LMK issues Area Forecast Discussion (AFD) at Apr 1, 3:39 AM EDT351
FXUS63 KLMK 010739
AFDLMK
Area Forecast Discussion
National Weather Service Louisville KY
339 AM EDT Tue Apr 1 2025
.KEY MESSAGES...
* Another strong low pressure system is expected to bring windy
conditions to the region Wednesday, and strong-to-severe
thunderstorms Wednesday into Wednesday night. Damaging winds and
spin-up tornadoes are the primary threats with severe weather
Wednesday.
* Additional showers and strong storms are expected to continue from
Thursday into the weekend. A high-impact, major rainfall and
flooding event across the lower Ohio and Tennessee valleys will
bring major (and potentially life-threatening) flooding.
* Widespread minor to moderate river flooding expected, major river
flooding is possible.
&&
.SHORT TERM /THROUGH WEDNESDAY NIGHT/...
Issued at 338 AM EDT Tue Apr 1 2025
Today...
This morning, nighttime microphysics satellite imagery shows the
back edge of the post-frontal stratus slowly pushing off to the
southeast. Cool temperatures are noted across the region, with
temperatures under clear skies in the 30s while areas where low
clouds linger remain in the low 40s. Later this morning, lingering
low clouds will begin to scatter out, with mostly sunny skies
expected for the afternoon and evening hours. An inverted sfc
pressure ridge will cross the region later today, causing winds to
veer from the northeast to the east, with wind speeds generally
remaining at or below 10 mph. While the better warm advection should
hold off until tonight, sunshine should help temperatures warm into
the upper 50s and lower 60s across southern IN and northern KY, with
low-to-mid 60s expected this afternoon across southern KY.
Tonight into Early Wednesday...
Within deep SW flow aloft, an upper level shortwave will begin to
eject across the central Plains tonight, triggering convection
across the Missouri Valley. This feature will also nudge sub-990 mb
low pressure farther to the east, with substantial pressure falls
occurring across the Midwest and Mississippi Valley. As a result, a
stronger pressure gradient will lead to strengthening SE winds
overnight, with a veering profile in the low-to-mid levels
suggestive of strong warm advection. Temperatures should fall into
the 40s and low-to-mid 50s initially after sunset; however, a
warming trend is likely toward dawn Wednesday as return flow really
ramps up. There is a low-confidence chance for some rain showers in
the pre-dawn hours Wednesday as higher low-level theta-E surges into
the region. More pronounced forcing mechanisms will remain to the
north of our area; however, if a stronger updraft were to occur, an
elevated thunderstorm cannot be ruled out given mid-level lapse
rates around 7.5 deg C/km an around 1000 J/kg MUCAPE, particularly
over southern IN.
Wednesday Gusty Winds and Warm Temperatures...
By the late morning hours on Wednesday, a strong pressure/height
gradient will be over the region, with 00Z HREF mean 850 mb winds of
60-65 kt overhead. While poor sfc-850 mb lapse rates and some low
clouds should limit how much of this momentum mixes down, there is
fairly high confidence in at least advisory level wind gusts, with
the NBM probabilities of 24-hr max wind gusts over 40 mph exceeding
90% in our typically gusty areas.
Strong SSW flow will send temperatures surging on Wednesday, with
strong warm advection taking place as our area will be well within
the warm sector. While a stratocu layer should limit warming
somewhat, would still expect temperatures to make it into the upper
70s and low-to-mid 80s Wednesday afternoon, approaching record
levels for April 2nd.
Wednesday Evening/Wednesday Night Severe Storms...
The incredibly potent return flow which will take place late tonight
into Wednesday morning will condition the atmosphere for strong to
severe storms Wednesday evening into Wednesday night. Surface
dewpoints are expected to rise into the low-to-mid 60s by Wednesday
afternoon, resulting in at least 1000-2000 J/kg SBCAPE. Some progs
like the 00Z GFS even have pockets of 2000+ SBCAPE with upper 60s
dewpoints, though this may be a bit overdone. With this being said,
model soundings also show quite a bit of CIN via a mid-level capping
inversion in the 850-700 mb layer. This CIN should gradually erode
from west to east Wednesday afternoon and evening; however, some
progs like the 00Z HRRR/03Z RAP appear to be too aggressive in
developing robust convection within the warm sector. If anything
does initiate late Wednesday afternoon, it should remain discrete
given the aforementioned cap as well as a more favorable deep-layer
shear orientation.
The more likely convective evolution seems to be what is depicted in
the NAM solutions, where the better upper jet dynamics and sfc
boundary trigger convection Wednesday afternoon across AR, MO, and
IL. This convection should grow upscale into either a broken QLCS or
disjointed multicell clusters, gradually pushing toward western KY
and southwest IN Wednesday evening. Since the upper shortwave which
triggers convection will be lifting well off into Canada Wednesday
night, it appears that storms will be reliant upon convectively-
induced surges to push toward central KY and southern IN Wednesday
night. Recent trends have been farther NW with where the sfc
boundary stalls Wednesday night, and there is increasing potential
that storms may not reach our Lake Cumberland counties until around
dawn Thursday (if they make it there at all!). Regardless, the most
likely timing for any strong to severe storms now looks like it will
be after 00Z Thursday in our area, lingering until around dawn on
Thursday.
As far as severe hazards are concerned, think that damaging winds
and brief spin-up tornadoes will be the main hazard within any kind
of QLCS. If multicell clusters are able to remain somewhat discrete,
these would carry a greater threat for large hail and longer-track
tornadoes.
&&
.LONG TERM /THURSDAY THROUGH MONDAY/...
Issued at 338 AM EDT Tue Apr 1 2025
Thursday - Sunday...
****MAJOR FLOODING (POTENTIALLY LIFE-THREATENING) EXPECTED****
The long term will begin with southwesterly flow aloft. The trough
over the northern Great lakes will continue to push northeast. The
cold front associated with the system will stall near the Ohio
River. This southwesterly flow pattern is reminiscent of
northwesterly flow with small shortwave disturbances and vort lobes
that are enough to kick off another round of storms. That is exactly
what it is looking like for Thursday, Friday, and Saturday. The
southwesterly flow will amplify into a ridge through the weekend and
small shortwave disturbance, CVA, and a 45-55kt LLJ will move
through the region bringing daily chances for strong to severe
thunderstorms. Damaging winds, hail, and a brief tornado will be
possible.
Amongst ensembles and the EFI there is good agreement that there
will be ample CAPE and speed shear. Gulf moisture will remain over
the region with PWATs near max climatology of 1.6-1.9 inches and
dew points in the mid 60s.
With multiple rounds of convection through the weekend, extreme
rainfall totals are expected to bring significant areal, flash, and
river flooding. Life-threatening flooding is possible in some areas.
The ECMWF EFI continues to show high values and the shift of tails
of 2, which means there is high confidence for anomalous QPF and
some ensemble members show extreme QPF values. Most guidance shows
the largest swath of QPF along the Ohio River, varying to the north
or south slightly. There will likely be a tight gradient of QPF to
the southeast. In the largest swath of QPF, we are currently looking
at 8.5-11.0 inches of rain through the weekend, with additional
accumulations possible in localized areas. The GFS and other models
suggest even larger amounts of 12+ inches. In our southeastern
counties, accumulations should be 3-6 inches.
To put these QPF values into historical reference the 6-day total of
the March 1997 flood was 13.69 inches in Louisville, following is
the March 1964 flood with 12.31 inches, and then the January 1937
flood with 10.31 inches. If these QPF forecasts verify, this will be
a rainfall and potential flooding of historic proportions.
Widespread minor and moderate flooding is expected along all rivers.
There is a 30% chance of exceeding major flood stage along rivers in
central and northern Kentucky and southern Indiana. If you live
along a river or in an area that can experience river flooding, it
is time to prepare now. Rain will begin Wednesday and multiple
rounds will bring rain through Sunday.
With the cold front stalled over the region and a strengthening
upper ridge, there will be quite a temperature gradient across the
region. Our southeast may see high temperatures in the low-mid 80s
and the northwest may see the upper 60s and low 70s.
Monday - Mid Next Week...
Troughing over the desert southwest will move east over the southern
Plains and potentially phase with a closed low over southern Canada.
This will be the feature to push the stalled front and relentless
rain out of the region to the east. High pressure and quieter
weather will build in behind. Temperatures look to be below normal
for lows and slightly below normal for highs.
&&
.AVIATION /06Z TAFS THROUGH 12Z WEDNESDAY/...
Issued at 128 AM EDT Tue Apr 1 2025
The back edge of the MVFR stratus layer is just northwest of SDF and
BWG at this hour. Recent satellite imagery suggests that SDF should
clear out in the next 1-2 hours; however, model guidance wants to
try to fill back in with MVFR stratus later this morning. Farther to
the east, while there is higher confidence in continued MVFR CIGs at
LEX and RGA, CIGs should be right around 2kft, and may briefly fall
below this threshold later this morning. Between 14-18Z today,
stratus should scatter out, leading to VFR conditions through the
rest of the forecast period. Winds will veer to the east today, with
speeds generally between 6-10 kt. Tonight, low pressure moving
across the Plains will cause winds to increase and veer to the
southeast overnight. LLWS looks likely after 06Z, but will hold off
on inclusion in the forecast for now.
&&
.LMK WATCHES/WARNINGS/ADVISORIES...
KY...Flood Watch from Wednesday evening through Sunday morning for
KYZ023>043-045>049-053>057-061>067-070>078-081-082.
IN...Flood Watch from Wednesday evening through Sunday morning for
INZ076>079-083-084-089>092.
&&
$$
SHORT TERM...CSG
LONG TERM...SRW
AVIATION...CSG
Source:
LMK issues Area Forecast Discussion (AFD) at Apr 1, 3:39 AM EDT---------------
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