775
FXUS63 KLMK 231733
AFDLMK

Area Forecast Discussion
National Weather Service Louisville KY
133 PM EDT Sun Jun 23 2024

...Updated Aviation Discussion...

.KEY MESSAGES...

*   Scattered showers and storms likely today, some of which could
    be strong to severe. Damaging wind gusts and torrential rainfall
    would be the most likely threats in the strongest storms.

*   Heat Index may rise above 100 degrees on Tuesday, especially
    west of the I-65 corridor.

*   Another round of scattered showers and storms possible Wednesday
    ahead of a frontal boundary.

&&

.UPDATE...
Issued at 1036 AM EDT Sun Jun 23 2024

At mid-morning a cold front reached from low pressure east of
Georgian Bay through northern Indiana and eastern Illinois to
southern Missouri. Impressive moisture pooling along/ahead of this
boundary has led to precipitable water values of 2-2.2" and surface
dew points in the middle 70s.

Overall destabilization has been hampered by widespread clouds and
areas of rain this morning, and instability remains the biggest
question mark for this afternoon. Mid/upper dynamic support will
actually be weaker this afternoon than this morning as stronger
winds aloft weaken and push off to the east; and mid-level lapse
rates remain weak. Still, with frontal forcing and some 850mb theta-
e ridging, along with potential differential heating boundaries from
morning clouds plus the aforementioned rich moisture supply, spotty
storm development is still in the forecast for this afternoon,
primarily in central Kentucky (some minor redevelopment has already
occurred in south central Indiana this morning despite clouds and
lack of instability). Additional afternoon storm development can be
expected on outflow boundaries from collapsing cells, as well. While
sub-cloud dew point depressions aren`t expected to be particularly
large today, a column of 1000-1300J/kg DCAPE is already in place
ahead of the front and this will translate through the Ohio Valley
this afternoon as the front pushes in. As a result, locally gusty
winds associated with the heaviest downpours will be the main
threat, especially east of I-65. Some small hail in the tallest
storms can`t be ruled out, given WBZ heights around 9-10k`, but the
fairly weak shear and wet column should prevent large hailstones
from forming and making it to the surface.

Torrential downpours will be possible with any cells that develop
this afternoon. While widespread flooding is not expected due to the
scattered nature of the convection, storm motion around 20-25 mph,
and a lack of training, folks out on the road should be on the
lookout for these heavy rainers and be sure to reduce speed and turn
on headlights when in an area of very heavy rain.

At this writing temperatures are still only in the middle 70s in
southern Indiana and north central Kentucky, with widespread cloud
cover upstream. So, went ahead and knocked down MaxT a bit in those
areas.

Issued at 534 AM EDT Sun Jun 23 2024

Radar imagery from 0930z this morning shows the line of showers and
storms holding together a bit more CAMs had earlier advertised.
Analyzing the finer mesoscale details, it appears a weak/subtle
corridor of MUCAPE has advected along with the line to help sustain
or develop new updrafts. Additionally, surface temperatures are a
bit warmer than what models had depicted, with some sites still
reporting low 80s, which has resulted in a weaker capping inversion.
The weaker cap has allowed for the outflow boundary ahead of the
precipitation to initiate showers/storms more easily vs what CAMs
were depicting.

Taking all of this into account, have bumped up PoPs this morning
across our southern Indiana counties and portions of northern
Kentucky into the likely range. Still think the line will steadily
weaken and dissipate over our region, though confidence on its
eastward extent is low. Rest of forecast remains on track.

&&

.SHORT TERM /THROUGH TONIGHT/...
Issued at 231 AM EDT Sun Jun 23 2024

Currently mostly clear and quiet to start off the early morning, but
some changes are on the way as a frontal boundary slides toward the
region. 06z surface analysis shows the front stretching from Kansas
into the Great Lakes region, with a line of showers and
thunderstorms ahead of it. These showers and storms will steadily
weaken and decay as they get closer to our neck of the woods near
dawn as they out-run the frontal boundary, but may provide some much
needed (albeit light) rainfall to portions of southern Indiana and
northern Kentucky before it completely fizzles out.

The frontal boundary will eventually dive into our region this
afternoon, and should serve as a focus for scattered convective
development. Additional mesoscale boundaries from the morning
activity could also help to spark showers/storms. Most guidance
indicates that the frontal boundary will be near the Ohio River by
the time we reach convective temperatures, which will result in the
majority of our shower/storm activity staying confined to central
Kentucky for the afternoon hours.

We should clear out and destabilize enough to warrant a low-end risk
for isolated to widely scattered strong/severe storms. Biggest
limiting factor for a more impactful severe event will be the
marginal deep layer shear (<30kts 0-6km bulk shear). Main threat
with the stronger storms will be gusty winds given DCAPEs likely
exceeding 1,000 J/KG. Torrential rainfall will be likely in storms
as well given a very moist airmass (PWATs >2"), though the spotty
coverage of showers and storms today should limit any sort of flood
threat.

Drier air will move in behind the front and we should clear out
overnight. Weak surface high pressure will be nearly overhead by
dawn tomorrow so there could be patchy fog for the morning hours,
particularly where rainfall occurred.

&&

.LONG TERM /MONDAY THROUGH SATURDAY/...
Issued at 231 AM EDT Sun Jun 23 2024

Monday - Monday Night...

The long term period will begin with high pressure over the Ohio
Valley and broad ridging slowly moving east. These features will
result in clear skies, light winds, and warm temperatures. Expecting
to see temperatures in the upper 80s and low 90s on Monday. Dew
points are forecasted to be in the low-mid 60s. Monday should be a
pleasant summer day.

Tuesday - Tuesday Night...

Ridging aloft will weaken and surface high pressure will drift
southeast of the region. This will lead to southwesterly flow and
returned moisture. Dew points will rise into the upper 60s and low
70s. With temperatures forecasted in the low-mid 90s, this will
bring heat indices into the upper 90s and low 100s (west of I-65). A
weak shortwave trough will enter the region Tuesday afternoon,
bringing weak forcing to present moisture and instability. Would
expect to see some convective initiation in the later afternoon and
into the evening. Lapse rates and shear suggest unorganized
summertime convection.

Wednesday - Wednesday Night...

Troughing will deepen over the region bringing better forcing over
the region where moisture is still present. Wednesday will be the
best chance for much needed rain. PWATs will be in the 1.8-2.0 inch
range, accompanied with a well saturated column. Should be able to
get 0.25-0.75 inches of rain, with locally higher totals possible.
Wednesday evening, troughing will begin to push eastward and the
`cold` front will also push through the area.

Thursday - The Weekend...

High pressure and broad ridging will move over the Ohio Valley,
bringing dry and warm weather through the end of the week. By the
weekend, high pressure will shift east, and southwesterly flow will
bring returned moisture. Above normal temperatures are expected over
the weekend. Troughing over the northern Plains will deepen and move
eastward through the weekend, leading to increased chances for
showers and storms.

&&

.AVIATION /18Z TAFS THROUGH 00Z TUESDAY/...
Issued at 132 PM EDT Sun Jun 23 2024

A cold front poised just north of the Ohio River at issuance time
will push southward across central Kentucky this afternoon, sparking
scattered showers and storms. While prevailing conditions will be
VFR once the morning low clouds lift a bit more, TSRA will be
capable of producing well below VFR flying conditions (mostly in
terms of low vsby in heavy downpours) and enhanced wind gusts.

Storms will dissipate and move out of the region this evening as the
cold front moves off to the southeast. Clear skies and light winds
will be the rule tonight ahead of high pressure over Illinois.
Valley fog can be expected by dawn, but more widespread general fog
is more in question. Before introducing vsby restrictions in the
TAFs for early morning BR/FG, will see where rain falls this
afternoon and then re-evaluate for the 00Z package.

&&

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

&&

$$

UPDATE...13/DM
SHORT TERM...DM
LONG TERM...SRM
AVIATION...13