228
FXUS63 KLMK 060734
AFDLMK

Area Forecast Discussion
National Weather Service Louisville KY
334 AM EDT Mon May 6 2024

.KEY MESSAGES...

*   Multiple rounds of showers and thunderstorms will move across
    the region today. One or two storms may produce gusty winds
    and/or small hail. Localized flooding is also possible.

*   Potential for multiple rounds of strong to severe storms Tuesday
    through Thursday. All severe hazards will be possible. There is
    some potential that a significant severe weather event could
    develop late Wednesday through early Thursday AM.

*   Localized flooding potential will exist where repeated rounds of
    heavy rainfall occur Wednesday into Thursday.

*   Cooler temperatures return by Friday and persist into the
    weekend.

&&

.SHORT TERM /THROUGH TONIGHT/...
Issued at 333 AM EDT Mon May 6 2024

Now through sunrise...

A NW-SE oriented band of showers and thunderstorms is lifting to the
north across the CWA at this hour. So far this morning, this band
has put down anywhere from 0.25-0.75" of rainfall, with 20-30 mph
wind gusts being observed along the leading edge. Would expect
shower/storm intensities to trend downward over the next hour or two
as convection is outrunning the area of >500 J/kg MUCAPE. This band
should lift through the area by just after sunrise, with an area of
showers and thunderstorms currently over Western KY/TN moving in
behind this leading band.

Today...

A mid-level shortwave trough currently analyzed extending from the
Ozark Plateau southeastward into the mid- and lower-Mississippi
Valley will lift northeastward into the Ohio and Tennessee Valleys.
A modest low-mid level SW jet will assist in advecting an
anomalously moist air mass into the region, with 00Z HREF PWAT
values ranging from 1.5-1.75" this afternoon. For reference, the
90th percentile PWAT climatology from BNA is ~1.4", with the daily
maximum ~1.7". The combination of ample moisture, large-scale ascent
thanks to mid-level CVA, and 1000-1500 J/kg MLCAPE will allow for
multiple rounds of showers and thunderstorms across the region.
Timing of individual waves of showers and storms will be difficult
if not impossible to anticipate more than a few hours in advance
given the primed environment and the lack of a well-defined forcing
boundary, although thunderstorms should be more likely this
afternoon thanks to diurnal destabilization. Any stronger storms
this afternoon could produce gusty winds and small hail, but
widespread severe convection is not expected given limited values of
DCAPE and relatively high freezing heights. HREF LPMM QPF values
indicate that localized swaths of 1-2+" of rain will be possible
where multiple heavy precipitation cores set up, so a localized
flooding threat will also be in place. Showers and storms should
subside after sunset tonight as instability decreases and the mid-
level trough moves off to the east.

Tonight...

There should be a relative lull in showers and storms overnight
tonight before our next round of storms arrives Tuesday morning. One
or two showers/storms may develop as a warm front/theta-E surge
lifts northward through the region. The potential exists for patchy
fog Tuesday morning, especially in locations which see heavier
amounts of rainfall today. Southerly winds will begin to increase
Tuesday morning, which will both limit overall fog potential as well
as keep temperatures mild, with lows only expected in the low-to-mid
60s Tuesday morning.

&&

.LONG TERM /TUESDAY THROUGH SUNDAY/...
Issued at 333 AM EDT Mon May 6 2024

============== Tuesday & Tuesday Night ==============

By Tuesday morning, showers and storms that formed in the Plains and
Midwest along a cold front will quickly race toward our region. This
activity will out-pace the surface cold front and begin to lose some
strength initially as it approaches our region... but low level
moisture advection out of south/southwest and surface heating will
lead to steepening low level lapse rates that will aid in some
destabilization. Models differ on how the convection will evolve
once it enters our region, and some of this will be impacted on the
time of day it arrives (later arrival would favor strong/severe
potential).

Environmental parameters favoring severe storms will begin to
reallly increase Tuesday afternoon into the overnight hours as the
surface cold front inches closer toward the region. Models prog an
axis of ~70 degree dewpoints to funnel in from the southwest that
will lead to moderately high levels of instability (2,000 J/KG
MUCAPE) in a weakly capped environment. Deep layer shear will also
increase as the front approaches. Two big questions that will impact
severe storm potential Tuesday are... (1) when will the first wave
of convection arrive (as well as depart), and (2) will subsequent
convection in the late afternoon/overnight period be able to
overcome a weak/subtle cap? Models don`t provide a clear, consistent
picture on this, unfortunately. For the late afternoon/overnight
convection, we will have some `triggers` to get convective
development going (approaching cold front, mesoscale boundaries left
behind from previous storms), and the weak/subtle capping should
result in said convection being largely discrete in nature. Assuming
storms do initiate and sustain themselves, given the shear profiles,
supercells would be the most likely storm mode overnight. All severe
weather hazards would be possible (tornadoes, large hail, damaging
straight line winds). The general hodograph shape is straight-line
through much of the troposphere, which would result in splitting
supercells that wouldn`t favor one specific type of mover
(left/right). With that being said, the hodographs do show some low
level clockwise curvature in the lowest 1 kilometer, so any right-
mover supercells that persist for some time would need to be watched
very closely as environmental Sig-Tor is fairly high (+3).

============== Wednesday & Thursday ==============

General model consensus (with some notable exceptions, more on that
in the next paragraph) have storms pushing out of the region
Wednesday morning while our frontal boundary will begins to lift
northward as a warm front. This would allow a period of
drying/clearing that would lead to destabilization again. A surface
low and cold front will begin approaching from the west ahead of an
upper level trough, and severe weather parameters ahead of these
features look even more concerning vs what we`ll deal with Tuesday
into Tuesday night. Additionally, stronger forcing will be in place
to develop more widespread storms (with both linear and discrete
storm modes possible). Severe storms will be capable of large hail,
damaging straight line winds, and tornadoes. Localized flood issues
may also arise given we`ll be dealing with multiple rounds of heavy
rain over a short timeframe. Models do have some minor differences
in the timing of convective development, but strong/severe storms
could start as early as Wednesday afternoon... with higher threats
Wednesday evening into the early morning hours Thursday as the front
approaches. This has the potential to be a significant severe
weather event.

As alluded to earlier, there are some model `outliers` that show
things evolving a bit differently on Wednesday. For example,
convection from Tuesday night storms could linger into Wednesday and
limit overall destabilization ahead of the next wave. Or, mesoscale
boundaries from previous convection may initiate showers/storms
early in the day on Wednesday and once again limit destabilization.
Or perhaps a combo of the two could unfold. These possible scenarios
limit confidence on a potentially significant severe weather episode
to some degree.

With all that being said, the Wednesday into Thursday morning setup
bears very close watching because of how impactful and significant
it could be. Should discrete supercells develop Wednesday evening
into early Thursday morning, environmental shear profiles strongly
favor right movers. Hodographs are quite scary looking and show
large, clockwise curvature in the lowest 1km with high amounts of
shear and helicity. Given other environmental parameters favoring
tornadic conditions, there is very concerning potential for a strong
(+EF2) tornado if we end up with an untapped warm sector ahead of
the front.

Those living within the region will want to keep up to date with the
latest forecasts 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 ==============

Much cooler conditions will filter in behind a cold front Friday
into the weekend. Doesn`t look like we stay entirely dry during this
timeframe as shortwaves pass through the region, but it shouldn`t be
a washout by any means either. There are some differences in how the
long range models handle upper level features, so for now will ride
with NBM PoPs for rain chances.

&&

.AVIATION /06Z TAFS THROUGH 12Z TUESDAY/...
Issued at 134 AM EDT Mon May 6 2024

A band of showers and embedded thunderstorms is moving from SW to NE
across the region at this hour. This area of rain will approach
SDF/HNB/LEX/RGA over the next 1-3 hours, with the precipitation
expected to be heavier at SDF and HNB, potentially resulting in
temporary MVFR/IFR visibilities. While the band is expected to
weaken as it moves northeast, amendments may be needed to add
thunder mention if the weakening trend is slower than expected.

Later this morning, an area of MVFR stratus is expected to move
across the region from the west. Model guidance has been struggling
with its timing as well as how low ceilings get within the area of
stratus, so forecast confidence remains low. Later today, several
waves of showers and embedded thunderstorms are expected to move
across the region. Timing of each individual wave will likely have
to be handled by short-fuse amendments, with reduced ceilings and
visibilities likely in the heaviest showers/storms. Outside of
showers and storms, winds should gradually increase out of the S/SW
late this morning and through the afternoon. Toward the end of the
forecast period, a return to VFR conditions is favored, though low
stratus may try to linger tonight at SDF/LEX/RGA.

&&

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

&&

$$

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