785
FXUS63 KLMK 181621
AFDLMK

Area Forecast Discussion
National Weather Service Louisville KY
1221 PM EDT Tue Jun 18 2024

...Forecast and Aviation Update...

.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.

&&

.UPDATE...
Issued at 1221 PM EDT Tue Jun 18 2024

No changes to the going forecast as hot and humid temperatures
continue along with afternoon and evening shower and storm chances.
Like the going precipitation chance gradient from W to E, with the
most likely coverage along and west of I-65 later today. This also
lines up with the highest PWAT gradient, and fits the "ring of fire"
conceptual model on the western periphery of the upper ridge. There
won`t be a whole lot of triggering out there, however a subtle
shortwave coming out of the lower Mississippi River Valley later
today could be enough to spark additional coverage of showers and
storms. This feature may also provide a bit of an uptick in deep
layer shear, with some values in the PM reaching up around 20-25
knots. This is still pretty marginal for any real organization, but
can`t rule out a briefly more organized updraft if those values are
realized closer to 25 knots. Outside of that, this is mainly
instability driven with strong instability developing this
afternoon. Any storms farther east will have better DCAPE values to
work with given the slightly "drier" airmass, however any storms
across the west could be gusty as well with briefly heavy downpours
and some water-loaded downbursts. Can`t rule out a briefly severe
storm or two, but most activity should stay sub-severe again this
evening.

&&

.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 /12Z TAFS THROUGH 18Z WEDNESDAY/...
Issued at 1221 PM EDT Tue Jun 18 2024

Expecting mostly VFR at the TAF sites through this afternoon and
evening, with the caveat that a brief t-storm chance will exist
mainly at BWG/HNB. Like the going mention of thunder potential at
those sites, with chances farther east lesser due to low coverage
and a less favorable environment. Therefore, will keep mention out
at SDF/LEX/RGA.

Outside of the storm chances, expecting a fairly quiet period with
steady SSW winds this afternoon shifting to a lighter SE component
overnight. Cloud cover will feature diurnally driven cumulus with
some variable mid and upper cloudiness as well.

&&

.CLIMATE...
Issued at 1124 AM EDT Tue Jun 18 2024

================== Near-Record High Temps ==================

             Thursday 6/20/2024
          Max T Fcst/Record (Year)

Louisville:       96/100     (1953)

Bowling Green:    94/102     (1936)

Lexington:        95/100     (1953)



               Friday 6/21/2024
          Warm Min T Fcst/Record (Year)

Louisville:            98/98     (1988)

Bowling Green:         97/102    (1933)

Lexington:             97/97     (1988)



             Saturday 6/22/2024
          Max T Fcst/Record (Year)

Louisville:       98/100     (2022)

Bowling Green:    97/102     (1901)

Lexington:        97/99      (1988)



                   Sunday 6/23/2024
               Warm Min T/Record (Year)

Louisville:            95/98      (1988)

Bowling Green:         96/104     (1930)

Lexington:             93/96      (1988)


Note 1: Sunday temperatures are highly dependent on the arrival
of an approaching cool front. If the front ends up slower, as
some data suggests, then forecast temperatures will trend
warmer.

Note 1: Some records may have duplicate years. The latest year
the record occurred is displayed.

&&

.LMK WATCHES/WARNINGS/ADVISORIES...
KY...Air Quality Alert from midnight Wednesday night to midnight
     EDT Thursday night for KYZ029>031.
IN...Air Quality Alert from midnight EDT /11 PM CDT/ Wednesday
     night to midnight EDT /11 PM CDT/ Thursday night for
     INZ076>079-083-084-089>092.

&&

$$

UPDATE...SRM
SHORT TERM...RAS
LONG TERM...ALL
AVIATION...BJS
CLIMATE...BJS