780
FXUS63 KLMK 041414
AFDLMK

Area Forecast Discussion
National Weather Service Louisville KY
1014 AM EDT Fri Apr 4 2025

.KEY MESSAGES...

- Ongoing historic and possibly catastrophic flooding event
continues today through the weekend.  Heed any flood warnings issued
as this will be life threatening flooding across much of Kentucky
and southern Indiana through this weekend.

- Severe threat today will lift north and west to primarily areas in
western Kentucky.  Saturday will have the return of the severe
weather threat through much of the Ohio River valley.

- Drier conditions expected by Monday and another opportunity of
rain moves in late Wednesday night through Friday.

&&

.UPDATE...
Issued at 1013 AM EDT Fri Apr 4 2025

Morning surface analysis reveals a warm frontal boundary lifting
northward through the region.  The front is currently located along
the WK/BG Parkway corridor.  Temps south of the boundary are in the
low-mid 60s with temps north of the front in the lower 50s.  A band
of convection is accompanying the warm front as it lifts northward.
Most of this convection is on the cool side and elevated in nature.

Over the next 1-2 hours, we expect this band to continue to lift
northward promoting a heavy rainfall/flash flood threat across
mainly north-central and east-central KY (along and north of the
WK/BG Parkways).  Individual cells within the band will move east to
west while the overall band will transverse northward in time.
Ground truth precipitation amounts with this activity are generally
in the 0.5 to 0.75 inch/hr range.  So a general 1-2 inches of
rainfall could fall north of the Parkways this morning and into the
afternoon hours.

Focusing on the afternoon, warm frontal boundary is forecast to lift
northward, probably getting into southern IN and just north of the
Ohio River.  Across southern KY, combination of warm advection and
partly sunny skies will allow temperatures to soar into the lower to
possible middle 80s along the KY/TN border, with areas between the
WK/BG Parkways and the Cumberland Parkway getting into the mid-upper
70s.  Temperature forecasts along the river and points north are a
little more difficult to pin down depending on how far north the
front moves.

With the increase in afternoon temperatures and dewpoints remaining
in the 60s, we should see a bit of instability develop.  This could
result in additional thunderstorm development in the warm sector.
Model soundings from the HRRR suggest an instability/shear profile
supportive of supercells.  The HRRR is more aggressive than the 3K
NAM which has similar profiles, but has a bit more capping down
around 850 which could hamper development.  Should convection fire,
large hail and isolated tornadoes would be the main severe weather
hazards in the warm sector.  Will continue to monitor this situation
carefully this morning/afternoon.

&&

.SHORT TERM /THROUGH SATURDAY/...
Issued at 238 AM EDT Fri Apr 4 2025

06Z surface and upper air analysis shows a large upper low in
the desert southwest and the jet stream with strong winds
extending from the low through the central plains to the Great
Lakes which is bringing a river of upper level Pacific moisture.
A 700 mb shortwave trough is providing lift for the storms, a
50 kt low level jet is bringing increased moisture transport,
and a stalled out front roughly along the Kentucky-Tennessee
line is leading to another round of thunderstorms and heavy rain
extending from southwest Kentucky through southwest Ohio.
Kentucky mesonet sites have reported 2-6 inches of rain over the
last 24 hours and numerous flash flood warnings are in effect
across central and northern Kentucky.

Forecast trends for today are showing the warm front lifting
northward through Kentucky and trying to make it to the Ohio river
valley by late in the day.  This should put much of the state in the
warmer air and also lift the training area of showers and storms
northward to along the Ohio River Valley.  South of the front we may
see some peaks of sun especially the further south you are and this
could lead to areas of higher instability to fuel isolated
thunderstorms by late this afternoon.  The better severe weather
setup will be in western Kentucky where the instability and shear
will be higher however in central Kentucky if we can get some
sunshine this will help to increase the instability as CAPE values
could reach to over 3000 J/kg and 0-6 bulk shear of 50 kts will give
any storms a good environment to produce hail, strong winds, and
isolated tornadoes.  Flooding threat will continue especially along
the Ohio river valley as PW values will be anomalously high at
1.5- 1.75 inches and EFI having Euro ensembles members at 0.95
with shift of tails at 2 gives high confidence of a large
precipitation event along the Ohio river valley today. NBM
probabilities of greater than 2 inches of rain in the next 24
hours is at 50%.

Major flooding continues through the weekend as Saturday may bring
some of the highest 1 day totals of rain through much of the region
which will compound the flooding that has occurred from what
rain we received since Thursday and Friday. Severe weather from
Friday night in the form of a squall line to the west will move
across the state during the night into Saturday morning and
threats of gusty straight line winds and QLCS nocturnal
tornadoes can`t be ruled out. This line of thunderstorms will
shift the stationary front to the south and basically stall in
central Tennessee. This should lead to much of the area in the
more stable airmass and the severe threat subsides during the
day on Saturday. With the upper level pattern basically being a
moisture conveyor belt from Texas to the Great Lakes we will see
all day rain and storms through the day on Saturday. NBM
probabilities of receiving greater than 4 inches in the 24 hour
period of Saturday are quite high at 30 to 40% and even
receiving 6 inches is in the 5-10% range. Additional totals of
rain from Friday through Sunday morning could be another 4-8
inches. It bears repeating...this is a historic, catastrophic,
and life threatening flood setup. EFI index has 0.9 and shift of
tails at 2 through much of central Kentucky which shows the
European ensembles are in good agreement of another anomousoly
high precipitation event on Saturday.

&&

.LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/...
Issued at 238 AM EDT Fri Apr 4 2025

On Sunday the upper wave should move into the southeast CONUS
and a sweeping cold front should finally move the axis of
moisture out of the Ohio river valley. Drier conditions are
expected by Sunday afternoon.

We should see a couple of dry and cooler days on Monday and Tuesday
as the trough will usher in a colder airmass from the Great Lakes
and we could see below freezing lows to start the day on Tuesday.
Long range ensembles are showing northwesterly flow continue into
the mid week with another trough coming in that could lead to more
rain and thunderstorm chances from Wednesday night through
Friday.

&&

.AVIATION /12Z TAFS THROUGH 18Z SATURDAY/...
Issued at 644 AM EDT Fri Apr 4 2025

A wavering frontal boundary, and multiple surges of moisture
associated with surface low pressure will continue to keep a messy
forecast and deteriorated conditions over the TAF sites. Expect
continued waves of showers and thunderstorms through this TAF cycle,
with best timing highlighted in this latest issuance. Do expect to
see some IFR this morning before improvement occurs this afternoon
and evening as a brief warm sector gets established over our area.
Showers and storms then set back in this evening into tonight with
ceilings likely deteriorating again. Brief vis reductions into IFR
are expected with any heavier shower or storm.

&&

.LMK WATCHES/WARNINGS/ADVISORIES...
KY...Flood Watch through Sunday morning for KYZ023>043-045>049-
     053>057-061>067-070>078-081-082.
IN...Flood Watch through Sunday morning for INZ076>079-083-084-
     089>092.

&&

$$

UPDATE.......MJ
SHORT TERM...WFO DDC
LONG TERM....WFO DDC
AVIATION.....BJS