587
FXUS63 KLMK 291727
AFDLMK

Area Forecast Discussion
National Weather Service Louisville KY
127 PM EDT Sat Jun 29 2024

...Updated Aviation Discussion...

.KEY MESSAGES...

*   Very warm and muggy this afternoon with heat index readings
    peaking around 100 to 105.

*   Scattered storms today and tonight, especially this afternoon
    and evening. Locally heavy rain and gusty winds will be the main
    threats.

*   Another period of unsettled weather returns to the region by
    late Wednesday and Thursday.

&&

.UPDATE...
Issued at 1022 AM EDT Sat Jun 29 2024

Morning observations reveal partly cloudy skies across much of
Kentucky with mostly cloudy skies across southern Indiana.
Temperatures had warmed into the lower 80s across southern Indiana
and much of north-central/east-central Kentucky with mid 80s across
the southwest and far southern sections.  Rather oppressive dewpoints
were noted with readings in the low-mid 70s making it feel like the
lower 90s already.

Current forecast remains in good shape this morning. Main concern
continues to be what effect the high level clouds spreading in from
the west/northwest will do to afternoon forecast temperatures and
our convective chances.  Current thinking is that we`ll have at
least scattered-broken high cloud cover over the region today and
that will impact some degree of insolation.  Overall highs in the
upper 80s to the lower 90s still look attainable.  Dewpoints in the
lower-mid 70s will be seen early in the afternoon which will push
heat index readings into the 100-105 range, before some PBL mixing
takes place and reduces the near surface moisture.

As for convection, the latest CAMs continue to show rather isolated-
scattered coverage for the afternoon.  Model soundings show rather
marginal shear profiles of 25-30kts with high wet-bulb zero heights.
Degree of instability will be determined by how warm temps get, but
it appears that we`ll have decent instability develop with MLCAPE
values jumping into the 2500-3500 J/kg range during the afternoon.
PWAT values will remain in the 2.1-2.2 inch range and storm motions
still look to be in the 15-25 mph range.  The 3km NAM solutions still
show a bit of capping up around 850 mb this afternoon.  The lack of
convection in the CAMs may be do to the lack of strong synoptic
scale forcing being absent from the region.  However, it still
appears that at least scattered storms should fire during the
afternoon mainly in an axis from roughly Bowling Green northeast
toward Lexington.  Based on soundings/environment, thunderstorms
with torrential rainfall, gusty winds, and intense CG lightning
would be the main weather hazards.  Some localized flooding could
occur, especially where storms train over the same locations.

After loading up the latest temperature/dewpoint data, still am not
seeing the need for a Heat Advisory across our region. Will continue
to monitor obs through lunchtime and decide to keep the SPS ongoing
or upgrade our far SW to a short-fused Heat Advisory.

&&

.SHORT TERM /THROUGH TONIGHT/...
Issued at 315 AM EDT Sat Jun 29 2024

Impressive MCC over Missouri overnight is pushing generally
eastward. At the time of this writing cloud tops are starting to
warm slightly, but an MCV has developed in regional radar imagery.
Given the MCV`s current track and speed as it moves through a
favorable environment of high moisture and weak shear, it would
potentially graze the southwest corner of the LMK CWA (Logan County)
around mid-late morning CDT, though its forward motion may slow some
as it drifts south of stronger westerlies over the upper Mississippi
Valley and Great Lakes. This along with a shortwave trough riding
along the periphery of a large upper ridge over the southern half of
the United States, a cold front approaching from the northwest, and
diurnal destabilization, supports the idea of scattered showers and
storms today, especially this afternoon and evening.

Synoptic scale deep layer shear will be on the order of 25-30kt
today with weak mid-level lapse rates. Degree of destabilization
will be partially dependent on how much cloudiness/insolation we
receive today, and it does appear like widespread high clouds will
limit destabilization. Wet bulb zero heights will be very high and
the column quite wet, so severe hail making it to the ground is
unlikely. With weak low level shear, that leaves gusty winds as the
main severe threat. Sub-cloud air on sounding progs is not
particularly dry and surface dew points will be in the middle 70s,
so the best shot at surface gusts will be with the heaviest
downpours as they impact the ground. SPC`s MRGL risk looks
appropriate.

Indeed, heavy downpours will be a possibility given efficient rain
producers in an atmosphere of 2.1-2.2" precipitable water values.
Forward motion of the storms should be on the order of 15-25 mph, so
some locally significant amounts of rain will be possible in any
stronger storms that develop. WPC has a MRGL risk of excessive
rainfall across the region today, which is appropriate given the
expected widely scattered coverage.

Temperatures today are tricky, given the possibility of widespread
clouds, even if only high clouds. Kept the idea of previous shifts
and ModelCertainty of going slightly below NBM for MaxT. Dew points
in the mid 70s will make for a very humid and uncomfortable day with
heat index readings peaking in the 100-105 degree range this
afternoon. After chatting with PAH, will hold off on an advisory for
now, and will keep an eye on the behavior of the widespread upstream
clouds advancing toward the area from the Midwest. Those clouds, and
the possibility of scattered showers & storms, cast doubt on whether
advisory level heat/impact will be achieved. If those clouds show
signs of dissipating and/or precipitation chances decrease, may need
to upgrade to advisory, especially west of I-65 and south of the
Ohio River.

Tonight the front will move into the Ohio Valley with scattered
showers and thunderstorms. It will be another warm and muggy night
with lows in the lower and middle 70s.

&&

.LONG TERM /SUNDAY THROUGH FRIDAY/...
Issued at 315 AM EDT Sat Jun 29 2024

===== Sunday - Sunday Night =====

The cold front will be bisecting the forecast area at the beginning
of the long term forecast period on Sunday morning, but will be
progressing to the southeast. Our counties south and east of the
Kentucky Parkways will still be in a pre-frontal airmass, supportive
of some shower activity through the morning and early afternoon.
Eventually the front will pass through the entire forecast area,
leaving behind a drier airmass in a post-frontal regime. Drier wx
will be expanding southeastward through the region by Sunday
afternoon. Cloud cover will also depart with the front, resulting in
mostly sunny skycover for most by the afternoon. The cooler NW flow
filtering in behind the front will help keep temps near normal as we
close out June, with afternoon highs in the mid- and upper-80s.

By Sunday night, an upper level ridge will be building across the
US, with a sfc high pressure centered over the Great Lakes. This
will help keep mostly clear skycover. CAA pattern from northerly flow
will allow temps to cool some 10 degrees below normals, with
readings possibly in the 50s outside of urban areas.


===== Monday - Tuesday =====

Broad sfc high pressure centered to our north will continue to
dominate our forecast for the first two days of July. Dry weather is
expected both days. Fairly strong CAA will keep temperatures below
normal for Monday. Afternoon highs will only reach the low 80s,
which would be nearly 8-10 degrees below normals too. With dewpoints
in the 50s, Monday should be a very nice day.

On Tuesday, the sfc high will shift over to the New England region,
which will drastically change our air advection regime. With the
high to our northeast by then, the Ohio Valley will switch over to a
WAA pattern in the return flow zone. This will result in temps
returning to the 90s, and slightly above climo normals.


===== Wednesday - Friday =====

An upper shortwave will flatten out the ridge by Tuesday night and
into Wednesday, resulting in a change in the pattern for the mid-
and late-week and Fourth of July holiday. Beginning on Wednesday, we
will start off dry, but PoPs will be increasing through the late
morning and afternoon hours as a cold front approaches the Ohio
Valley. Ahead of the front, plenty of theta-e advection will ramp up
our moisture content again, likely pushing dewpoints into the mid-
70s. Accompanied with temps reaching the mid-90s, we`ll likely have
heat indices over 100 degF. Wednesday certainly does not appear to
be a wash out, but a few scattered showers and storms in the
afternoon appear possible.

Greater chances for showers and storms will be on Thursday (July 4)
as the front gets hung up across Indiana and we get reinforcing
support from another mid-level wave and vort max. Currently do not
expect the front to meander south of the Ohio River, but moisture
convergence along the front will enhance our chances for showers and
storms throughout the entire day. PoPs will also linger into Friday
as moisture transport remains high. Daily highs in the low 90s will
accompany muggy dewpoints, resulting in heat indices near 100 for
both Thursday and Friday as well.

&&

.AVIATION /18Z TAFS THROUGH 00Z MONDAY/...
Issued at 127 PM EDT Sat Jun 29 2024

VFR conditions are expected through much of the TAF period.  Could
still see some scattered showers/storms this afternoon/evening ahead
of an approaching cold front.  Best chances may be over at KHNB and
KLEX during the period.  Frontal boundary will drop southward
overnight and pass though KHNB by 30/08Z and then through KSDF
around 30/09Z, KLEX around 30/13Z and then BWG a little later.

&&

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

&&

$$

UPDATE.......MJ
SHORT TERM...13
LONG TERM....CJP
AVIATION.....MJ