825
FXUS63 KLMK 031736
AFDLMK

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

.KEY MESSAGES...

*   A heat advisory is in effect this afternoon and early evening
    for areas west of a line from Frankfort to Campbellsville to
    Tompkinsville. Heat indices within the advisory area could be as
    high as 109 degrees.

*   Scattered thunderstorms are expected to develop by mid to
    late afternoon and continue into tonight, with the greatest
    coverage over southern Indiana and north central Kentucky.
    Some of the storms this afternoon and evening will be
    capable of strong gusty winds and torrential downpours.
    Additional heavy downpours overnight could result in
    localized flash flooding, especially in southern Indiana
    and north central Kentucky.

*   Unsettled weather will continue through Friday. Strong
    storms will be possible each day with the potential for
    isolated damaging wind gusts, torrential rainfall, and
    intense lightning.

&&

.UPDATE...
Issued at 133 PM EDT Wed Jul 3 2024

Very warm and muggy air mass in place across the Ohio Valley, but
extensive cirrus blowoff from earlier MCS activity is holding temps
back slightly. Still plenty of time to realize forecast highs in the
lower to mid 90s this afternoon, with plenty of humidity to drive
heat indices into triple digits.

Hi-res models are still focused on southern Indiana for late
afternoon convection, which could expand into north central Kentucky
this evening. Look for strong to marginally severe pulse storms,
with very high PWATs supporting locally torrential downpours and
gusty winds as updrafts collapse. Minimal changes to the going
forecast.

&&

.SHORT TERM /THROUGH TONIGHT/...
Issued at 313 AM EDT Wed Jul 3 2024

Overview:
South southwest winds between high pressure over the East Coast and
a cold front stretching from the Great Lakes to Southern Plains plus
a healthy upper ridge over the Southeast will provide us with a hot
and humid day today. Scattered afternoon storms are expected to
develop in the warm, humid, unstable atmosphere this
afternoon/evening and continue into tonight as the cold front
approaches the Ohio River.

Heat:
Though there is some concern that widespread cumulus
development, scattered showers/storms, and convective debris clouds
from upstream convection may hamper insolation, it will still be a
hot and muggy day. With 850 temps nudging up a degree or two, good
warm advective flow, and a persistent air mass in place, will go a
few degrees warmer than yesterday resulting in highs in the lower
and middle 90s. Dew points in the 70s are already in place over much
of the area, and will become more widespread today as two corridors
of moisture -- one from the central Gulf Coast to the Ohio Valley
and another over the Mississippi Valley -- combine. This combination
of heat and humidity will lead to heat index readings over 100
degrees west of I-75 and into the 105-108 degree range along and
west of I-65. A Heat Advisory is already in place and will remain.
Added a few counties in the northeast after chatting with ILN.

Severe:
Scattered storms are expected to develop mid-late afternoon,
especially in southern Indiana and north central Kentucky, as the
atmosphere destabilizes, convective temperatures are met, the cold
front approaches from the northwest, and there may be outflow
boundaries and/or differential heating boundaries present. With weak
mid-level lapse rates, weak deep layer shear on the order of 20-
25kt, high freezing heights, and fairly straight hodographs, the
main severe threat today will be strong gusty winds associated with
the heaviest downpours. Sounding progs suggest convection may become
elevated after midnight tonight.

Flash flood:
With dew points in the low to mid 70s and precipitable
water amounts around 2.1 to 2.3 inches there will be plenty of
available moisture for torrential downpours. Soundings continue to
show tall, thin CAPE and some slight veering of low/mid-level winds,
further supporting the idea of locally intense rain. 850-300mb flow
is parallel with the surface boundary and lines up with the height
gradient on the periphery of the upper ridge to our south,
indicating the possibility of training storms with forward motion
around 15-25 mph and possible regeneration on outflow boundary
interactions. Looking at model 24-hour QPF, the highest amounts are
in a band coincident with the above features from Missouri through
southern Illinois and southern Indiana to Ohio. WPC QPF also favors
this area though brings it into north central Kentucky as well, and
WPC has a Slight Risk for excessive rain along and several counties
either side of the Ohio River. At this time it looks like a general
1-2" of rain will be possible tonight in southern Indiana,
interestingly right where D1 Moderate Drought currently is located.
However, while the rain may be needed, heavy rain and flash flooding
are particularly dangerous at night.

Summary:
Hot and humid today with scattered thunderstorms popping up by
mid/late afternoon, continuing into tonight. The main threats will
be locally gusty winds and heavy downpours. Localized flooding will
become the greater threat than severe weather overnight.

&&

.LONG TERM /THURSDAY THROUGH TUESDAY/...
Issued at 313 AM EDT Wed Jul 3 2024

Independence Day...

A stalled, weak sfc boundary is forecast to be in the vicinity of
southern IN and northern KY on the morning of the Fourth of July.
Rich moisture will already be in place, straddling the frontal
boundary. Precipitable water of 2.0-2.3 inches is forecast for
Thursday, which is right around the daily max PW in the BNA sounding
climatology for the first week of July.

A small mid-level shortwave impulse is forecast to lift ENE from
Missouri to Indiana Thursday morning and will bring enhanced WSW
flow aloft - 40-45 kts at 500 mb and 25+ kts at 850 mb. Enhanced
lift and low-level moisture transport associated with this wave will
result in increasing rain and thunderstorm chances Thursday morning.
Detailed convective evolution remains uncertain, but some HREF
members point to a cluster evolving east across the Wabash River
Valley early Thursday with increasing precip chances in southern IN
and north-central KY as early as mid-morning. This does seem
probable given the arrival of the mid-level shortwave trough and
associated WSW LLJ. Should storms evolve east across the northern
half of the forecast area during the morning to early afternoon time
frame, a lull would then follow for the heart of the afternoon.
Isolated or scattered redevelopment would then be possible late in
the day after a period of airmass recovery. South-central KY has a
better chance to start off the day dry with increasing rain/storm
chances by early to mid-afternoon.

While detailed timing remains problematic, showers and thunderstorms
are likely on the Fourth of July. It just won`t be an all-day rain.
Cloud cover will help limit sfc heating and destabilization. Fcst
soundings show a very moist profile characterized by tall, skinny
CAPE. Deep-layer shear could be as high as 30-35 kts, but the main
hazards will be heavy rainfall and localized flash flooding. Any
training of storms will significantly boost the local flash flood
risk. The anomalously moist environment will be supportive of
extreme rainfall rates of 2+ in/hr over relatively short time
periods. Gusty winds and intense lightning will also be possible
with thunderstorms. Cannot rule out very isolated damaging winds, as
any stronger updraft would pose an increased wet microburst threat.

Outside of scattered storms, expect a warm and humid day with
afternoon highs ranging from the mid/upper 80s north of I-64 to the
lower 90s in south-central KY.


Thursday night - Friday night...

Additional scattered showers/storms are possible Thursday night,
though a chunk of the overnight hours may stay dry. Rain chances do
increase heading into Friday as a stronger wave of low pressure
swings over the Upper Midwest and Great Lakes. This low pressure
system will drag a stronger cold front through the region late
Friday, and additional showers and storms are likely along and ahead
of the cold front. Depending on convective evolution on Wednesday
and Thursday, think the main hazard on Friday will be flooding.
There is at least a Marginal/low-end risk for isolated severe wind
gusts with the presence of stronger forcing and modest deep-layer
shear. Strong destabilization looks unlikely with clouds and precip
limiting high temps to the mid/upper 80s.

We`ll dry out Friday night with temperatures falling into the 60s in
the wake of the cold front.


This Weekend and Early Next Week...

The weekend looks dry with a much drier airmass behind the front and
weak sfc high pressure building across the region. Look for a mostly
sunny Saturday with highs in the low to mid 80s. Dewpoints are
forecast to be in the mid 60s, which will actually feel decent after
the Wed-Fri stretch. Sunday will be a bit warmer with highs in the
mid/upper 80s. Deepening troughing over the central CONUS and MS
River Valley will bring rain chances back to the forecast for early
next week.

&&

.AVIATION /18Z TAFS THROUGH 00Z FRIDAY/...
Issued at 133 PM EDT Wed Jul 3 2024

Main challenge in this TAF set is timing and impacts of convection.
Very juicy and boundary-rich environment does not lend much
confidence to that. However. would expect the best opportunity for
scattered thunderstorms this evening would impact HNB after roughly
22Z and SDF after 00-01Z. Differential heating could also get BWG in
on the act, but not confident enough to mention storms in the TAF
there.

Overnight we`ll see light S-SW winds and mostly mid-level debris
clouds. Could see a weakening MCS come in Thu morning, with MVFR
cig/vis possible. Will include this in the TAFs but confidence is
medium at best.  Winds will be light from nearly due west.

&&

.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.

&&

$$

UPDATE...RAS
SHORT TERM...13
LONG TERM...EBW
AVIATION...RAS