Area Forecast Discussion
Issued by NWS Louisville, KY

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FXUS63 KLMK 131702
AFDLMK

Area Forecast Discussion
National Weather Service Louisville KY
102 PM EDT Wed Mar 13 2024

.KEY MESSAGES...

* Unseasonably warm temps Today and Thursday.

* Periodic rounds of rain and storms Thursday into Friday. There is
  a low-end/Marginal risk for severe storms Thursday afternoon
  through Friday morning.

&&

.UPDATE...
Issued at 940 AM EDT Wed Mar 13 2024

Main forecast update this morning was to reduce overall coverage and
chances for PoPs across southern KY. Recent radar/satellite imagery
and trends as well as model data suggest very little, if any, shower
activity will drift in to our southwest CWA late this morning into
the early afternoon. Subsidence in the wake of this system passing
by should keep additional shower/storm chances too low to warrant
mention in forecast at this time, with the next (low) chances for
precip coming this evening into the overnight hours.

&&

.SHORT TERM /THROUGH TONIGHT/...
Issued at 327 AM EDT Wed Mar 13 2024

Early morning satellite imagery revealed partly cloudy skies across
the region this morning.  Temperatures exhibited a ridge/valley
split across portions of south-central KY where the valleys were in
the middle 30s and the ridges were in the mid-upper 40s.  We had a
few warmer spots out there as well with readings in the lower 50s.
Our traditional radiational cooling spots were running slightly
colder than their surrounding areas with readings in the upper 30s
to the lower 40s.  Area radars were quiet at this hour and are
expected no significant weather is expected.

For today, a weak mid-level trough axis will arrive in the region
toward sunrise.  A few of the higher resolution CAM models suggests
some scattered showers and perhaps a rumble of thunder down across
southern KY, mainly from Hopkinsville over toward the Bowling Green
area.  This activity should diminish by mid-late morning as the
upper level wave pushes off to the east and we see some ridging
building into the area.  Otherwise, another mild day is expected
across the area with afternoon temperatures warming into the upper
60s and lower 70s.  Still going to watch the late afternoon period
closely as residual outflow from this morning`s convection over MO
may result in some additional convective development over far
western KY and southern IL this afternoon.  A few of the higher
resolution CAMs continue to show this with the convection moving
eastward into our far western/northwestern areas.  We`re not overly
confident in these CAM solutions as the area will be in some slight
ridging aloft.  Convective temps are around 73 degrees for this
afternoon and most spots will probably top out just under that.  For
now, will continue to advertise a slight chance of showers/storms
across our far west/northwest this afternoon.  Brief heavy rains,
perhaps some gusty winds and lightning would be the main threats.

For tonight, we`ll be in a warm advection pattern with generally
mild conditions expected.  Isolated convection may be in progress
across portions of southern IL and into southern IN this evening and
a gradual uptick in convection is likely along a northward moving
warm frontal boundary that will be in place from central IL eastward
into central IN and OH.  Will keep a slight chance of PoPs in the
forecast for our southern IN counties with our KY counties remaining
mainly dry overnight.  Lows will be in the 50-55 degrees in many
locations.  Some cooler readings in the deeper valleys will be
possible where they could reach the upper 30s/lower 40s.

&&

.LONG TERM /THURSDAY THROUGH TUESDAY/...
Issued at 327 AM EDT Wed Mar 13 2024

Synopsis...The most prominent features in the upper-level pattern
during the medium range continue to be a closed low meandering over
the Southwest US/Baja California region and an anomalous ridge
stretching from the northeast Pacific to western Canada. Meanwhile,
weak ridging and quasi-zonal flow will prevail for the central and
eastern part of the CONUS which will eventually speed up as
shortwave trough ejects from the closed low towards the Midwest
Thursday into Friday. At the surface, the lower Ohio Valley will
start off located in the broad warm sector of a relatively weak low
over the central Plains with warm front extending across the upper
Ohio Valley. This surface low will move eastward in tandem with the
ejecting shortwave trough and allowing a cold front to push through
the forecast area Thursday night into Friday morning. During the
weekend and early next week, the Rex blocking configuration over the
West will allow amplification of the pattern downstream as a series
of shortwave troughs digging from Canada help carve a longwave
trough over the eastern half of the country.

Model Confidence/Evaluation...There is medium to high confidence in
the large scale pattern evolution through the weekend as
deterministic model guidance reasonably agrees on the upper
low/anomalous ridge position and intensity. Guidance starts to
diverge early next week with large forecast uncertainty during the
middle of the week, as shown in the WPC EOF Cluster Analysis,
related to how fast the longwave trough ejects to the east and how
models break the blocking pattern in the West. On the mesoscale,
there is low confidence in the exact storm coverage, intensity, and
timing during Thursday and Friday; however, high resolution models
have started to hint at two potential windows of severe weather
concerns: Thursday afternoon and late Thursday night into Friday
morning. On this regard, the CSU ML algorithm has kept a wind/hail
threat close enough to the forecast area while the tornado risk is
just off to the west. The aforementioned risks are supported by an
EFI between .7 to .9 through Thursday evening and slightly lower
values for Thursday night into Friday morning. One thing to note
with the CSU model is that it predicts overall probabilities in a 24-
hr window, so it is unclear which period contains the max severe
weather risk or if it follows a bimodal distribution.

Thursday...First wave of rainfall with a conditional threat of
strong to severe storms might happen Thursday afternoon. The
shortwave trough and associated surface low will be moving from the
central Plains to the Midwest during the day with ample moisture and
warm advection accompanying a 40+ knot LLJ core bisecting the Wabash
Valley with surface destabilization provided via solar radiation
during the morning and before the afternoon convection arrives. The
conditional threat of strong to marginally severe storms will be
strongly tied to the upstream convective evolution Wednesday night
as cellular storms close to the warm front/surface low intersection
grow upscale and move eastward in the warm sector amid developing SW
LLJ. Current thinking is that a broken line of storms with embedded
bowing segments could be moving across IN Thursday afternoon. That
being said, that scenario depends on several factors that are still
uncertain at the moment, which can be summarized by taking a look at
the different solutions depicted in the CAM models. Even if the
conditional threat materializes, one of the biggest questions is how
far south storms might develop. For now, will continue advertising a
conditional threat of strong to marginally severe storms for
southern IN and north-central KY Thursday afternoon with hail and w
ind threat although brief spin up tornadoes cannot be ruled out
given SRH, instability, and LCL parameters.

Thursday night - Friday...A second wave of showers and potentially
strong to severe storms will arrive late Thursday night into Friday
morning associated with the frontal passage. Storms should be
arranged along a decaying convective line since instability and
shear parameters will not be as favorable as the setup on Thursday
afternoon plus the effect of nocturnal BL stabilization and waning
frontal dynamics. On the other hand, large scale forcing could be
assisted by the right entrance region of an intensifying upper jet
and pure momentum/cold pool dynamics. Therefore, an isolated threat
of damaging winds and brief spin-up tornadoes is still on the table,
but the caveat of a low confidence forecast pending better model
agreement and uncertainties related to earlier convective evolution.

Weekend & Next Week...Temperatures will cool down to near normal
values during the weekend with dry conditions on Saturday and low
rain chances on Sunday. For next week, there is a low confidence
potential of snow showers Sunday night into Monday morning with sub-
freezing lows Monday and Tuesday night.

&&

.AVIATION /18Z TAFS THROUGH 00Z FRIDAY/...
Issued at 101 PM EDT Wed Mar 13 2024

VFR conditions expected through most of the forecast period. Latest
trends in satellite, radar, and model data are pointing toward dry
conditions for the remainder of the day. Overnight, isolated showers
and storms could impact areas across southern Indiana and northern
Kentucky, though overall coverage is too low to warrant mention in
TAF. Additional showers and storms may develop tomorrow, but
confidence in their timing and placement remains too low to warrant
mention at this time. Any site that is impacted by a heavier shower
or storm would see briefly reduced cigs/vis.

&&

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

&&

$$

UPDATE...DM
SHORT TERM...MJ
LONG TERM...ALL
AVIATION...DM


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