Severe Thunderstorm Warning 239, NWS Louisville, KY

Area Forecast Discussion
National Weather Service Louisville KY
337 PM EDT Sat Aug 20 2022

.Short Term...(This evening through Sunday)
Issued at 335 PM EDT Sat Aug 20 2022

Synopsis...Meandering mid-level low over the Midwest will start
moving through the Great Lakes and into the Northeast US during the
next 48 hours and open up as a shortwave trough while several vort
max impulses round the base of the trough and eject ahead of it. At
the surface level, low pressure system will follow suit and
eventually intensify with attendant weak cold front approaching the
forecast area during Sunday night. Although the mesoscale frontal
forcing will be frail, the above scenario will support persistent
mid-to-upper level synoptic forcing through upper jet dynamics,
sufficient effective bulk shear thanks to a +70 kts 250-mb jet core,
and moisture rich southwesterly flow.

Rest of Saturday afternoon...As previously stated in earlier
updates, convection has started to multiply around the forecast area
with the strongest storms at this hour located in the Bowling Green
vicinity. Earlier uninterrupted insolation and high dewpoints have
yield instability values well above 2,500 J/kg and steepening low-
level lapse rates which in conjugation with dry-air in the 700-500
mb layer reinforce the marginal risk of locally severe wind gusts.
On top of that, the expected uptick in the mid-level environmental
wind has caused effective bulk shear values between 25-35 knots this
afternoon; therefore, the preferred storm mode at initiation will be
cellular with some transient supercell structures provided the low-
level SR wind is favorable for further maintenance. Then, a more
linear mode is favored given the inverted V feature shown on the
forecast soundings that advocate for cold pool prevalence.
Marginally severe hail, frequent lightning, and heavy rainfall are
other hazards associated with today's storms. Regarding location of
highest impacts, SPC has a marginal risk of severe weather roughly
along and north of I-64, but the HRRR SSCRAM model has been
persistent on exhibiting the best severe probabilities along and
east of I-65, in line with current radar imagery.

Saturday Night...Anticipate a downward convective trend after sunset
with most of the storms pushing far away to the east. However, there
is a low chance that  a convective outflow ahead of the approaching
cold front could still impact southern Indiana during the first half
of the night. There is some CAM guidance support towards this
output with SCP values between 3-6. Considering a near-surface
stable layer and decreased instability, it will be difficult for any
elevated severe gust to reach the surface. So, small hail and strong
wind gusts are the main impacts for tonight.

Sunday...Best storm intensity and coverage will probably be in the
morning and early afternoon as the left exit region of the upper jet
spreads through central Kentucky, well ahead of the weak cold front.
There will be an instability gradient due to the cloud coverage in
place to the north which will limit diabatic heating. Low-level
winds will slightly increase and turn to the south due to the
passing surface low to the north. This, in turn, will support a low-
end tornado threat during the afternoon when the SCP is also
maximized. Bulk shear values will be once again ranging between 25
to 35 knots, so a mix of multicells and hybrid supercells is
expected

&&

.Long Term...(Sunday night through Saturday)
Issued at 315 PM EDT Sat Aug 20 2022

====================================
Synoptic Overview
====================================

The period will start off with an upper level trough axis crossing
the upper Ohio Valley.  This wave, progressive in nature, will
translate eastward into New England by late Monday.  Behind the
departing wave, a long wave trough axis will be maintained across
the eastern US with a persistent ridge axis out across the west. The
Ohio Valley will remain in a northwesterly flow aloft with mainly
dry conditions from Tuesday through Thursday night.  Some increase
in moisture may occur by late week with the possibility of at least
some isolated-scattered diurnally driven convection by Friday-
Saturday.

====================================
Meteorological Discussion
====================================

Sunday night thorugh Monday night:

Showers and thunderstorms should be in progress at the start of the
period (Sunday night) and will continue into the day on Monday as
the upper trough axis moves east and a cold front finally push
through the region.  Best chances of precipitation on Monday will be
mainly across the eastern CWA.  Lows Sunday night will be in the mid-
upper 60s with highs on Monday warming into the low-mid 80s.  Dry
conditions should be in place by Monday night with lows cooling into
the lower 60s.

Tuesday through Saturday:

With the trough well to our east, a lagging long wave trough axis
will remain in place through much of next week across the eastern US
while the western US remains under ridging.  We will have a
relatively quiet period of northwest flow across the region.  While
the global models keep things generally quiet, it is possible that
some smaller scale perturbations may drop through during the period
and could produce isolated showers/storms.  Given the predictive
scale at days 4-5 here, overall confidence is fairly low at this
point.  Temperatures will remain seasonal for late August with highs
in the mid-upper 80s, though some of the urban centers may be a tad
warmer.  Overnight lows will generally be in the mid-upper 60s.  By
Friday-Saturday daytime highs will generally be in the upper 80s to
near 90 in spots.  Some return flow moisture may start to creep
northward in the Friday-Saturday period.  This would at least set
the stage for some isolated diurnally driven convection in the
afternoons.

====================================
Weather Hazards/Risks
====================================

Showers and thunderstorms Sunday night and Monday may produce heavy
rainfall, gusty winds and lightning.  The progressive nature of the
storms should keep residence times of storms over any location to a
minimum.  However, some isolated hydrologic issues in low-lying and
poor drainage areas is possible.

====================================
Forecast Confidence
====================================

Overall forecast confidence with this period with respect to
precipitation is medium.  Confidence on temperatures is medium-high.

&&

.Aviation...(18Z TAF Issuance)
Issued at 130 PM EDT Sat Aug 20 2022

Impacts/Confidence:
- Low confidence on timing and location of storms coverage
- Low confidence on MVFR CIG tomorrow morning at HNB, SDF, and BWG
- Medium confidence on MVFR CIG tomorrow morning at LEX.

Discussion...Anticipate several waves of showers to swing through
souther Indiana and northern Kentucky during this TAF cycle.
Overall, there is still uncertainty on location and timing of
impactful weather due to the lack of robust forcing with the current
scenario. As a result, used a combination of VCSH/VCTS and PROB30
groups to reflect the best solution possible at the moment.
Additionally, guidance is insisting on MVFR ceilings after sunrise
tomorrow with even Fuel Alternate category at some sites. So far,
only indicated MVFR CIG at LEX while other terminals are barely VFR
pending better agreement on coming forecast updates.

&&

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

Short Term...ALL
Long Term...MJ
Aviation...ALL

Hazardous Weather Outlook
National Weather Service Louisville KY
347 PM EDT Sat Aug 20 2022

INZ076>079-083-084-089>092-KYZ023>043-045>049-053>057-061>067-
070>078-081-082-212000-
Orange-Washington-Scott-Jefferson-Dubois-Crawford-Perry-Harrison-
Floyd-Clark-Hancock-Breckinridge-Meade-Ohio-Grayson-Hardin-Bullitt-
Oldham-Trimble-Henry-Shelby-Franklin-Spencer-Anderson-Woodford-
Fayette-Bourbon-Nicholas-Nelson-Mercer-Jessamine-Larue-Marion-Boyle-
Garrard-Madison-Butler-Edmonson-Hart-Green-Taylor-Casey-Lincoln-
Logan-Warren-Simpson-Allen-Barren-Monroe-Metcalfe-Adair-Russell-
Cumberland-Clinton-
Including the cities of Paoli, Salem, Scottsburg, Madison, Jasper,
English, Tell City, Corydon, New Albany, Jeffersonville, Lewisport,
Hawesville, Hardinsburg, Brandenburg, Hartford, Leitchfield,
Elizabethtown, Shepherdsville, Louisville, La Grange, Bedford,
Milton, New Castle, Shelbyville, Frankfort, Georgetown, Cynthiana,
Taylorsville, Lawrenceburg, Versailles, Lexington, Paris, Carlisle,
Bardstown, Springfield, Harrodsburg, Nicholasville, Winchester,
Hodgenville, Lebanon, Danville, Lancaster, Richmond, Morgantown,
Brownsville, Horse Cave, Greensburg, Campbellsville, Liberty,
Stanford, Russellville, Bowling Green, Franklin, Providence,
Scottsville, Glasgow, Tompkinsville, Edmonton, Columbia, Jamestown,
Burkesville, and Albany
347 PM EDT Sat Aug 20 2022 /247 PM CDT Sat Aug 20 2022/

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

.DAY ONE...Tonight.

Scattered strong to severe storms will be possible Saturday
afternoon and evening. Main threats are locally severe wind gusts,
small hail, and frequent lightning. Then, quiet weather conditions
are expected after midnight with small chance of isolated storms in
southern Indiana.

.DAYS TWO THROUGH SEVEN...Sunday through Friday.

Numerous showers and thunderstorms are expected Sunday ahead of a
cold front. Some of the storms could become strong with gusty winds,
lightning, and hail as the main threats.

.SPOTTER INFORMATION STATEMENT...

Spotter activation may be needed Sunday.

GENERAL STORM MOTION OF THE DAY:

Showers and storms will move from the southwest to the northeast at
15 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.

ALL/MJ

Special Weather Statement
National Weather Service Louisville KY
514 PM EDT Sat Aug 20 2022

INZ079-202130-
Jefferson IN-
514 PM EDT Sat Aug 20 2022

...A strong thunderstorm will impact portions of north central
Jefferson County through 530 PM EDT...

At 514 PM EDT, Doppler radar was tracking a strong thunderstorm 10
miles northwest of Madison, moving northeast at 20 mph.

HAZARD...Wind gusts of 50 to 55 mph.

SOURCE...Radar indicated.

IMPACT...Gusty winds could knock down tree limbs and blow around
         unsecured objects.

This storm will remain over mainly rural areas of north central
Jefferson County, including the following locations... Middlefork,
Dupont, Bryantsburg, Five Points and Barbersville.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

If outdoors, consider seeking shelter inside a building.

This storm may intensify, so be certain to monitor local radio
stations and available television stations for additional information
and possible warnings from the National Weather Service.

&&

LAT...LON 3881 8549 3888 8556 3888 8554 3891 8554
      3891 8527
TIME...MOT...LOC 2114Z 236DEG 16KT 3887 8548

MAX HAIL SIZE...0.00 IN
MAX WIND GUST...55 MPH

EBW

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