343
FXUS63 KLMK 180721
AFDLMK

Area Forecast Discussion
National Weather Service Louisville KY
321 AM EDT Tue Jun 18 2024

.KEY MESSAGES...

*   Persistent early season heat wave expected, with highs well into
    the 90s each day this week, and heat index values approaching
    100.

*   Spotty coverage of afternoon thunderstorms today, then dry
    Wednesday through Saturday.

*   Flash drought development possible next week.

&&

.SHORT TERM /THROUGH TONIGHT/...
Issued at 321 AM EDT Tue Jun 18 2024

Hot weather continues today, with the main question mark being the
extent and coverage of afternoon convection. Upper-level ridge
centered along the VA/NC border will expand westward through the
day, but deep southerly flow will have the Ring Of Fire pattern as
close as western Kentucky. Low-level thickness progs suggest temps
this afternoon will fall a couple degrees short of Monday, and
dewpoints near 70 will support heat index values in the mid/upper
90s, perhaps touching 100 in the urban areas.

While the ridging will reduce cloud cover in areas from Lake
Cumberland up through the Bluegrass, there could still be a window
for isolated storms around peak heating. Farther north and west,
precip chances could run more toward 30 percent, and with a juicy
and weakly sheared environment a few pulse storms could produce
locally gusty winds.

Convection will wind down quickly with the loss of heating, so any
POPs after sunset will be restricted to southern Indiana.

&&

.LONG TERM /WEDNESDAY THROUGH MONDAY/...
Issued at 321 AM EDT Tue Jun 18 2024

Synopsis...Highly anomalous mid-level blocking high, positioned over
the Eastern Seaboard at the beginning of the period, will eventually
move southward and extend latitudinally over the southern half of
the CONUS in response to increased activity of upstream troughing
moving over the Upper Midwest/Great Lakes and tropical upper cold
low punching across the Gulf of Mexico. Therefore, additional hot
and humid days with heat indexes in the mid to upper 90s are
anticipated through the weekend with rain chances and potentially
some heat relief possible on Sunday accompanying a front.

Model Confidence/Evaluation...There is high confidence in the
temperature/heat index forecast through Saturday given agreement
among models in the evolution of the mid-level blocking high.
Besides the uncomfortably hot and humid conditions, there is a non-
zero chance of a few record highs late this week supported by EFI
maximum temperature and NAEFS/ECWMF ESAT mid-level height values. On
the other hand, confidence in Wednesday PoP lowers with respect to
the rest of the week based on the still close position of the
moisture plume axis advecting from the Gulf of Mexico to the
Mississippi Valley. Next window for showers and storms will arrive
on Sunday ahead of a weak front approaching from the west. However,
uncertainties remain regarding moisture availability after the hot
and dry spell plus model differences in spatial coverage. That being
said, severe weather probabilities are negligible given warm
temperatures aloft and weak deep layer shear.

Wednesday - Saturday...Expect temperatures to keep rising, at least
a few more degrees, as the center of the anomalous mid-level high
transitions over the Lower Ohio Valley during the Thursday-Saturday
timeframe. Best chances to tie or break afternoon highs would be
Saturday at SDF (98) and LEX (97). As mentioned in the previous
discussion, a heat advisory could still be considered due to
combination of afternoon heat indexes in the upper 90s and mild
overnight lows for an extended period of time. Regarding
precipitation potential, mostly dry conditions will persist the rest
of this week and the first half of the weekend, but a few isolated
showers and a stray thunderstorm cannot be ruled out Wednesday as
the high remains to the east and southerly winds favor weak moisture
convergence over the forecast area.

Sunday - Tuesday...Have continued indicating increasing rain and
storm chances ahead of the incoming front; however, spatial coverage
and convective intensity is still uncertain based on mesoscale
factors difficult to forecast at this time and synoptic differences
found in the guidance. Even with the arrival of wetter conditions,
forecast indicates highs in the lower 90s at the start of next week.
Additional upstream shortwave energy and the potential interaction
with tropical moisture from a Gulf surface low (as suggested by some
runs of the GFS and ECMWF) could yield additional rain/storm chances
the rest of next week.

&&

.AVIATION /00Z TAFS THROUGH 06Z WEDNESDAY/...
Issued at 1247 AM EDT Tue Jun 18 2024

Evening convection has pretty much dissipated, leaving us with a
muggy night with light winds from the south and mainly cirrus
debris. Expect VFR through the valid TAF period, with winds picking
up out of the SSW to just shy of 10 kt with mixing later in the
morning. Look for few-sct diurnal cu at 4-5K feet with a cirrus
ceiling above, but building heights aloft should keep a better lid
on convection in the afternoon. Winds will decouple around sunset
with light SE flow expected after dark.

&&

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

&&

$$

SHORT TERM...RAS
LONG TERM...ALL
AVIATION...RAS