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000
FXUS63 KLMK 180125
AFDLMK

Area Forecast Discussion
National Weather Service Louisville KY
925 PM EDT Wed Apr 17 2024

.KEY MESSAGES...

*   Strong to severe storms possible Thursday evening and overnight.

*   Much cooler weather this weekend.

&&

.UPDATE...
Issued at 920 PM EDT Wed Apr 17 2024

Cold front draped across Kentucky is most evident as a dewpoint
gradient, with dewpoint values in the lower/mid 60s to the south,
but dropping into the upper 40s behind the front. Winds are actually
slacking off fairly quickly behind the front, and with clear skies
this will allow a noticeably cooler night compared to last night.
Min temp forecast in the 50s is pretty well on track, so no changes
planned at this time.

&&

.SHORT TERM /THROUGH THURSDAY/...
Issued at 327 PM EDT Wed Apr 17 2024

Looking at satellite imagery and wind observations, the cold front,
stretching from the low pressure system over the western Great
Lakes, can be seen stretching northeast to southwest through the
CWA. As this front continues to the east this afternoon and evening,
southern Indiana and central Kentucky will see gusty winds veer
towards the west. Dry air in the 850 mb level is killing any chance
for convective weather. This is a good thing given the strong shear
in the region. This dry layer is also helping to lift and clear
skies.

Tonight, zonal flow will push a ridge of surface high pressure east
into the Lower Ohio Valley. This will cause winds to become more
variable and quickly ease as a low level inversion develops. Across
far southern Kentucky, light warm air advection along with the
possibility of some late night to early morning sky cover will lead
to low temperatures only dropping into the low 60s. Lows are
expected to taper cooler to the north with our northern communities
falling into the low 50s.

Tomorrow, as the surface high over eastern Tennessee gets pushed to
the east and a surface low, along an approaching cold front, over
Oklahoma gets pushed east, it will begin to influence the CWA. Winds
will veer from mostly the east in the morning to the south by the
afternoon. They will also increase to 10-15 mph west of Interstate
65. Gusts could reach to around 20 mph. East of 65, most areas will
see 5-10 mph winds. Skies will be mostly sunny across the CWA, but
as the surface low quickly moves from Oklahoma to Illinois during
the day, increasing clouds will begin to move into the our southern
Indiana counties from the northwest. The added sunshine and warm air
advection will help lift high temperatures into the low to mid 80s.

&&

.LONG TERM /THURSDAY NIGHT THROUGH WEDNESDAY/...
Issued at 327 PM EDT Wed Apr 17 2024

Thursday Night through Friday Night...

A period of active weather for portions of the region looks likely
for Thursday night as a weakening surface low pressure system tracks
from the Mid-MS Valley northeastward into central IN/OH with a
trailing cold front sagging southward through the lower Ohio Valley
overnight.  Convection is expected to be well developed in the form
of a linear MCS prior to the start of the forecast period.  This MCS
is likely to extend from central IN southwestward through southern
IL/eastern MO/western KY.  A well mixed boundary layer will be in
place ahead of this line promoting the potential for a large scale
wind damage event focused on eastern MO/southern IL and western KY.
The majority of the convective allowing models suggest this line
will move east southeast in the evening with the potential for the
apex of a bowing line to impact western KY and into portions of
northwest TN.  Convection will likely spread into central KY by mid-
late evening and into the overnight, but the severity of the
convection will likely be determined by how quickly the line can get
here and take advantage of the available instability.  Instability
will wane after sunset with nocturnal cooling and the potential for a
near surface temp inversion to set up.  If the storms get here after
that happens, we may see more of an elevated storm threat.  On the
other hand, should the storms arrive earlier, which is possible if a
large cold pool is generated, then these storms would have better
access to lingering instability.

Much of the machine learning guidance (CSU GFS and HRRR Neural
network) suggest the highest probabilities of severe weather to
remain across eastern MO/southern IL/W Ky with decreasing
probabilities as you head eastward toward the I-65 corridor.  Given
the CAM solutions and ML probabilities, agree with the upgrade to an
wind driven enhanced across western KY with a careful expansion of
the slight eastward to the I-65 corridor.  Given the modest
instability across our region and forecast low-level shear profiles,
wind damage looks to be the primary weather hazard with this
activity.  However, as with any QLCS, spin ups within any bowing
segment (especially at bow apexes) are certainly possible. Isolated
hail would also be possible, but the hail threat would decrease
rapidly by mid-late evening with the loss of instability.  Current
thinking is that our "show" would be in the 00-07Z time frame.
Overall confidence in the timing remains pretty good, but we`re
still going to account for a 1-2 window either side of that in case
we get a stronger cold pool to develop pushing convection eastward
quicker.

We expect to be post-frontal by sunrise Friday with perhaps some
lingering showers trailing behind the front over eastern KY.  We`ll
see a drying trend in the sensible weather.  Highs on the day will
range from the mid 60s over southern IN to the upper 60s/near 70
across much of KY.  Continued drying and partial clearing of skies
is expected for Friday night with lows dipping into the upper
30s/lower 40s over southern IN/northern KY with low-mid 40s over
southern KY.

Saturday through Sunday Night...

Current forecast ideas for the weekend haven`t changed all that much
with this forecast cycle.  The weekend still looks to be dry and
much cooler as high pressure builds into the region from the W/NW.
Highs Saturday look to top out in the 60-65 degree range in most
areas.  Some light precip may slide across the far southern part of
KY Saturday night and into Sunday morning as an upper level wave
pushes through.  Lows will range from the upper 30s across southern
IN and northern KY with lower 40s expected south of the Parkways. If
skies end up being more clear that forecast, we could have some
threat of frost across our northern areas. Sunday will see slightly
cooler temperatures with highs ranging from the upper 50s to the
lower 60s.  Lows Sunday night will dip into the upper 30s to around
40 in most locations.

Monday through Wednesday...

Latest suite of data suggests that Monday looks to be a bit drier
than in previous forecasts.  However, we`ll see precipitation
chances creep back up on Tues/Wed with a wave dropping through the
region.  Fairly good signal in the models here for the Tue/Wed
system which will allow us to keep good forecast continuity here.
Highs Monday look to warm a bit over Sunday with readings in the low-
mid 60s with overnight lows in the lower 40s.  Highs
Tuesday/Wednesday look to warm back into the upper 60s to the lower
70s with overnight lows in the upper 40s.

&&

.AVIATION /00Z TAFS THROUGH 06Z FRIDAY/...
Issued at 719 PM EDT Wed Apr 17 2024

Basically a wind forecast for most of the valid TAF period as a dry
cold front moves through the Ohio Valley. Decent wind surge still
ongoing with gusts solidly over 20 kt as winds veer from SW to WNW.
Expect the gusts to lay down fairly quickly after sunset, but a more
gradual diminishing trend to go light/variable after midnight. After
a brief period of light SE winds Thu morning, we`ll see more steady
S-SW wind in the afternoon with speeds near 10 kt.

Line of storms will be approaching around sunset Thursday, but
timing will depend on the evolution of the MCS, which remains
uncertain. It`s close enough to the end of the 24 hr TAF that it
will not be included at this issuance, but it does impact the SDF
planning period. At this point will run a PROB30 for thunderstorms
in the evening, with the main limiter being the exact timing of
impact.

&&

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

&&

$$

UPDATE...RAS/KDW
SHORT TERM...KDW
LONG TERM...MJ
AVIATION...RAS