651
FXUS63 KLMK 281829
AFDLMK

Area Forecast Discussion
National Weather Service Louisville KY
229 PM EDT Fri Mar 28 2025

.KEY MESSAGES...

* Warm weather continues over the weekend, and widespread light to
  moderate showers and few non-severe storms are expected Saturday
  night.

* Confidence continues to increase for strong to severe storms
  Sunday night, which will be capable of all severe hazards (wind,
  hail, tornado, locally heavy downpours).

* Another strong low pressure system could bring windy conditions to
  the region Wednesday, and thunderstorms, possibly strong,
  Wednesday into Wednesday night.

* Additional showers and storms may continue into Thursday and
  Friday, leading to significant rainfall totals by the end of the
  week.

&&

.SHORT TERM /THROUGH SATURDAY NIGHT/...
Issued at 228 PM EDT Fri Mar 28 2025

Currently, ample atmospheric mixing and WAA have allowed for
temperatures to warm into the upper 70s and low 80s and winds to
gust up to 35mph. These conditions will continue until sunset when
the nocturnal inversion will begin to settle the winds for the
overnight period.

A trough is approaching the TN/OH Valleys from the ArkLaTex. This
trough will increase mid-upper level sky coverage from southwest to
northeast overnight. Broken skies and continued light southwesterly
flow bringing increased dew points will prevent cooling overnight.
Low temperatures are expected to fall into the upper 50s and low
60s.

Saturday, the trough is forecasted to be over the TN Valley and the
40-45kt LLJ will push east over the region. This will help promote
scattered light showers in the mid morning over the western portions
of the region. Through the day these showers will track east and
covering most of the region with scattered showers in the afternoon.
As the column saturates during the day, coupled with the LLJ, gusty
winds up to 30mph will be possible. High temperatures are expected
to be in the mid-upper 70s and flirting with 80 in some spots.

Saturday night, the trough will move over the region, bringing
better forcing and shear to present moisture. This will result in
scattered moderate showers and storms. Storms could bring gusty
winds, but are not expected to be severe. Low temperatures Sunday
morning will be similar to Saturday morning in the upper 50s and low
60s.

&&

.LONG TERM /SUNDAY THROUGH THURSDAY/...
Issued at 228 PM EDT Fri Mar 28 2025

Sunday - Sunday night...

An impactful spring storm system is still forecast to bring severe
storms to the region by Sunday night.

The daylight hours on Sunday will be mostly cloudy with scattered
showers and a few low-topped thunderstorms in warm advection with
shallow moisture below 700mb. South winds gusting to 25-30 mph will
bring warm, moist air northward ahead of the incoming storm system.

Sunday night the Ohio Valley will be beneath the right entrance
region of a northern jet max from the Great Lakes to New England,
and the left exit region of a Pacific jet streaming eastward to the
lower Mississippi Valley. A 500mb shortwave trough will swing
through the Plains and into the Great Lakes with a speed max
advancing from the Ozarks Sunday afternoon to Indiana by late
evening. The low level jet`s strongest speeds will be from Tennessee
to Ohio, and at the surface a Midwestern low will cross Michigan,
swinging it trailing cold front into the middle/upper Ohio Valley by
sunrise Monday.

While clouds and showers may limit instability during the day
Wednesday, this is a strongly dynamically forced system that will
still have sufficient CAPE to work with in a narrow band of surface-
based instability just ahead of the incoming synoptic surface
boundary. Storms that erupt from Illinois to Arkansas Sunday
afternoon are expected to congeal into a line as they move into the
Ohio Valley, with organized convection supported by strong deep
layer shear, MUCAPE around 1000-1500 J/kg, and precipitable water
values in the 1.25-1.50" range. LREF-NH ensemble joint probabilities
show a 60-70% chance of bulk wind shear greater than 40kt coincident
with MUCAPE > 1000 J/kg.  Shear vectors angled slightly off the
surface boundary suggest some bowing segments will be possible
within the QLCS.

Though some model data suggest the possibility of a weak, shallow
surface-based stable layer overnight, there will still be a ribbon
of potential SBCAPE as the storms move in. Strong winds will be
possible given the plentiful atmospheric wind energy and the
potential for bowing line segments. Strong low level shear,
including 0-1km SRH around 250 m2/s2, presents the possibility of
tornadoes in any sections of the line that can orient themselves
more perpendicular to the 0-3km bulk shear vectors. eSTP values
support the idea of weak (but still dangerous!) QLCS-type tornado
spin-ups.

The overnight timing of these storms adds another layer of concern.
People in southern Indiana and central Kentucky should have a way to
receive warnings while asleep Sunday night.

The line of storms will be progressive and is expected to move
cleanly through the region, minimizing widespread flood impacts.
Having said that, warm cloud depths and high PWAT will allow the
storms to be efficient rain producers and will still generate heavy
downpours.

Monday-Tuesday...

Once the showers and storms move off to the east early Monday
morning we`ll have a break from the stormy weather as a long north-
south ridge of high pressure slides from the Plains to the East
Coast.

Wednesday-Friday...

The next seasonably strong surface low will cross the upper Midwest
and upper Great Lakes Wednesday-Wednesday night. Surface winds will
be strong and gusty here on Wednesday, and mid/upper support with
this system may actually be stronger than the Sunday night system.
EFI is showing slightly unusual CAPE-Shear magnitudes, but the main
area of best instability is currently expected to remain just to our
south and southwest. Most recent ML progs from NSSL and CSU have the
greatest severe chances over the lower MS Valley from western
Kentucky to Louisiana, possibly hinting at another set-up where
storms initially fire to our west and then move in as a line. Still
too early to put any specifics on it, but residents of southern
Indiana and central Kentucky should keep in mind that after Sunday
night`s storms, more strong to severe storms (we`re already
outlooked in SPC`s Day 6 forecast) are a possibility Wednesday night.

Of some additional concern is that last night`s ECMWF and LREF-NH
depictions, and now this morning`s GFS, show Wednesday night`s cold
front slowing its forward progress, possibly as a result of another
wave riding up the boundary from the southwest, leading to a
prolonged period of showers and storms continuing into Thursday and
Friday, raising the question of heavy rain totals. NAEFS and HEFS
(less so on the GEFS) do show a consistent upward trend in Ohio
tributary river levels late next week.

&&

.AVIATION /18Z TAFS THROUGH 00Z SUNDAY/...
Issued at 123 PM EDT Fri Mar 28 2025

VFR conditions will continue through the TAF cycle. currently, clear
skies have allowed for ample mixing to bring down gusty winds up to
25kts. These wind gusts will continue until sunset when winds will
settle for the night. The LLJ begins to ramp up overnight bringing
in LLWS from 6Z until 13Z. Overnight, mid-high level clouds will
stream overhead from the southwest as a trough approaches the
region.

&&

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

&&

$$

SHORT TERM...SRW
LONG TERM...13
AVIATION...SRW