-- Discussion containing changed information from previous version are highlighted. --
869
FXUS63 KLMK 170107
AFDLMK

Area Forecast Discussion
National Weather Service Louisville KY
907 PM EDT Sun Jun 16 2024

.KEY MESSAGES...

*   Persistent early season heat wave expected, with highs well into
    the 90s each day.

*   Heat index values not expected to reach advisory levels, but
    societal impacts are likely.

*   Spotty coverage of afternoon thunderstorms today and Monday,
    then largely dry from Tuesday into next weekend.

&&

.UPDATE...
-- Changed Discussion --
Issued at 906 PM EDT Sun Jun 16 2024

Moisture has returned into the region via southerly flow. During the
afternoon and into this evening, dew points have steadily increased
into the low 70s and PWATs in the 1.8-2.0 inch range. An outflow
boundary from cells over Nashville tracked through southern
Kentucky, bringing forcing to increased moisture and instability. A
few cells formed along this line bringing up to half inch hail and
wind gusts up to 30mph along the gust front. These cells are
beginning to dissipate as the gust front continues to track
northwest and dusk settles in.

Convective debris clouds will linger over the region through the
first half of the overnight period. This additional cloud coverage
will slow radiational cooling. Due to this, have opted to raise
Monday morning low temperatures by about a degree. Otherwise, the
forecast remains on track.
-- End Changed Discussion --

&&

.SHORT TERM /THROUGH MONDAY/...
Issued at 320 PM EDT Sun Jun 16 2024

A strong upper level high is centered over the Carolinas this
afternoon and will remain anchored there through Monday. This upper
ridging is forecast to amplify on Monday as very subtle upper level
shortwave energy streams north over the Lower to Mid-MS Valley. At
the surface, strong high pressure is centered over Massachusetts and
is forecast to drift east over the western Atlantic through
tomorrow.

A hot and humid afternoon is underway with temperatures running in
the upper 80s to lower 90s. We still have a SW to NE low-level
moisture gradient, but sfc dewpoints have steadily risen since this
morning and are now in the mid 60s to lower 70s. Low-level SW flow
continues to advect rich low-level moisture into the region, and low
70s dewpoints are now common across western and portions of central
KY. Heat indices are expected to top out in the 95-105 range this
afternoon, with the highest values in the western and southern
portions of the CWA. While below advisory criteria, some impact to
vulnerable populations is possible. If working or spending time
outdoors, take frequent breaks in the shade or air conditioning and
drink plenty of water. Remember to check the back seat, and never
leave children or pets unattended in vehicles for any length of
time.

The hot, humid airmass has also become quite unstable, with MLCAPE
exceeding 2000 J/kg across western and south-central KY. Spotty
convection has bubbled up in Middle TN and is drifting slowly to the
northeast. Expect this convection and its associated outflow to
generate additional widely scattered convection across south-central
KY late this afternoon and evening. With steep low-level lapse rates
and high DCAPE in excess of 1000 J/kg, expect locally strong wind
gusts with any thunderstorm. Brief heavy rainfall is also likely.
This pulse convection will be relatively sparse, so most will stay
hot and dry. Convection will diminish shortly after sunset.

The more humid air flowing into the region will result in a warmer
night with lows in the lower 70s. The Louisville urban heat island
will likely only dip into the mid 70s by daybreak. Temperatures will
warm quickly once again Monday morning. Expect a hot, humid day with
afternoon highs in the low to mid 90s. Scattered afternoon
convection is expected once again, though spotty storms will be
possible area-wide. These storms will also be capable of brief heavy
rainfall and locally gusty winds (and welcome relief from the heat).

Peak heat indices near 100 degrees are forecast for Monday afternoon
and early evening.

&&

.LONG TERM /MONDAY NIGHT THROUGH SUNDAY/...
Issued at 320 PM EDT Sun Jun 16 2024

Mid and upper level ridging continues to strengthen and expand on
Tuesday with the center drifting northward slowly. There is a small
chance (10-15%) for an isolated shower or storm, but it seems
unlikely convection develops at all due to increasing subsidence
aloft. The better chance for pulse convection will be off to our
west and northwest. This will give us a hot, dry day with afternoon
highs in the low to mid 90s.

Wednesday through Friday, the strengthening East Coast ridge takes
on more of an east-west orientation, resulting in height rises and
mid-level subsidence over the Ohio Valley. This will keep a lid on
convection, and allow temps to climb into the mid/upper 90s. Still
not going too crazy with the heat index, as the warming will be
offset by dewpoints dropping into the lower 60s by Thu-Fri. It`s
nothing you`ll mistake for the desert, but just enough to take the
edge off the heat.

Small rain chances return next weekend, as the ridging starts to
show weakness across the Great Lakes. POPs still only around 20
percent but we`ll keep an eye on that for some break in the heat and
potential developing drought.

Confidence in reaching triple-digit heat indices is not high enough
for even a duration-based Heat Advisory. However, a prolonged period
of hot temperatures is very likely to cause societal impacts, so we
will ramp up messaging to core partners and be prepared to go with a
Heat Advisory if confidence in broader impacts increases.

&&

.AVIATION /00Z TAFS THROUGH 06Z WEDNESDAY/...
Issued at 724 PM EDT Sun Jun 16 2024

Isolated showers and thunderstorms have developed over southern
Kentucky. Storms will dissipate as the sun sets. The remainder of
the overnight will consist of VFR conditions. Light, southerly winds
will prevail through into the morning. By mid-morning, daytime
heating will allow for gusty winds to develop on the order of 16-
20kts. SCT Cu will develop in the afternoon, which may lead to
isolated-scattered showers and thunderstorms in the evening.

&&

.LMK WATCHES/WARNINGS/ADVISORIES...
KY...Air Quality Alert until midnight EDT tonight for KYZ029>031.
IN...Air Quality Alert until midnight EDT /11 PM CDT/ tonight for
     INZ076>079-083-084-089>092.

&&

$$

UPDATE...SRM
SHORT TERM...EBW
LONG TERM...EBW
AVIATION...SRM