998
FXUS63 KLMK 022335
AFDLMK

Area Forecast Discussion
National Weather Service Louisville KY
735 PM EDT Tue Jul 2 2024

.KEY MESSAGES...

*   A heat advisory is in effect Wednesday afternoon and evening for
    areas primarily along and west of the I-65 corridor. Heat
    indices within the advisory area could be as high as 107
    degrees.

*   Unsettled weather expected Wednesday afternoon through Friday
    with daily chances of showers/storms.  Strong storms will be
    possible each day with potential for isolated flash flooding.
    Isolated damaging wind gusts, torrential rainfall, and intense
    lightning will be the primary hazards.

&&

.SHORT TERM /THROUGH WEDNESDAY/...
Issued at 340 PM EDT Tue Jul 2 2024

Summertime temps and humidity are slowly making a return to the
region today. Southerly return flow on the back side of a ~1025mb
high centered near the Mid-Atlantic has helped to push temps well
into the 80s and even some low 90s at this hour, with dewpoints
climbing into the low 70s (southern KY) to ~60 (southern Indiana).
Despite a cu-field developing where dewpoints are higher, warmer air
aloft has helped to suppress any sort of vertical convective
development so storm chances should be near 0% for the remainder of
the day.

Except for some passing high clouds, skies will clear out overnight.
The region will be on the outer fringes of a LLJ that will develop
and stretch from the central Plains into the upper Ohio Valley,
which will help to keep surface winds steady but generally light
(<10kts). This will also result in overnight lows not falling to
more typical climo values, and it`s possible some urban areas could
stay in the 80s for the majority of the overnight period.

The forecast for tomorrow is a bit complicated and will be heavily
influenced by how convection evolves over the Midwest. Some high-res
models indicate that a decaying line of showers/storms may push into
the region tomorrow morning, leaving an outflow boundary lingering
across portions of southern Indiana and/or central Kentucky for
additional development later in the day. Additionally, a weak
frontal boundary across southern IL into central IN will likely
serve as a focus for more convective development tomorrow afternoon,
and those showers/storms will likely drift into the region by late
afternoon or early evening.

These showers and storms will be moving into an environment with
marginal deep layer shear (20-30kts effective bulk shear) but modest
instability and DCAPE to support wet microbursts in the stronger
convection. Therefore, the greatest severe risk tomorrow will be
damaging winds in the strongest storms. On top of the wind threat,
PWATs will be quite high (>2") so torrential rainfall is likely in
many of the showers/storms. The orientation of storm motions to the
projected outflow/frontal boundaries do raise some concern, as they
are nearly parallel which would result in localized training of
storms that may drop several inches of rain in a short amount of
time. Where these boundaries set up still remain a bit uncertain,
and the scope of the threat doesn`t look large enough to support a
flood watch, but localized flash flooding does look possible in this
setup.

Another concern going into tomorrow is heat potential. While the
convective evolution and any potential clouds from leftover morning
storms may limit or slow down heating during the day tomorrow, there
is enough confidence to go with a heat advisory for portions of the
CWA (mainly along and west of I-65) tomorrow afternoon. Confidence
is lowest across the north where convection would have the greatest
impact on temperatures.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH TUESDAY/...
Issued at 340 PM EDT Tue Jul 2 2024

Looking into the long-term, beginning Wednesday night, an upper high
will cover the southeastern US while a shallow upper trough,
centered over the Rockies, directs west-southwest flow from the
Central Plains towards New England. This places southern Indiana and
central Kentucky in the area in-between the main flow and the high
to the south. This also lines up with where a southwest to northeast
or west to east oriented front will be located, and with surface
high pressure sitting just off the Atlantic Coast, lots of Atlantic
and Gulf moisture will be funneled up the Mississippi and Ohio River
Valleys, into the CWA and along the front. This front will sit near
or over the CWA until the upper trough begins to amplify and
generates a cold front that pushes east across the Lower Ohio Valley
Friday afternoon.

Timing is still impossible to lockdown, but don`t think the period
will be a total washout. Currently, it looks like Wednesday night
into Thursday morning could be more active with a break sometime on
Thursday before the heating of the warm air mass causes more
convection to develop during the afternoon and evening hours. Expect
isolated to scattered storms for period before the passage of the
cold front on Friday, but it`s not going to non-stop rain. It`s
summer time convection. There will be winners and losers.

Precipitable water values could increase up to around 3" along this
front, according to the NAM. Most of the ensembles have this values
around 2.25" spread out over a larger area, and some of the global
models are sitting a little higher than the ensembles. Generally,
north of the front to near Indianapolis values tend to be higher
than south of the front. PWATs over 2" could cover Indiana up to
around Indianapolis while south of the front, PWATs drop off
quicker, but not by much. PWATs could still be around 1.8" or so
near Clinton County, and when PWATs are over 2" around here, it
doesn`t take much to be concerned with intense rainfall. 3" PWATs
are unheard of, so if this materializes and depending on where the
front sets up, we could see some areas of flash flooding or at least
ponding of water.

The severe threat appears to be limited. During Thursday and Friday,
models soundings show deep saturation with lots of "long skinny
CAPE", and with temperatures in the upper 80s to 90 for highs,
believe heavy rainfall will be the main concern. MLCAPE values are
slightly over 1,000 J/kg. Some gusty winds with isolated to scattered
storms will be possible, but with the likelihood of precipitation
riding along the front from west to east, the risk of training
convection concerns me more than the wind threat.

In general believe this system has trended farther south towards the
Interstate 64 corridor. Yesterday, it appeared more of the activity
would be slight farther to the north over south-central Indiana.

Behind the front, high pressure will bring mostly clear skies with
lower dew points in the mid 60s. With temperatures in the mid 80s to
near 90, this will feel slightly better.

&&

.AVIATION /00Z TAFS THROUGH 06Z THURSDAY/...
Issued at 734 PM EDT Tue Jul 2 2024

VFR conditions expected through this forecast cycle outside of some
shower and storm chances arriving for the northern TAF sites of
HNB/SDF by late tomorrow afternoon and early evening. Locally heavy
rain and gusty winds would be possible with any storm during that
time, and have included in the Prob30 mention.

Outside of that, generally quiet weather is expected through tonight
and the first part of tomorrow. Look for a few-sct cumulus layer
tomorrow with some SW gusts up around 20 knots possible through the
afternoon.

&&

.LMK WATCHES/WARNINGS/ADVISORIES...
KY...Heat Advisory from 1 PM EDT /noon CDT/ to 8 PM EDT /7 PM CDT/
     Wednesday for KYZ023>031-034-038-045-053-061>063-070>074.
IN...Heat Advisory from 1 PM EDT /noon CDT/ to 8 PM EDT /7 PM CDT/
     Wednesday for INZ076>078-083-084-089>092.

&&

$$

SHORT TERM...DM
LONG TERM...KDW
AVIATION...BJS