347
FXUS63 KLMK 030713
AFDLMK

Area Forecast Discussion
National Weather Service Louisville KY
313 AM 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. Overnight the severe
    threat will diminish but the threat of local flash flooding will
    continue with additional heavy downpours possible, especially in
    southern Indiana and north central Kentucky.

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

&&

.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 /00Z TAFS THROUGH 06Z THURSDAY/...
Issued at 1252 AM EDT Wed Jul 3 2024

The pre-dawn hours will be quiet with mostly clear skies and a light
breeze out of the south. A low level jet is expected to develop from
BNA to CMH but should remain weak enough to stay below LLWS
threshold.

Today will be a hot and muggy day as a cold front approaches from
the northwest. Scattered summertime thunderstorms are expected to
develop by late afternoon and continue into tonight. Very heavy
downpours and gusty winds will be possible with the storms.
Confidence is low in the exact location of convection, but high
enough to include PRO30s at all sites, and went ahead with a VCTS at
SDF late tonight as the front approaches the Ohio River. Winds may
be somewhat chaotic tonight with thunderstorms and various outflow
boundaries.

&&

.LMK WATCHES/WARNINGS/ADVISORIES...
KY...Heat Advisory from 1 PM EDT /noon CDT/ this afternoon to 8 PM
     EDT /7 PM CDT/ this evening for KYZ023>034-038-045-053-
     061>063-070>074.
IN...Heat Advisory from 1 PM EDT /noon CDT/ this afternoon to 8 PM
     EDT /7 PM CDT/ this evening for INZ076>079-083-084-
     089>092.

&&

$$

SHORT TERM...13
LONG TERM...EBW
AVIATION...13