684
FXUS63 KLMK 032347
AFDLMK

Area Forecast Discussion
National Weather Service Louisville KY
747 PM EDT Wed Jul 3 2024

...Updated Aviation Discussion...

.KEY MESSAGES...

*   Heat index values this afternoon will range from near 100 in the
    Bluegrass region to 105 or higher west of Interstate 65.

*   Scattered thunderstorms this evening will be capable of strong
    gusty winds and torrential downpours. Overnight the severe
    threat will diminish but heavy downpours remain possible, which
    could result in localized flash flooding.

*   Unsettled weather will continue through Friday with daily
    chances of showers/storms. Isolated damaging wind gusts,
    torrential rainfall, and lightning will be the primary hazards.

&&

.MESOSCALE...
Issued at 746 PM EDT Wed Jul 3 2024

The Severe warned storm in Dubois county rapidly intensified on a
boundary intersection between the effective frontal boundary draped
WSW to ENE across southern IN, and a differential heating boundary
created by the upper cirrus shield. SPC mesoanalysis showed good
surface moisture convergence (10 g/kg) ahead of the explosive
development, combined with visible satellite imagery confirming
congested cumulus in the area. Overall deep layer shear around 30
knots, boundary interaction enhancing low level SRH, and the strong
updraft helped the storm exhibit some brief supercellular
characteristics. The good news is that LCLs are currently around
1250m, which is pretty high and not as favorable for tornadic
activity, and the the overall environment (outside of localized
enhancement from boundary interaction) isn`t favorable for tornadoes
anyway.

The storm has since shown signs of pretty strong outflow, so
continue to think that damaging winds and torrential rains will be
the main threats. Keeping a close eye on the boundaries, and their
effect on storm mode, but not overly concerned outside of the
microburst/localized flooding threat at the moment. It is
interesting to note that the western side of the differential
heating boundary mentioned above is also a clear marker between the
higher DCAPE airmass (better mixing), and the slightly less
favorable airmass under the cirrus shield.

&&

.SHORT TERM /THROUGH THURSDAY/...
Issued at 328 PM EDT Wed Jul 3 2024

Low-confidence forecast in a very warm, muggy, and boundary-rich
environment.  Plenty of low-level instability, but very weak mid-
level lapse rates will limit convection to that which can find
forcing.

We do have a cold front draped across central Illinois, with
lingering outflow boundaries from earlier activity in southern
Illinois and central Indiana. Hi-res models light up these features
starting around 22-23Z, with the best chances over southern Indiana.
Will also be closely watching the differential heating along the
southern edge of the cirrus shield, which is draped close to the
Cumberland Parkway in south-central Kentucky.

Given the steep low-level lapse rates and PWAT values over 2 inches,
we could still see a few strong to marginally severe pulse storms,
with locally gusty winds and torrential downpours. Best coverage is
likely to be in southern Indiana and north-central Kentucky.

If storms organize over southern Illinois, that could yield another
wave of storms late tonight into Thursday morning. Main threat will
be heavy rainfall, given PWATs still over 2 inches and tall/skinny
CAPE profiles, and localized flash flooding is possible anywhere
that heavy rain can regenerate. WPC has a Slight Risk for excessive
rainfall just on either side of the Ohio River.

Depending on how long precip continues into Thursday morning, it
will likely limit afternoon temperatures and storm intensity. Look
for mainly hit-and-miss convection on Thursday afternoon, as the
environment is still very moist and lingering boundaries could focus
storm development.

&&

.LONG TERM /THURSDAY NIGHT THROUGH WEDNESDAY/...
Issued at 328 PM EDT Wed Jul 3 2024

Thursday Night - Friday Night...

Low pressure will move through the Midwest bringing a cold front
through the Ohio Valley by Saturday morning. With deep troughing
associated with the system, CVA, and a weak, but well-positioned
upper-level jet dynamics, showers and storms will be move through
along and ahead of this front on Friday. Strong storms and storm
coverage is dependent on preceding convective activity today and
Thursday. If the environment recovers from preceding convection,
present shear and ample moisture will allow for a marginal risk of
severe storms due to potential for gusty to damaging winds and heavy
downpours. Flash flooding will be possible as the atmosphere is near
max climatology for PWATs in the 2.1-2.3 inch range and dew points
in the mid 70s. As the cold front moves through Friday night, drier
and cooler weather will build into the region.

Additionally, Thursday Night (Independence Day) should be mostly
dry. A nocturnal inversion will quickly settle into the region around
sunset. Firework smoke from 4th of July celebrations will be easily
trapped under the inversion and skies will become smokey through
Thursday night.

Weekend...

Drier and near normal conditions will stick around through the
weekend. High in the mid-upper 80s, dew points in the low-mid 60s,
and a light breeze will bring pleasant summer conditions. High
pressure over the region will keep mostly sunny skies with scattered
diurnal Cu formation in the afternoon.

Early Next Week...

Deep troughing will build over the central CONUS and high pressure
will move off to the east. Southwesterly flow and moisture will
return to the region. Shower and storm chances increased Tuesday as
a the trough swings through the upper Midwest. Temperatures will
remain near normal with dew points in the low 70s.

&&

.AVIATION /00Z TAFS THROUGH 06Z FRIDAY/...
Issued at 746 PM EDT Wed Jul 3 2024

A line of thunderstorms is currently oriented WSW to ENE roughly
along the Ohio River at this hour. Expect rapidly improving
conditions at HNB at the top of the hour, and conversely expect
rapidly deteriorating conditions at SDF at the same time. Expect SDF
to experience off and on TSRA for the next couple of hours with
visibilities dipping below 3SM in the heaviest rain. Also expecting
some gusty t-storm outflow for an hour or two, before winds find
their way back to a light S component.

Outside of that, have timed the best chances for showers and a few
storms at LEX/RGA later this evening, although confidence is lower
by that time, so will handle with VC mention. VFR should largely
prevail overnight.

Another round of showers and storms is expected from mid to late
morning into the early afternoon, so have tried to time that with
Prob30 mentions. More confidence will be gained in that scenario
with time.

&&

.LMK WATCHES/WARNINGS/ADVISORIES...
KY...Heat Advisory until 8 PM EDT /7 PM CDT/ this evening for
     KYZ023>034-038-045-053-061>063-070>074.
IN...Heat Advisory until 8 PM EDT /7 PM CDT/ this evening for
     INZ076>079-083-084-089>092.

&&

$$

MESOSCALE...BJS
SHORT TERM...RAS
LONG TERM...SRM
AVIATION...BJS