Severe Thunderstorm Warning 129, NWS Louisville, KY

Area Forecast Discussion
National Weather Service Louisville KY
338 PM EDT Thu Apr 10 2025

.KEY MESSAGES...

* Isolated strong to severe storms will be possible this afternoon
  and evening, especially across south-central Kentucky.

* Drier conditions with warming temperatures are expected this
  weekend.

* A low-medium confidence chance for strong storms arrives next
  Monday. Gusty winds and hail are the primary severe threats.

&&

.SHORT TERM /THROUGH SATURDAY NIGHT/...
Issued at 337 PM EDT Thu Apr 10 2025

An upper level shortwave will continue to rotate southeast over the
Mid-MS and Lower OH Valleys this afternoon, bringing very cold (-26
C) mid-level air over the region. Though low-level moisture is
modest, strong insolation has warmed sfc temperatures into the mid
60s to lower 70s. MLCAPE appears set to peak at around 1000 J/kg
over central KY and far southern IN through mid-evening.

A cluster of convection has already developed along a weak cold
front in southern IL and southeast MO, with an isolated thunderstorm
now over western KY ahead of the main cluster. This activity will
spread east-southeast through central KY this evening. Additional
updrafts may develop along the convective outflow/cold pool, with
storms increasingly organizing into a short line. Deep-layer shear
of 25-30 kts is marginal for storm organization. But given the very
steep lapse rates through a deep layer, and very cold temperatures
aloft, the environment appears supportive of both isolated damaging
wind gusts and isolated large hail. Storms will be fairly slow
moving to the E/SE due to weaker steering flow aloft. Deep-layer
shear is strongest (30 kts) across south-central Kentucky, with
notably weaker mid-level winds further north. Therefore, have
coordinated with SPC and neighboring NWS offices on a Severe
Thunderstorm Watch for south-central KY. This area is more favorable
for updraft organization, and therefore large hail/wind potential.
Locally strong gusts and hail will still be possible north of the
Watch area.

Convection will weaken after 00Z due to waning instability, but
scattered showers will remain possible overnight. The mid/upper
level trough axis rotates overhead tonight into Friday morning, with
lingering shower activity confined to just south-central KY after
12Z Friday. Friday morning will be cool and cloudy, with a north
wind and lows around 40-45 degrees.

Clouds will take their time clearing Friday afternoon and evening,
but the trend looks positive here as ridging begins to nose in from
the west. Overall, looks like a partly cloudy afternoon with highs
in the 50s.

The first part of the weekend looks cool and pleasant. High pressure
gradually builds east across the area through Saturday night. This
does raise concerns for frost both Friday night and Saturday night,
which could impact sensitive early vegetation. Lows in the low to
mid 30s look possible for much of the area. Other than the chilly
start, Saturday looks like a nice Spring day with afternoon highs in
the mid 50s to around 60 degrees.

&&

.LONG TERM /SUNDAY THROUGH THURSDAY/...
Issued at 337 PM EDT Thu Apr 10 2025

Sunday and Sunday Night...

A warming trend is expected during the second half of the weekend as
upper-level ridging builds over the Mississippi and Ohio Valleys. A
shortwave disturbance moving into northern Plains on Sunday will
promote sfc cyclogenesis over the upper MS valley. Between this low
pressure and high pressure over the northern Gulf, southerly flow
should boost temperatures into the mid-to-upper 60s and lower 70s
across the region Sunday afternoon. All in all, Sunday should be a
pleasant day weather-wise with light south winds and mostly sunny
skies.

Sunday night, a west-southwesterly LLJ will develop over the region
ahead of the approaching mid-level shortwave. This will bring some
moisture into the area, and clouds will increase Sunday night.
However, moisture is not expected to be nearly as rich as last
week's system, with ensemble mean PW values rising to around 1-1.1"
Monday morning. Persistent southerly flow overnight Sunday night
will keep temperatures milder, with lows only expected to fall into
the 50s in most locations.

Monday and Monday Night...

Monday into Monday night, the aforementioned upper trough and sfc
front will move through the Ohio Valley. In previous model runs,
there were minor timing discrepancies between the different ensemble
suites, with the GFS generally a bit slower than the ECMWF. Initial
analysis of the 12Z data suggests better model agreement on timing
of FROPA, which will have an impact on shower/storm chances Monday
afternoon and evening. Forecast soundings for next Monday afternoon
show much of the moisture increasing in the low levels, with cooler
and drier air aloft allowing for steep mid-level lapse rates within
an elevated mixed layer. As the previous discussion noted,
hodographs show primarily speed shear, and given the EML and steep
mid-level lapse rates/dry air, would expect hail and gusty winds to
be the main severe threats. There is quite a bit of uncertainty with
this event, as the overlap between the best forcing and the best
instability is quite narrow, and there will be quite a bit of mid-
level capping to overcome.

Fortunately, this system will be quick-moving, with ensemble mean
QPF amounts only around 0.10-0.25" at this time. As a result, any
additional rainfall Monday is not expected to exacerbate ongoing
hydro/flooding issues.

Tuesday through Wednesday Night...

Behind Monday's system, upper troughing will settle across the
eastern CONUS with NW flow moving over the Ohio Valley. This should
bring another period of relatively calm weather with cold advection
dropping temperatures back below normal on Tuesday. Gusty winds
would be expected on Tuesday, especially given steep low-level lapse
rates in the post-frontal environment. Otherwise, dry weather is
expected through next Wednesday, with the next potential system
arriving next Thursday.

&&

.AVIATION /18Z TAFS THROUGH 00Z SATURDAY/...
Issued at 206 PM EDT Thu Apr 10 2025

Sct SHRA and TSRA have already developed just upstream in portions
of southeast MO and southern IL, and this activity is moving
southeast ahead of an approaching mid-level shortwave trough. Sct
TSRA looks possible at the southern IN and central KY terminals
mainly between 21-03Z this evening. Brief TSRA impacts can be
expected, but expected coverage limits confidence in timing.

After 02-03Z tonight, expect lingering sct SHRA with lowering
ceilings. Prevailing W/NW flow this afternoon and evening will
eventually veer N/NW early Friday morning. A period of low ceilings,
including IFR and low-end MVFR, looks likely between 06-17Z Friday.
NNE winds will increase to around 10-15 kts on Friday.

&&

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

&&

SHORT TERM...EBW
LONG TERM...CSG
AVIATION...EBW

Hazardous Weather Outlook
National Weather Service Louisville KY
356 PM EDT Thu Apr 10 2025

INZ076>079-083-084-089>092-KYZ023>025-028>043-045>049-053>057-
065>067-112000-
Orange-Washington IN-Scott IN-Jefferson IN-Dubois-Crawford-Perry-
Harrison IN-Floyd-Clark IN-Hancock-Breckinridge-Meade-Hardin-Bullitt-
Jefferson-Oldham-Trimble-Henry-Shelby-Franklin-Scott KY-Harrison KY-
Spencer-Anderson-Woodford-Fayette-Bourbon-Nicholas-Nelson-
Washington KY-Mercer-Jessamine-Clark KY-Larue-Marion-Boyle-Garrard-
Madison-Taylor-Casey-Lincoln-
356 PM EDT Thu Apr 10 2025 /256 PM CDT Thu Apr 10 2025/

This Hazardous Weather Outlook is for portions of southern Indiana
and central Kentucky.

.DAY ONE...Tonight.

River flooding will continue to pose a threat to the area. Do not
approach or drive through floodwaters!

This evening, scattered showers and thunderstorms will move across
the region. A few of these storms could be capable of producing
strong winds and/or small hail.

.DAYS TWO THROUGH SEVEN...Friday through Wednesday.

There is low to medium confidence in strong to severe storms Monday
afternoon and evening. Gusty winds and hail are the primary severe
weather hazards.

.SPOTTER INFORMATION STATEMENT...

Spotter activation may be needed.

GENERAL STORM MOTION OF THE DAY:

Storms will move east at 10 to 20 mph.

Any users of this storm motion must be aware that thunderstorm activity
can be erratic and constantly evolving.  Please use this with caution
and be prepared for changing conditions.

&&

More information, along with other weather, hydrological and
climate information can be found, at weather.gov/louisville.

KYZ026-027-061>064-070>078-081-082-112000-
Ohio-Grayson-Butler-Edmonson-Hart-Green-Logan-Warren-Simpson-Allen-
Barren-Monroe-Metcalfe-Adair-Russell-Cumberland-Clinton-
256 PM CDT Thu Apr 10 2025

...SEVERE THUNDERSTORM WATCH 135 IN EFFECT UNTIL 9 PM CDT THIS
EVENING...

This Hazardous Weather Outlook is for portions of southern Indiana
and central Kentucky.

.DAY ONE...Tonight.

Scattered thunderstorms are expected through the evening hours. Some
storms could be strong to severe. The main threats are isolated
damaging winds and large hail.

River flooding will continue to pose a threat to the area. Do not
approach or drive through floodwaters!

.DAYS TWO THROUGH SEVEN...Friday through Wednesday.

There is low to medium confidence in strong to severe storms Monday
afternoon and evening. Gusty winds and hail are the primary severe
weather hazards.

.SPOTTER INFORMATION STATEMENT...

Spotter activation may be needed.

GENERAL STORM MOTION OF THE DAY:

Storms will move east at 10 to 20 mph.

Any users of this storm motion must be aware that thunderstorm activity
can be erratic and constantly evolving.  Please use this with caution
and be prepared for changing conditions.

&&

More information, along with other weather, hydrological and
climate information can be found, at weather.gov/louisville.

EBW

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