455
FXUS63 KLMK 032354
AFDLMK

Area Forecast Discussion
National Weather Service Louisville KY
754 PM EDT Thu Apr 3 2025

.KEY MESSAGES...

- Historic and possibly catastrophic flooding is expected
  across the region through the weekend. Training thunderstorms
  are expected to drop 5-10 inches of total rainfall through
  Sunday across the area. Locally higher accumulations are
  possible.

- Chances for strong to severe storms continue through the day.
  Primary risk area is south of the Western Kentucky Fwy/Blue
  Ridge Pkwy. All severe hazards are possible including
  flooding, damaging winds, hail, and tornadoes.

- Flooding chances linger through the weekend. Please be aware
  of flooding potential and do not drive into flooded areas. The
  depth and speed of flood waters are difficult to determine,
  especially at night. Turn around, don`t drown.

- Drier conditions return Monday and Tuesday with more showers
  and thunderstorms possible Wednesday and Thursday.

&&

.UPDATE...
Issued at 753 PM EDT Thu Apr 3 2025

After coordination with the Storm Prediction Center and WFO Jackson,
we have dropped the Tornado Watch for our south-central KY counties.
The effective warm front has pushed south this afternoon, reinforced
by convective outflow, and is now draped WSW to ENE through Middle
TN and eastern KY. For the central part of KY, that boundary has
shifted far enough south of the TN border to largely eliminate the
tornado threat. The near-sfc layer is stable, with sfc temps in the
upper 50s to lower 60s and a northerly sfc wind.

The main near-term concern over the next 3-6 hours is additional
flash flooding. We do still have elevated instability - MUCAPE on
the order of 500+ J/kg. Latest radar trends show a band of elevated
convection spreading ENE roughly along the Ohio River, but we have
lightning all the way north of Madison, IN as of this writing. The
SSW low-level jet increases over the next 3-6 hours and will
continue to advect copious amounts of moisture across the boundary.
SW to NE training convection will easily lead to additional Flash
Flooding, possibly significant and life-threatening. Latest HREF PMM
guidance shows potential for swaths of 1-2 inches in three hours
across central KY and far southern IN. Cannot rule out localized
totals of 3-4 inches over the next six hours.

&&

.SHORT TERM /THROUGH FRIDAY/...
Issued at 335 PM EDT Thu Apr 3 2025

****SIGNIFICANT SEVERE STORM AND FLOODING THREAT CONTINUES THIS
 EVENING****

Satellite imagery this morning showed the evolution of the ongoing
complex situation across the region. Looking at the macro-scale, a
large synoptic low across eastern Canada is dropping an expansive
cold front stretching from the NE CONUS SW through central KY into
Texas. Northwest flow on the backside of this synoptic low is
pushing cooler air into the central CONUS while southerly flow over
the SE CONUS pushes warm air and copious moisture up from the Gulf.
All of these things are converging upon AR, TN, KY leading to
another active day across the region. Making things a little more
complicated, surface observations show a surface to mid level
mesoscale low across central TX that is enhancing southerly WAA and
frontogenesis between these systems.

These competing air masses are stalling out the movement of the
synoptic scale fronts which are more or less stationary from
northern MS through central TN into eastern KY in a generally west
southwest to east northeast layout. Storms motions parallel to this
boundary sets up an environment where storms can initiate on the
boundary, move along it, then more storms form behind them training
over the same areas repeatedly all day. Add to that the continued
advection of moisture into the area which essentially replenishes
the precipitable water creating a environment conducive to repeated
heavy rainfall. QPF values over the course of the next 24 hours
average around 3-4" with the min-max of the range being at least 1
inch across SE KY and topping out around 3-4 inches across central
and southwestern KY. QPF through Sunday averages around 5-6 inches
cumulative with at least 3 inches on the lower end and 9-10 inches
on the upper end. Flooding (both flash and river) is going to be an
issue, potentially catastrophic flooding is possible.

Continued warm air and moisture advection maintains instability
through the afternoon enabling the development of strong to severe
thunderstorms. High-res CAMs are a little less aggressive with the
northward movement of the front which keeps the strong to severe
potential south of the Western KY Freeway/Blue Ridge Pkwy. Tornado
potential remains active through the afternoon with 0-1km bulk shear
and storm relative helicity above 40 knots and 300 m2/s2
respectively. The convergence of these convective variables is
further south making the greatest tornado chances along the KY/TN
border gradually decreasing as you move north toward Elizabethtown.
The good news is that both SBCAPE and MUCAPE wane as the evening
progresses lowering overall severe potential after sunset. The
boundary lifts a little northward through the night enveloping the
rest of the region in rainfall through tomorrow morning.

&&

.LONG TERM /FRIDAY NIGHT THROUGH THURSDAY/...
Issued at 335 PM EDT Thu Apr 3 2025

**** MAJOR FLOODING (POTENTIALLY LIFE THREATENING) EXPECTED****

As alluded in the previous paragraph the strong Bermuda high to
the east impedes the movement of the synoptic cold front
causing it to stagnate over the OH Valley for the next few days.
A northward surge in the upper level flow brings small breaks
in the precipitation on Friday; however, scattered showers and
thunderstorms continue through Friday. Saturday, a large upper
level low across the SW CONUS finally begins to shove the front
eastward. This is further motivated by a strong surface lee
trough. Unfortunately this strong influx will result in another
day of widespread heavy rainfall Sunday. An additional 3-4
inches are possible (adding up to the total QPF mentioned
previously of 8-10 inches of total precipitation). Fortunately,
instability remains rather lacking, but PWAT values at or above
1.5-2 inches promotes efficient heavy rainfall with 1-2 inch per
hour rates not out of the question. Rain rates and
accumulations Sunday look heavier than what we are seeing today.
The good news is that once this front rolls through, things
look to dry out Monday and Tuesday. 500mb flow turns
northwesterly behind these systems allowing a bit of a break
before another wave rolls through the area Wednesday afternoon
and Thursday bringing more showers and thunderstorms.

&&

.AVIATION /00Z TAFS THROUGH 06Z SATURDAY/...
Issued at 714 PM EDT Thu Apr 3 2025

Periodic thunderstorms and heavy rain will highlight the entire TAF
period for all the terminals and this will be reflected with many
PROB30 statements. Cloud ceilings will fluctuate between MVFR and
IFR through 06Z and IFR flight category will occur when rain showers
or thunderstorms go over the terminal and MVFR flight category will
occur in the periods of time when the rain ends. After 06Z we should
see a large squall line of storms and heavy rain enter from
southwest to northeast and overspread much of southern Indiana and
central Kentucky.  Between 12Z-00Z the greater chances of rain and
storms will occur for HNB, SDF, LEX, and RGA with lesser chances of
rain and storms for BWG as the warm front and better lift will be in
southern Indiana...however isolated strong storms will be in the
forecast around BWG during this time.  Probabilities of MVFR will be
greater in BWG as well (70-80%)...while probabilities of IFR (60-
90%) and possible LIFR (10-20%) categories around HNB, SDF, LEX, and
RGA will be greater during this time especially with the stronger
thunderstorms and heavy rain which could take surface visibilities
to as low as 1-2 SM at times and ceilings to 500 ft or below.
Generally the environmental surface winds will be on the light and
variable side at 5-10 kts but between 12-00Z we could see occasional
thunderstorm wind gusts at 20-30 kts.

&&

.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...EBW
SHORT TERM...BP (WFOEAX)
LONG TERM...BP (WFOEAX)
AVIATION...WFODDC