811
FXUS63 KLMK 171856
AFDLMK

Area Forecast Discussion
National Weather Service Louisville KY
256 PM EDT Mon Jun 17 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 Tuesday,
    then dry Wednesday through Saturday, with flash drought
    development possible.

&&

.SHORT TERM /THROUGH TUESDAY/...
Issued at 256 PM EDT Mon Jun 17 2024

A hot, humid afternoon is in progress with temperatures currently in
the upper 80s to lower 90s. Heat indices are near 100 in some areas
and will top out in the 95-105 range this afternoon. Anomalous mid
and upper level ridging will remain anchored over the Mid-Atlantic
while strengthening and expanding through Tuesday. This afternoon,
an upper level shortwave impulse is noted lifting north over the Mid-
MS Valley where convection is ongoing. Showers and some storms are
expected to continue lifting NNE through western TN/KY toward far SW
IN into this evening, bringing a better chance for rain to our far
western counties in west-central KY and SW IN. Otherwise, convection
has yet to develop in central KY and southern IN and will remain
very sparse through the evening hours. An isolated storm cannot be
completely ruled out, but most will stay hot and dry.

A few showers may linger past sunset into early tonight, but any
convection will weaken with sunset. Increased cloud cover will be
present overnight with partly to mostly cloudy skies. Expect a warm
night with Tuesday morning lows in the low to mid 70s.

Tuesday will feature a bit more cloud cover than today with
lingering mid and upper level moisture. This should help suppress
sfc heating at least a little bit. It will still be warm with
temperatures rising into the lower 90s in most areas. Afternoon heat
index values are expected to top out in the 95-100 range. Mainly dry
conditions look likely. There is a brief window during peak heating
when rain chances max out around 10-20%, but confidence is low on
shower development due to increased subsidence aloft.

&&

.LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/...
Issued at 256 PM EDT Mon Jun 17 2024

Tuesday Night - Saturday Night...

An anomalous upper ridge continues to center around the mid Atlantic
Coast region through late week, and then will try to hold onto a
flatter W-E orientation into at least the first part of the weekend.
As a result, mostly dry and hot conditions are expected to persist
under this regime. Overall, humidity values aren`t expected to be as
bad as they could be, as dew points are generally expected to range
in the mid/upper 60s most of the time. Those dew points combined
with highs in the mid/upper 90s each day Thursday-Saturday (possibly
Sunday too), are expected to yield heat indices mostly in the mid to
upper 90s each day late week into the first part of the weekend at
least. Given that overnight lows will remain quite mild, we could
get into a situation where we see a prolonged period of sub Heat
Advisory criteria, but enough of a duration where a headline could
be needed. Some initial collaborations have gone on today, but will
hold off on taking messaging farther given that heat indices really
aren`t projected to even get above 100, and that a the duration is
in question given a late weekend cool front possibly arriving. For
context, LREF probabilities of heat indices 100F or more only peak
at around 20% for the Friday/Saturday time frame.

As far as precipitation chances go, we should be mainly dry,
although some data suggests a few very isolated precipitation
chances during peak heating. A look at forecast soundings shows a
mostly capped thermodynamic profile, and given the lack of a trigger
under upper ridge, prefer to lean toward the majority of the dry
data through this stretch.

Sunday - Monday...

Lower confidence for the late weekend/early week timeframe as some
data supports the upper ridge breaking down in response to a
northern Plains shortwave tracking into the Great Lakes region. It
is possible that these lower H5 heights, and a surface cool front
trailing from the parent low pressure hold off until Monday, but
will have to wait until those details become clearer. The potential
for any long duration heat headlines could ultimately depend on what
happens Sunday, so until this becomes clearer a late week headline
is too low of a probability.

With respect to the cold frontal arrival either Sunday or Monday,
this will also bring the first shower and storm chances back to the
region since early week. Carrying chance pops in the time frame to
account, but it is possible that the hot and mostly dry conditions
ahead end up contributing to a slower frontal arrival, which will
ultimately result in a hotter/drier Sunday. Past experience has me
leaning toward the hotter/drier Sunday, but plenty of time to work
that out in coming forecasts.

&&

.AVIATION /18Z TAFS THROUGH 00Z WEDNESDAY/...
Issued at 144 PM EDT Mon Jun 17 2024

VFR conditions likely. The TAF sites appear likely to remain mainly
dry, though isolated thunderstorms are possible from mid-afternoon
through the evening hours. HNB appears to have the best chance at
seeing at least brief rain late this evening as convection moves NE
across western TN/KY into southwestern IN. Confidence in timing and
any impacts due to TSRA is low due to the limited coverage.
Thunderstorms will weaken with sunset. It does look like we`ll see
more enhanced mid-level cloud cover tonight and into Tuesday with
light southerly winds.

&&

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

&&

$$

SHORT TERM...EBW
LONG TERM...BJS
AVIATION...EBW