Special Weather Statement, NWS Louisville, KY

Area Forecast Discussion
National Weather Service Louisville KY
141 PM EDT Sat Jul 10 2021

...Updated Aviation Discussion...

.Forecast Update...
Issued at 1205 PM EDT Sat Jul 10 2021

Latest sfc analysis shows the wavy frontal boundary sitting across
KY and southern IN. KLVX shows the departing line of showers and
storms that passed through this morning now well off to our east,
but scattered light showers have popped up in the wake across
central KY. Latest HRRR suggest these will dissipate by early
afternoon.

CAMs show an afternoon lull in activity for majority of the CWA, but
the HRRR has been consistent on some renewed activity across the
Cumberland region from 19-20z and into the late afternoon. CAMs also
suggest development of robust convection across MO/IL this afternoon
and dropping south and east into western KY and southern IN by this
evening as a bowing segment/line of storms. Greatest instability
appears to cover the I-65 corridor and pointing west. HREF 12z
ensemble shows mean MUCAPE of 1000-1500 J/kg along I-65, and
increasing to 2000 J/kg across far western KY and southeast MO by
23z this evening. Wind shear appears greatest in the low-mid levels
as 850-700mb winds increase this evening (mostly to our west), with
forecast soundings showing mostly a unidirectional wind profile with
effective shear between 20-30kts. Severe potential appears best for
areas west of I-65, possibly beginning across our southern IN
counties by 22-23z and continuing across our western half of KY
counties into late tonight. Main hazards will be damaging straight
line winds and heavy rainfall. HREF drops instability significantly
by 04z, so severe convection continuing beyond midnight tonight
across southern KY may be hard to come by.

The mix of sun and clouds makes things challenging in regards to
destabilization this afternoon, but latest satellite trends have
cleared to our west much more than initially expected, which would
support greater destabilization. Overall forecast appears in good
shape, but did update near term grids with latest hi-res blend.

&&

.Short Term...(Today and tonight)
Issued at 335 AM EDT Sat Jul 10 2021

...Stormy Weekend, Locally Heavy Rainfall and Severe Weather
Threat...

MCS located across southern IL/eastern MO continues to drop to the
south-southeast. Looking at radar as well as mesoanalysis, the main
threat with this complex is prog to drop south towards the higher
CAPE values along the Mississippi River into southern IL, far
southeastern MO and western KY. The northeastern segment of the line
looks to work along the tight instability gradient and 70 Td
isodrosotherm. Could see it arrive into our far western Indiana
counties by 5am CDT and continue to push east-southeast and along I-
65 by 7-8am CDT (8-9am EDT). Main threat would be gusty winds and
heavy rainfall later this morning.

Stalled boundary across the KY/TN border will start to lift
northward later today into tonight as a sfc low develops IA/MO and
slowly moves eastward into IL by Sunday morning. Warm front will
lift into southern IN this evening as a south-southwesterly flow
advects warmer moist air into the region. Dew point values will get
into the low 70s with PWAT values between 1.7-2.0 inch range. The
axis of highest PWAT values will be across far western KY into
southern IN and along the Ohio River. With these high PWAT values,
and the warm front quasi-stationary along our northern CWA, this
will be the focus of potentially heavy rainfall and training
thunderstorm activity. WPC has a moderate outlook for excess rain
for that area, and HREF ensemble guidance suggest a good probability
of seeing upwards of 2.50-3.00 of rain over the next 24 hours with
potentially higher amounts in areas that see long duration of
training thunderstorms. In coordination with our neighboring WFO's
decided to issue a Flash Flood Watch across most of our northern and
northwestern CWA for from afternoon into Sunday morning.

Along with the threat of heavy rain, there is the potential for
severe weather. The SPC has areas to the east of I-65 in a marginal
risk, while the western half is in a slight risk for severe storms.
CAPE values later today will range between 1500-2000J/kg but shear
values remain marginal closer to 20-25kts. Main threat from any
severe storms looks to be small hail and damaging winds. Could see a
period of just scattered to isolated active as we go into the
afternoon in wake of the passing morning MCS. Hi-res models start to
indicate the development along the warm front later this afternoon
with more scattered active south across central and southern KY.
Then overnight tonight into early Sunday morning more pronounced
area of convection forms as a strong LLJ of 30-40kts begins to nose
in across western KY into southern IN (west of I-65 and along and
north of I-64) enhancing convection.

.Long Term...(Sunday through Friday)
Issued at 300 AM EDT Sat Jul 10 2021

...Showery/Stormy Pattern Ahead...

Sunday - Tuesday...

A deep closed low will be centered over the mid Mississippi River
Valley to end the weekend and start the new work week. Meanwhile, an
upper ridge will be centered off the the mid Atlantic coast during
the same time. The Ohio River Valley will be situated between these
two features, and we'll see a steady plume of deep moisture (gulf
and some help from atlantic moisture as well) advecting poleward
over our area. This is expected to bring waves of showers and storms
over our area with a very high degree of confidence. However, still
not confident in timing individual waves. As mentioned in the
previous discussion, will continue carrying high pops for each
period, but folks should expect breaks in between waves as well.

Given the high PWAT airmass, and south to north training of each
wave, some areas could start to pick up healthy amounts of rainfall
through this time period. Ensemble plumes are suggesting between 2
and 3 inches across much of our area, however localized higher
amounts of 4 inches will be possible with the most likely locations
along and west of I-65 at this time. Think we'll be able to handle a
good majority of the rainfall, but perhaps a few localized problems
will occur at times, especially for spots that see repeated storms.
In addition, gusty winds will be possible with stronger storms each
afternoon/evening, especially if pockets of stronger instability are
able to develop each PM.

Look for pretty consistent high temperatures each day in the low to
mid 80s. Lows will also stay consistent each night in the upper 60s
and low 70s. Overall, these are smaller diurnal ranges than normal
given the expected heavy cloud cover and rounds of precipitation
limiting heating potential.

Tuesday Night - Friday...

The upper low that had been in place over the mid Mississippi River
Valley earlier will be quickly ejecting NE through the Great Lakes
region by Tuesday night, however plenty of deep moisture will
continue to stream over our region on the western periphery of the
upper ridge now centered along the mid Atlantic coast. Overall, this
looks to be a "drier" period of weather than earlier in the week,
however will still need to carry scattered and mainly diurnally
driven pops through around Thursday. By Friday, models generally
agree that better coverage of showers and storms will approach from
the NW along a cold front trailing from an eastern Canada system.

Temperatures look to be a bit warmer during the mid to late week
time frame as more opportunities for heating will occur. As a
result, will go with values more solidly in the mid to upper 80s,
and if convection holds off any one day then values around 90 are
certainly possible. Mild lows in the upper 60s and low 70s will
continue to be the norm.

&&

.Aviation...(18Z TAF Issuance)
Issued at 140 PM EDT Sat Jul 10 2021

Impacts: Showers and storms expected this evening and tonight. Some
storms could be heavy with MVFR/IFR conditions as well as gusty
winds.

Discussion: Visible satellite reveals generally clearing skies
across the region, but sfc obs continue to report some isolated MVFR
cats with BKN clouds around 2500ft. By late this afternoon and into
the early evening, shower and storm chances will increase as a
convective complex exits MO/IL and drops into western KY and
southern IN. HNB and SDF have the best chance to see thunderstorm
impacts this evening, but BWG may see some storms by later tonight.
Thunderstorms are expected to produce heavy rain, frequent
lightning, gusty winds, and lowered visibilities.

Thunderstorm activity will be dissipating around or after 04z, but
lingering showers are possible during the overnight hours has
ceilings look to drop below 2000 ft.

&&

.LMK WATCHES/WARNINGS/ADVISORIES...
IN...Flash Flood Watch through Sunday morning for INZ076>078-083-084-
     089>092.

KY...Flash Flood Watch through Sunday morning for KYZ023>026-030.

&&

Update...CJP
Short Term...BTN
Long Term...BJS
Aviation...CJP

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Special Weather Statement
National Weather Service Louisville KY
149 PM CDT Sat Jul 10 2021

KYZ073-074-101915-
Allen-Barren-
149 PM CDT Sat Jul 10 2021

...A STRONG THUNDERSTORM WILL AFFECT NORTHEASTERN ALLEN AND
SOUTHWESTERN BARREN COUNTIES...

At 148 PM CDT, a strong thunderstorm was located 8 miles north of
Scottsville, moving east at 25 mph.

Winds in excess of 40 mph and half inch hail are possible with this
storm.

Locations impacted include...
Dry Fork, Bristletown, Lucas, Haywood, Austin, Yesse, Gainesville,
Port Oliver Ford, Finney and Peter Creek.

LAT...LON 3684 8620 3692 8619 3692 8618 3694 8616
      3696 8591 3679 8592
TIME...MOT...LOC 1848Z 270DEG 20KT 3687 8614

DM

Special Weather Statement
National Weather Service Louisville KY
209 PM CDT Sat Jul 10 2021

KYZ061-070-101945-
Logan-Butler-
209 PM CDT Sat Jul 10 2021

...A STRONG THUNDERSTORM WILL AFFECT NORTHERN LOGAN AND SOUTHWESTERN
BUTLER COUNTIES...

At 209 PM CDT, a strong thunderstorm was located near Dunmor, moving
east at 25 mph.

Winds in excess of 40 mph and half inch hail are possible with this
storm.

Locations impacted include...
Anderson, Woodbury, South Hill, Huntsville, Dimple, Leetown, Diamond
Springs, Davis Crossroads, Wolf Lick and Harper Crossroads.

LAT...LON 3706 8704 3707 8698 3707 8694 3708 8694
      3709 8690 3710 8690 3711 8689 3713 8690
      3713 8691 3714 8693 3718 8692 3720 8661
      3718 8661 3718 8662 3715 8661 3701 8667
      3699 8667 3702 8705
TIME...MOT...LOC 1909Z 271DEG 35KT 3707 8690

DM

Special Weather Statement
National Weather Service Louisville KY
216 PM CDT Sat Jul 10 2021

KYZ073-074-101945-
Allen-Barren-
216 PM CDT Sat Jul 10 2021

...A STRONG THUNDERSTORM WILL AFFECT NORTHEASTERN ALLEN AND CENTRAL
BARREN COUNTIES...

At 216 PM CDT, a strong thunderstorm was located 10 miles southwest
of Glasgow, moving east at 25 mph.

Wind gusts up to 50 mph and penny size hail are possible with this
storm.

Locations impacted include...
Glasgow, Dry Fork, Eighty Eight, Bristletown, Red Cross,
Pritchardsville, Lucas, Lecta, Haywood and Austin.

LAT...LON 3682 8609 3701 8610 3702 8575 3684 8574
      3684 8578 3682 8581 3679 8586
TIME...MOT...LOC 1916Z 268DEG 24KT 3685 8599

DM

Special Weather Statement
National Weather Service Louisville KY
217 PM CDT Sat Jul 10 2021

KYZ075-081-101945-
Monroe-Cumberland-
217 PM CDT Sat Jul 10 2021

...A STRONG THUNDERSTORM WILL AFFECT NORTHEASTERN MONROE AND WEST
CENTRAL CUMBERLAND COUNTIES...

At 217 PM CDT, a strong thunderstorm was located 7 miles northeast of
Tompkinsville, moving east at 15 mph.

Winds in excess of 40 mph and half inch hail are possible with this
storm.

Locations impacted include...
Leslie, Waterview, Meshack, Persimmon, Ellington, Arat, Cloyds
Landing and Grider.

LAT...LON 3674 8565 3682 8565 3683 8560 3682 8560
      3682 8558 3683 8558 3685 8542 3672 8541
TIME...MOT...LOC 1917Z 266DEG 13KT 3677 8559

DM