762
FXUS63 KLMK 121409
AFDLMK

Area Forecast Discussion
National Weather Service Louisville KY
1009 AM EDT Wed Mar 12 2025

.KEY MESSAGES...

* Unseasonably warm and mainly dry through late week.

* A strong storm system will impact the region Friday night through
  Saturday night, bringing multiple rounds of showers and
  thunderstorms.

* Multiple hazards are likely with the weekend system, including
  severe thunderstorms, flash flooding, and strong gradient winds.
  All severe hazards are possible with this system, though
  confidence in hazard threat levels remains low.

&&

.UPDATE...
Issued at 1008 AM EDT Wed Mar 12 2025

Other than some thin cirrus pushing across southwest IN and northern
KY, skies were mostly sunny across the region and temperatures had
warmed into the lower 60s.  Current forecast remains on track for
this afternoon.  We should be a little bit warmer than yesterday
with highs in the upper 70s to near 80.  We probably will break high
temp records at Louisville, Lexington, and Frankfort.  BWG`s record
is 82 and it we`ll be close to that down there.

We`ll have another day of dry air mixdown allowing afternoon RH`s to
drop into the 20-30% range, though some locations may drop below
20%, making any fire behavior a bit more volatile.  We`ll likely see
a number of hot spots show up again today.

&&

.SHORT TERM /THROUGH TONIGHT/...
Issued at 337 AM EDT Wed Mar 12 2025

Another dry day with near-record to record high temperatures expected
across the area. We remain under dry zonal flow aloft and on the
northern fringes of surface high pressure to our south. There is a
weak frontal boundary that is stalling near our northern CWA border
at this hour, however this feature is expected to begin lifting back
north today as a weak warm front. As a result, we`ll see continued
steady S to SW surface winds. Expecting to mix pretty deep again
today, so the gusts in the 20 to 25 mph range will kick up late
morning into the afternoon. Also expecting dew points to fall out
once again as we tap into the very dry hydrolapse above H85. As has
been the theme, went with a blend of NBM 5th percentile and HRRR dew
points, which yields minimum relative humidity values mostly in the
20-30% range this afternoon. Some values will likely dip into the
teens, while others will stay closer to 30%. Regardless, the combo
of continued dry, mild, and occasionally gusty conditions will make
for more volatile fire behavior. Plenty of hot spots yesterday
afternoon on satellite imagery, and expecting more again today.

Will note that one difference for today will be some scattered upper
sky cover moving overhead from mid morning through mid afternoon.
The filtered sunlight could hurt full heating potential just a bit,
and may limit the deepest mixing heights. Still a blend of NBM 95 to
75 percentile temps yields values at or near records for today.
Current forecast would break the ongoing record at SDF/LEX, and fall
just short at BWG. Values should peak in the upper 70s to near 80
for everyone.

Temps may try to fall off fairly quickly after sunset as the typical
cool spots once again decouple. Will likely see some evening
ridge/valley splits, however some thick upper sky cover begins to
move in especially after Midnight. The end result should then be
temps either leveling off or perhaps trending a bit milder toward
sunrise on Thursday. We`ll begin to focus on the upstream shortwave
as we approach sunrise Thursday. Any approaching precipitation
should encounter a pretty dry airmass, but do have some sprinkle
mention just before daybreak in our far SW CWA.

&&

.LONG TERM /THURSDAY THROUGH TUESDAY/...
Issued at 337 AM EDT Wed Mar 12 2025

Thursday - Friday...

A weakening upper low embedded within zonal flow will move across
the Tennessee and lower Ohio valley on Thursday. While there should
be increasing moisture in association with this disturbance, the
antecedent environment will be quite dry, likely limiting total
precipitation amounts with this system. Dry air and cooler mid-level
temperatures will allow for some instability for thunderstorms;
however, shear will be fairly weak, so not expecting anything more
than a few garden-variety thunderstorms during the day on Thursday.
Total precipitation amounts should be less than a tenth of an inch,
except for localized higher amounts in any storms which may develop.

Thursday night into Friday, dry weather will return as ridging and
southwesterly flow aloft builds into the area ahead of a
strengthening system ejecting toward the Rockies. Friday should be
another very warm and dry day, with SSE winds increasing through the
day as the pressure gradient tightens. Depending on how much mixing
occurs, temperatures could reach 80 degrees or even approach record
values Friday afternoon. As winds increase, if enough dry air is
able to mix down from above the boundary layer, critical fire
weather conditions may also be achieved Friday afternoon.

Friday Night - Saturday Night...

By Friday evening, a leading negatively-tilted shortwave is progged
to move from the central Plains north-northeastward toward the upper
Mississippi valley. The associated sfc low with this upper
disturbance will be occluding over eastern NE and western IA, with a
sfc pressure trough/front arcing from NNW to SSE toward the Ozarks
and mid-Mississippi Valley. Along this front, convective initiation
is expected late Friday afternoon west of the Mississippi River,
continuing to the east-northeast Friday evening and into Saturday
morning. As this line of (likely) strong to severe thunderstorms
approaches southern IN and central KY, a strong (60+ kt) southerly
850 mb jet is expected to develop late Friday evening, increasing
low-to-mid level moisture from what will initially be a very dry
layer. How much of this flow aloft makes it down to the surface is
still uncertain and will be dependent on how well boundary-layer
stability can get established during the evening hours. In more well-
mixed locations, BUFKIT momentum transfer shows the potential for 40-
45 kt wind gusts, so there is certainly potential for strong
gradient wind headlines. This threat for strong gradient wind gusts
will linger into Saturday morning as the boundary layer destabilizes.

For the severe storm potential Friday night into early Saturday
morning, with such strong flow expected aloft, ample wind shear and
helicity will be available. Sample soundings show 50+ kt of
effective bulk shear and 35+ kt of 0-1 km shear, which is more than
sufficient for organized severe convection and even supercells. The
uncertainty with this wave of storms lies primarily with near-sfc
moisture recovery and the resultant instability. Most progs get sfc
dewpoints into the mid-to-high 50s ahead of the line of storms,
which is enough for anywhere from negligible SBCAPE to a 300-500
J/kg. With the main pool of greater near-sfc moisture remaining just
west of the region, the expectation remains that convection will
likely be in a weakening state as it moves from the western CWA
toward the I-65 corridor. However, this does not mean that the
severe potential can be dismissed, especially given the magnitude of
shear parameters. Would expect the primary threat with this first
wave to be damaging straight-line winds with spin-up tornadoes also
possible. Showers and storms should continue to weaken east of the I-
65 corridor by around daybreak Saturday, with a lull in
precipitation expected Saturday morning.

A second, likely more expansive wave of precipitation is expected
Saturday afternoon into Saturday night as a second area of sfc low
pressure cuts from SSW to NNE from the lower MS valley to the Great
Lakes. Considerable deepening of this low should take place given
favorable positioning between right entrance region of a northern
jet streak and the left exit region of a southern jet streak. Ahead
of this wave of precipitation, destabilization is expected. While
GEFS/GEPS ensemble mean SBCAPE is only around 500 J/kg, 90th
percentile SBCAPE is around 1500 J/kg, which more closely matches
deterministic progs and is likely a more realistic depiction of
actual instability levels. Wind shear parameters for the Saturday
afternoon/evening wave are more modest, likely due to the fact that
the leading LLJ will be exiting to the north while the secondary jet
will still be south of the area. Still, soundings show around 40 kt
of effective bulk shear, which is sufficient for multicell clusters
and even a few supercells. Effective SRH is on the order of 100-125
m2/s2, much more modest than with the Friday night wave. It is worth
noting that with increasing mid-level dry air during the day on
Saturday, hail parameters are quite impressive, with sig. hail
parameter greater than 1 and large hail parameter greater than 10
(!) in selected soundings. Given the parameter space, can`t rule out
a few tornadoes with the Saturday afternoon/evening wave, but think
that hail and wind look like the primary threats at this time. The
threat area with this wave continues to evolve, but would expect at
least areas from I-65 eastward into eastern KY to be under the gun
with this wave.

Severe storm potential should transition to more of a heavy
rainfall/flash flooding threat during the late evening hours on
Saturday as convection eats up instability. While NBM continues to
suggest that most-likely rainfall amounts should range from 1-2"
across the CWA (which wouldn`t cause too many issues), reasonable
high-end QPF totals are between 3-4", with the heaviest amounts
along and south of the Western KY/Bluegrass Parkways. Localized
higher amounts are possible, especially if training of convective
elements occurs Saturday evening. The greatest threat for river
flooding continues to be along the Green River, with more flash
flooding potential than in the mid-February heavy rain event given
likely rain rates. Precipitation should gradually wind down early
Sunday morning as the sfc cold front presses through the region.

Sunday - Tuesday Night...

The upper trough will move over the region Sunday into Sunday night,
and a few lingering post-frontal showers will be possible during the
day on Sunday. Modest CAA should knock temperatures back toward near
climatological normals for Sunday through Monday, with highs in the
50s and 60s and lows falling into the 30s. Much calmer weather is
expected for the first half of next week as high pressure settles
into the Gulf states Monday into Tuesday. As high pressure moves
toward the Florida panhandle and low pressure develops across the
upper Midwest on Tuesday, deep southwesterly flow will encourage a
warming trend into the middle of next week. The next significant
system looks to move into the region next Wednesday night into
Thursday, though confidence is low in specifics at this time.

&&

.AVIATION /12Z TAFS THROUGH 18Z THURSDAY/...
Issued at 630 AM EDT Wed Mar 12 2025

VFR conditions will continue to prevail through this forecast cycle.
We`ll continue to keep a light S to SE surface wind early this
morning, with a weak frontal boundary stalling over southern IN.
The frontal will then lift back north through this afternoon,
keeping us in steady S to SW flow. Gusts in the 20 to 25 mph range
will pick up late morning through the afternoon along with some
scattered upper clouds. Gusts slacken toward sunset, with increasing
mid and upper sky cover going into early Thursday morning ahead of
the next system.

&&

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

&&

$$

UPDATE.......MJ
SHORT TERM...BJS
LONG TERM....CSG
AVIATION.....BJS