Severe Thunderstorm Warning 37, NWS Louisville, KY

Area Forecast Discussion
National Weather Service Louisville KY
856 AM EST Thu Jan 12 2023

.Mesoscale Update...
Issued at 845 AM EST Thu Jan 12 2023

Broken line of strong to severe storms moving across central
Kentucky this morning, with the SVR threat shifting from hail
earlier to wind and even brief spin-up tornadoes as instability
becomes more sfc-based. Most of the velocity signatures have been
messy, but a few short-lived couplets did prompt two Tornado
Warnings within the past 30-45 min.

Storms are moving into an increasingly favorable environment in
south-central Kentucky, with about 500 J/kg of sfc-based CAPE (but
still about 75 CIN) and effective bulk shear pushing 60 kt. The
eastward progression has been a bit quicker than previously
expected, so the window for SVR might remain open long enough to
extend the SVR threat into the I-75 corridor, with a low but non-
zero tornado threat. Therefore we will expand WW 16 into the rest of
our eastern counties, while clearing behind the line in southern
Indiana and west of I-65 in Kentucky.

&&

.Short Term (Now through Thursday Night)...
Issued at 255 AM EST Thu Jan 12 2023

...Strong to Severe Storms possible Today...

*********************************************************************

Key Messages:

 - Several waves of showers with embedded strong-to-severe
thunderstorms are expected between now and mid-afternoon today.
Damaging winds are the main severe threat, with severe hail (>1")
and an isolated tornado possible.

 - Total rainfall between now and tonight will range from 0.5-1.5"
on average, with isolated 2"+ amounts possible where training of
heavy showers/storms occurs.

 - Temperatures drop Thursday night with lingering moisture expected
to produce a few snow showers by sunrise Friday.

*********************************************************************

Discussion:

Conditions are mild, but quiet across central KY and southern IN at
this hour, though this is expected to change as a cluster of showers
and thunderstorms presently near the confluence of the MS and OH
rivers moves into our vicinity over the next several hours. These
showers and storms are associated with a developing sfc low near the
MO/AR border which will track northeastward into the Ohio Valley
during the day on Thursday. Ahead of the sfc low, a low-level jet
and associated 850- and 925-mb theta-E plumes will surge northward
into the area, preconditioning the atmosphere with additional
moisture and instability. A corridor of PWAT values in excess of 1"
and MUCAPE of 500-1000+ J/kg will stream across the area between now
and sunrise, gradually weakening in magnitude as it moves east of
the I-65 corridor. This should give sufficient fuel to ongoing
convection, with additional new convection also possible along the
leading edge of this moisture/instability surge. With the initial
wave of storms over the next several hours, the near-sfc layer
should be stable, with recent AMDAR soundings from SDF showing much
of the current instability coming from above an elevated mixed layer
at around 800 mb. This would allow for severe hail to be the main
threat with any storms, especially given model soundings showing 0
to -20 deg C layer lapse rates on the order of 8 deg C/km.

After sunrise today, persistent low-level warm/moisture advection
will try to erode the near-sfc stable layer away, especially across
southern KY. There appears to be a window on current hi-res guidance
between 14-18Z where 500-1000 J/kg SBCAPE could be realized for
areas along and south of I-64, with sufficient shear and helicity
(50+ kt. effective bulk shear and 150-200 m2/s2 effective SRH) and
favorable low-level hodographs for an isolated tornado or two. This
will be a narrow window, as the sfc pressure trough will quickly be
veering winds around to W/NW, eliminating the necessary low-level
helicity for tornadogenesis. Once sufficient low-level veering
occurs, the severe threat should transition to exclusively damaging
straight-line winds, which will also be the predominant severe
threat over the course of this entire event. The severe threat will
end from NW to SE as colder NW winds rush in behind the sfc cold
front. The "all clear" should occur shortly after lunch for areas
north of the Parkways, with a lingering low-end severe threat until
just before sunset.

In total, rainfall amounts will range from a half an inch to an inch
and a half on average. However, if any cells/line of storms arrange
themselves parallel to the low-level jet axis, isolated swaths of 2"
or higher are possible due to training. While isolated flooding
issues cannot be ruled out, expect area basins to be able to handle
this amount of rainfall.

After sunset tonight, temperatures will fall steadily through the
40s and into the 30s across the area. Residual low-level moisture
and steep low-level lapse rates will contribute to the advent of a
few rain (and eventually snow) showers, also aided by a fetch off of
Lake Michigan. Hi-resolution data suggests that narrow bands of
moderate precipitation are possible, especially toward sunrise
Friday. However, confidence in placement of any heavier bands is
very low at this time, so will just blanket the region in a 20-30
PoP for rain/snow showers leading into the extended forecast period.

.Long Term (Friday through Wednesday)...
Issued at 250 AM EST Thu Jan 12 2023

Key Messages:

- Lingering snow showers through Friday, lasting into Friday night

- High pressure and pleasant weather this weekend

- Another low pressure system will impact the area on Monday-
Tuesday and bring showers and storms along the cold front

Friday - Friday Night...

Look for a pretty raw day on Friday as gusty NW winds (25 to 30 mph)
and a lingering stratus deck help to keep temps near steady in the
low to mid 30s. With the aid of the winds, wind chills will be in
the 20s. There has been a pretty consistent signal for lingering low
moisture in the 1000-800 mb layer, with some aid from a favorable
and persistent fetch off Lake Michigan to keep the moisture supply
going. Given pretty steep low level lapse rates, and the saturation
up to around -10C through Friday, we'll see scattered snow showers
through the day, with perhaps a few "lake enhanced" (from a moisture
perspective) bands that have been showing up consistently on the
higher res data. Any of those more pronounced and persistent bands
would have some slightly deeper moisture that would saturate just a
bit deeper into the bottom of the DGZ, which will give some slightly
better rates. Still, overall accumulations through the day on Friday
will be tough given temps at or just above freezing. It will take
pockets of briefly heavier rates and/or a few more persistent bands
aided by the moisture fetch. Will continue to call for a dusting
possible in spots through the day, but could see some locally higher
amounts in our far eastern CWA where you start to get some better
upslope enhancement.

As we move into Friday evening and overnight, better chances for
some light accums should occur as temps fall into the 20s. The same
setup persists, but this will be mainly east of I-65 by this time as
we start to dry out west of I-65. Where snow showers linger, could
pick up an additional dusting to half an inch of snowfall,
especially toward the I-75 corridor. Overall, think there is a
chance of a dusting to a half an inch storm total for most east of
the I-65 corridor. However, there is enough of a signal in the
higher res data to expect up to an inch somewhere in a narrow swath
or two between the I-65 and I-75 corridors where that lake enhanced
fetches set up and persist Friday/Friday night. Will have this
reflected in our Prob Snow graphics with an increase in probs for 1".

Saturday - Sunday Night...

Surface high pressure and progressive, but amplified, upper ridging
will dominate the region through the weekend. This will lead to
mostly clear and dry weather with temperatures also recovering
quickly. After Saturday highs a degree or two on either side of 40,
Sunday highs climb back to the upper 40s and low 50s. Saturday night
will still be cold with lows well into the 20s for most, however
will already see milder lows for Sunday night as steady S winds and
increasing sky cover keep things milder.

Monday - Wednesday...

Still looking pretty good for widespread rainfall to overtake the
region through the day on Monday, ahead of a shortwave and the
associated surface low moving into the mid Mississippi River Valley
and upper Midwest. Perhaps we could see a few rumbles of thunder,
but this looks to be largely a rain event. Not concerned about any
stronger storm threat either given that dew points look to remain in
the 40s. Already have categorical pops going for Monday, and expect
a good .5" to .75" for much of the area if current data holds.

We should be drying out from west to east by Tuesday morning with
high pressure and unremarkable zonal flow aloft briefly taking hold
into Wednesday. The next system could arrive by later Wednesday into
Thursday, and looking at the pattern, this could be the next one to
watch for a potential strong or severe storm threat. Mild conditions
in the 50s and low 60s persist at least through mid to late week
ahead of that next system.

&&

.Aviation (12Z TAF Issuance)
Issued at 650 AM EST Thu Jan 12 2023

Impacts: MVFR/IFR ceilings, showers and storms Thursday morning
(with visibility reductions), wind shift from S/SE to NW

Discussion: An area of low pressure is moving across the Ohio Valley
this morning, with a cold front expected to swing through the region
later this afternoon. So far this morning, guidance has struggled to
capture the exact trends in ceilings, with guidance generally being
too pessimistic. Have adjusted ceilings upward from previous
forecast, with categories likely to bounce around over the next
several hours. Any stronger thunderstorms which pass across
terminals between now and this afternoon will likely reduced
visibilities to MVFR/IFR levels, though confidence in exact timing
of TS remains low.

There is higher confidence in cold frontal passage between 15-20Z,
which will cause winds to veer around from S/SE to NW. Gusts as high
as 25-30 kt are possible during the afternoon and evening hours
Thursday before a gradual easing of winds happens well after sunset.
Toward the end of the current forecast period, some light snow
showers are possible, first at HNB and BWG before working eastward
to SDF and LEX. Confidence in timing/coverage of snow showers
remains low, so have refrained from mention at this time, but
generally expect SNSH to hold off until after 06Z Friday.

Confidence: Low in ceilings, Low in TS, Medium-High in winds/wind
shift, Medium-Low in visibilities (especially in TS).

&&

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

Mesoscale...RAS
Short Term........CSG
Long Term.........BJS
Aviation..........CSG

Hazardous Weather Outlook
National Weather Service Louisville KY
603 AM EST Thu Jan 12 2023

INZ076>079-083-KYZ036-037-041>043-048-049-056-057-067-078-082-131115-
Orange-Washington-Scott-Jefferson-Dubois-Harrison-Fayette-Bourbon-
Nicholas-Jessamine-Clark-Garrard-Madison-Lincoln-Russell-Clinton-
Including the cities of Paoli, Salem, Scottsburg, Madison, Jasper,
Georgetown, Cynthiana, Lexington, Paris, Carlisle, Nicholasville,
Winchester, Lancaster, Richmond, Stanford, Jamestown, and Albany
603 AM EST Thu Jan 12 2023 /503 AM CST Thu Jan 12 2023/

This hazardous weather outlook is for portions of south central
Indiana and Central Kentucky.

.DAY ONE...Today and Tonight.

Multiple rounds of showers and thunderstorms will move across the
area this morning and into the early afternoon hours. A few of the
storms may become strong-to-severe, with damaging wind gusts being
the main severe threat. Isolated large hail is also possible, and one
or two brief tornadoes cannot be ruled out, though the overall threat
is low.

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

No hazardous weather is expected at this time.

.SPOTTER INFORMATION STATEMENT...

Spotter activation may be needed today.

GENERAL STORM MOTION OF THE DAY:

Storms will move from southwest to northeast at 40 to 50 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.

INZ084-089>092-KYZ023>035-038>040-045>047-053>055-061>066-070>077-
081-131115-
Crawford-Perry-Harrison-Floyd-Clark-Hancock-Breckinridge-Meade-Ohio-
Grayson-Hardin-Bullitt-Jefferson-Oldham-Trimble-Henry-Shelby-
Franklin-Spencer-Anderson-Woodford-Nelson-Washington-Mercer-Larue-
Marion-Boyle-Butler-Edmonson-Hart-Green-Taylor-Casey-Logan-Warren-
Simpson-Allen-Barren-Monroe-Metcalfe-Adair-Cumberland-
Including the cities of English, Tell City, Corydon, New Albany,
Jeffersonville, Lewisport, Hawesville, Hardinsburg, Brandenburg,
Hartford, Leitchfield, Elizabethtown, Shepherdsville, Louisville,
La Grange, Bedford, Milton, New Castle, Shelbyville, Frankfort,
Taylorsville, Lawrenceburg, Versailles, Bardstown, Springfield,
Harrodsburg, Hodgenville, Lebanon, Danville, Morgantown,
Brownsville, Horse Cave, Greensburg, Campbellsville, Liberty,
Russellville, Bowling Green, Franklin, Providence, Scottsville,
Glasgow, Tompkinsville, Edmonton, Columbia, and Burkesville
603 AM EST Thu Jan 12 2023 /503 AM CST Thu Jan 12 2023/

...SEVERE THUNDERSTORM WATCH 16 IN EFFECT UNTIL 1 PM EST THIS
AFTERNOON...

This hazardous weather outlook is for portions of south central
Indiana and Central Kentucky.

.DAY ONE...Today and Tonight.

Multiple rounds of showers and thunderstorms will move across the
area this morning and into the early afternoon hours. A few of the
storms may become strong-to-severe, with damaging wind gusts being
the main severe threat. Isolated large hail is also possible, and one
or two brief tornadoes cannot be ruled out, though the overall threat
is low.

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

No hazardous weather is expected at this time.

.SPOTTER INFORMATION STATEMENT...

Spotter activation may be needed today.

GENERAL STORM MOTION OF THE DAY:

Storms will move from southwest to northeast at 40 to 50 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.

CSG/BJS

Special Weather Statement
National Weather Service Louisville KY
927 AM EST Thu Jan 12 2023

KYZ036-037-121500-
Scott KY-Harrison KY-
927 AM EST Thu Jan 12 2023

...Strong thunderstorms will impact portions of northeastern Scott
and northern Harrison Counties through 1000 AM EST...

At 927 AM EST, Doppler radar was tracking strong thunderstorms along
a line extending from 7 miles east of Williamstown to 8 miles north
of Georgetown. Movement was northeast at 65 mph.

HAZARD...Wind gusts up to 50 mph and pea size hail.

SOURCE...Radar indicated.

IMPACT...Gusty winds could knock down tree limbs and blow around
         unsecured objects. Minor damage to outdoor objects is
         possible.

These storms will remain over mainly rural areas of northeastern
Scott and northern Harrison Counties, including the following
locations... Robinson, Colemansville, Breckinridge, Alberta, Renaker,
Mallard Point, Rutland, Berry, Boyd and Claysville.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

If outdoors, consider seeking shelter inside a building.

A Severe Thunderstorm Watch remains in effect until 100 PM EST for
central Kentucky.

&&

LAT...LON 3831 8459 3850 8455 3851 8449 3854 8448
      3853 8445 3857 8441 3858 8421 3858 8420
      3857 8420 3856 8422 3855 8421 3855 8416
      3854 8416 3853 8418 3850 8418 3850 8416
TIME...MOT...LOC 1427Z 243DEG 56KT 3860 8443 3833 8454

MAX HAIL SIZE...0.25 IN
MAX WIND GUST...50 MPH

RJS

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