562
FXUS63 KLMK 170125
AFDLMK

Area Forecast Discussion
National Weather Service Louisville KY
925 PM EDT Fri Aug 16 2024

.KEY MESSAGES...

*   Strong to severe storms will be possible Saturday afternoon and
    evening. The main threats are damaging winds, hail, and heavy
    rainfall. There is a low, but non-zero tornado risk.

*   Scattered showers and storms will be possible Sunday afternoon,
    but severe weather is not expected. Lingering isolated showers
    will be possible on Monday, mainly east of US 127.

*   Dry weather is expected for much of next week, with well below
    normal temperatures.

&&

.UPDATE...
Issued at 925 PM EDT Fri Aug 16 2024

Conditions are still warm and very muggy after sunset, with KY
Mesonet obs reporting temps in the upper 70s and low 80s, along with
dewpoints in the 70s. A few very isolated showers have popped in our
area, likely where there may be some diffuse boundaries from
earlier, but also some slightly better theta-e advection and
lingering MLCAPE. Otherwise, SBCIN is beginning to spread
throughout, and should result in mostly dry conditions for the
overnight. Perhaps some patchy valley fog will be possible in some
areas by tomorrow morning, but otherwise no impacts to the region.
Updated forecast products have been published for the evening, and
everything remains in good shape. See short term section below for
more details into tomorrow.

&&

.SHORT TERM /THROUGH SATURDAY/...
Issued at 325 PM EDT Fri Aug 16 2024

Scattered convection lingers in the Lake Cumberland region this
afternoon within an axis of deep moisture (PW near 2 inches). Low-
level forcing has diminished since this morning`s wave of
convection, and most areas will stay dry this evening and overnight.
Cannot rule out an isolated shower or storm this afternoon and
evening, however. The low-level airmass continues to warm and
destabilize, and isolated development could occur along a
differential heating zone or perhaps subtle remnant outflow
boundaries from early day convection. However, coverage is expected
to remain isolated.

Tonight will likely be dry with patchy fog development. A closed low
will continue to rotate southeast over Michigan through tomorrow,
with mid/upper level troughing digging southeastward over the Ohio
Valley. This will provide increased forcing for ascent and
strengthening low to mid-level westerly flow immediately downstream
of the synoptic cold front. This increased forcing arrives
coincident with the diurnal instability maximum, which should be
more than sufficient given a lack of morning precip. Fcst soundings
show a very warm, well mixed BL with fairly steep low-level lapse
rates by early afternoon. Most hi-res CAMs suggest isolated
convective development over southern IN and central KY by 17Z, with
scattered to numerous showers/storms possible 19-00Z. Some strong to
severe storms are likely.

Sfc-based CAPE will likely peak above 2000 J/kg Saturday afternoon,
with effective bulk shear of 30-35+ kts. Low-level SRH of 100-150
m2/s2 looks likely, which could support some updraft rotation. Fcst
soundings do show rather high LCLs through much of the afternoon,
however. There is a low, but non-zero tornado risk. The main threat
is isolated damaging winds given the more favorable low-level
thermodynamic environment. Hail will also be possible in the
stronger storms, along with heavy rainfall. Some localized water
issues are possible, though the storms will be progressive. Any
localized storm mergers, or unusual training, could produce very
localized flash flooding.

Tonight will be humid with lows in the upper 60s to lower 70s. Temps
should max out in the upper 80s to lower 90s Saturday afternoon.

&&

.LONG TERM /SATURDAY NIGHT THROUGH FRIDAY/...
Issued at 325 PM EDT Fri Aug 16 2024

Saturday Night - Monday...

Tomorrow evening, scattered clusters of strong or severe
thunderstorms should be ongoing around sunset, with convective
active focused in the vicinity of a cold front which will be
dropping from NW to SE through the Ohio and Tennessee valleys.
Current short-to-medium range guidance suggests the potential for
strong to severe storms will end by around sunset across southern IN
as the effective boundary passes through, but should continue until
around or just after midnight across central and southern KY. Would
expect a trend toward upscale growth of storms into larger linear
segments later in the evening, causing damaging winds to be the
primary severe threat in addition to general thunderstorm threats of
heavy rainfall/flooding and lightning.

Sunday morning should bring a break in showers and storms as the
frontal boundary pushes into Tennessee. However, by Sunday
afternoon, diurnal heating should combine with lingering low-level
moisture to allow another round of showers and storms to develop,
with the greatest coverage expected along and east of I-65. It
should be noted that the "fuel" available for storms on Sunday
shouldn`t be nearly as plentiful as on Saturday afternoon, and the
instability profiles are less conducive for explosive convection
(i.e. "tall, skinny CAPE"). Shear should also be less on Sunday,
with W/NW low-level winds and weaker mid-level flow reducing
effective shear to between 15-20 kts. As a result, expect something
akin to "garden variety" showers and storms Sunday afternoon into
the early evening, with convection tapering relatively soon after
sunset.

Temperatures should be noticeably cooler on Sunday as low-level cold
advection moves in behind the cold front. Continued low-level CAA
via NW winds should continue into Monday, with highs remaining below
normal across the region. Another lower chance for showers or a
storm will be possible on Monday ahead of a secondary boundary which
should bring much drier air into the region for the middle of next
week. Most of the precipitation should remain east of US 127 on
Monday, and all areas should be dry by Monday evening.

The Rest of Next Week...

Behind this last wave of precipitation Monday afternoon, anomalously
dry air should move across the region for much of the rest of next
week. ECMWF ensemble mean PW remains below the 10th percentile of
model climatology from Tuesday through Thursday, with GEFS/CMC
ensembles showing a similar picture. In addition to the dry air,
temperatures are expected to remain quite modest for mid-August,
with a strong area of sfc high pressure funneling cool air from
central Canada southward through the mid-week period. Ensembles are
also supportive of below normal temperatures, with the ECMWF Extreme
Forecast Index having values below -0.8 for MaxT and MinT next
Tuesday and Wednesday. In fact, there is high confidence in lows in
the 50s and an outside potential for lows in the upper 40s in the
coldest locations next Tuesday and Wednesday morning. Temperatures
will begin to recover next Thursday and Friday as the sfc high and
upper ridge axis starts to shift eastward, with dry weather
continuing into the end of next week.

&&

.AVIATION /00Z TAFS THROUGH 06Z MONDAY/...
Issued at 727 PM EDT Fri Aug 16 2024

An isolated shower or two will remain possible across the region
this evening, but chances are low enough to not mention any precip
in the TAF. Going forward, expect VFR conditions for the period.
Clouds clear out for tonight, but will likely build back in for
tomorrow as a cold front passes through the area. Showers and storms
should begin to develop over portions of southern IN and central KY
around 17-19Z Sat ahead of a cold front. Southwesterly winds will
again increase during the daytime, possibly gusting to over 18kts.
Kept mention of TSRA in PROB30 groups for tomorrow afternoon.

&&

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

&&

$$

UPDATE...CJP
SHORT TERM...EBW
LONG TERM...CSG
AVIATION...CJP