when many are asleep.


============== Friday into the Weekend ==============

Cooler air behind the cold front will likely arrive by Friday and
persist into the weekend. Quite a few ensemble members point to
Saturday being one of the `coolest` days we`ve had in a while as
highs struggle to climb into the upper 60s and overnight lows fall
into the 40s.

&&

.AVIATION /12Z TAFS THROUGH 18Z MONDAY/...
Issued at 636 AM EDT Sun May 5 2024

Scattered areas of IFR/LIFR stratus will make the first 3-6 hours of
the current forecast very challenging, with ceilings expected to
bounce between categories at most if not all forecast sites. Later
this morning, there should be a gradual rise in ceilings as daytime
heating helps to mix out shallow moisture. This should allow all
forecast sites to return to VFR conditions by 16-18Z, with VFR
conditions expected to continue through the afternoon and early
evening hours. Winds will remain light today across the area, as a
decaying cold front will be stretched out across the region. Showers
and thunderstorms will be possible this afternoon at BWG, with
slightly lower confidence in SHRA/TSRA at LEX and RGA.

Tonight, another wave of more widespread showers and a few embedded
thunderstorms is expected to move across the region from SW to NE.
The heaviest showers and storms would be expected to bring reduced
visibilities and ceilings; however, confidence in timing is too low
to mention in the current forecast.

&&

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

&&

$$

UPDATE...CSG
SHORT TERM...CSG
LONG TERM...DM
AVIATION...CSG