Special Weather Statement, NWS Louisville, KY

Area Forecast Discussion
National Weather Service Louisville KY
317 PM EDT Tue Jul 6 2021

.Short Term...(This evening through Wednesday)
Issued at 315 PM EDT Tue Jul 6 2021

Isolated to widely scattered convection has fired along a weak W-E
oriented surface trough just south of the I-64 corridor. The
environment is currently characterized by 2000-3000 J/KG of MLCAPE
in the presence of virtually no deep layer shear. So, pulse storm
modes are in play here. Most of the updrafts are struggling under
very weak mid level lapse rates, however a few of the stronger
updrafts that have been 2nd and 3rd generation have overcome the mid
levels to excel. With DCAPE around 1000 J/KG, the gusty wind
potential with any collapsing storm is the main threat. These storms
are presenting a pulse strong to severe threat of isolated
microburst potential. Seeing good velocity signatures off each
microburst, good satellite presentation, and strong outflow
boundaries coming out of collapsing storms all adding confidence in
the gusty wind threat.

Additionally, there is localized heavy rain threat with any slow
moving cell as we saw earlier today in the Lexington Metro. However,
most of the storms will collapse long before they have the potential
to produce enough rain to warrant any advisories/warnings. Will
continue to monitor.

As we move through the afternoon and evening, expect continued
isolated to widely scattered coverage, but coverage will be a bit
more chaotic off the current surface boundary as outflows progress.
Can't rule out any 1 place in our CWA from a short shower or storm,
but think the best coverage will slowly progress northward to along
and north of the I-64 corridor. Still only calling for 20-30%
coverage at any one time.

We should see a relative lull through the overnight with the loss of
daytime heating. If things do clear out enough, patchy fog may be
noted again toward dawn.

Wednesday will bring another round of scattered showers and storms
to the area as PWATs jump across the area thanks to a little help
from the outer moisture from Elsa. In addition, the belt of
westerlies across our north will start to sink into our region ahead
of a shortwave trough that will bring just a little bit more deep
layer flow. Expect things to pop by late morning with coverage
continuing into the afternoon hours. Mid level lapse rates still
won't be impressive so not expecting too many problems, but will
have to watch for localized heavy rain and gusty winds.

&&

.Long Term...(Wednesday night through Tuesday)
Issued at 315 PM EDT Tue Jul 6 2021

At the start of the extended period expect to find a shortwave
trough pushing out of the Upper Midwest and into the Upper Great
Lakes/OH Valley region while a broad upper ridge remains anchored
over the SW CONUS. Across the southeast, Tropical Storm Elsa will
likely be moving through the FL panhandle and into southern GA. At
the surface, a weak cold front will extend southwest across northern
OH/IN and back through the central MS Valley. Scattered showers and
storms may be ongoing across the area Wednesday night as a subtle
wave moves overhead; however, most activity is expected to diminish
with the loss of daytime heating.

As the frontal boundary edges closer Thursday, scattered showers and
storms will continue to be possible throughout the day in a warm and
moist environment characterized by highs generally in the mid to
upper 80s, dewpoints in the upper 60s to lower 70s, and PWATs of 1.6-
1.8 inches. Model soundings indicate moderate instability (SBCAPE ~
1000-2000 J/kg) and shear (Effective Shear ~ 20 kts), while lapse-
rates remain pretty meager around 6 C/km. Any stronger storms may be
capable of producing locally gusty winds and heavy downpours.

Uncertainty increases moving into Friday as model guidance varies on
the placement of the frontal boundary, with the general expectation
being that the cold front will stall out somewhere in the vicinity.
If the cold front is able to push all the way through the area,
would expect mostly dry weather on Friday as northerly flow advects
in cooler and drier air. However, if the boundary stalls out
over/north of the area, a warm and moist airmass in continued SWly
flow could result in afternoon convection once again. Will therefore
maintain mention of slight chance PoPs for Friday.

By this weekend, another shortwave trough will dig southeast through
the northern Plains and into the mid MS Valley where it will remain
rather stationary on Sunday and Monday before lifting to the
northeast by Tuesday. At the surface, an area of low pressure will
develop over the central Plains and gradually progress ENE towards
the mid MS Valley and Upper Midwest by early next week. As we remain
between the low to our northwest and a broad area of high pressure
anchored over the southeast CONUS, deep southwesterly flow will
continue to pump warm and moist air into the region. Scattered
showers and storms will be possible each day through the end of the
period, with diurnally enhanced PoPs in the afternoon and evening
hours. High temperatures will generally remain in the mid to upper
80s each day with overnight lows in the upper 60s to lower 70s.

&&

.Aviation...(18Z TAF Issuance)
Issued at 143 PM EDT Tue Jul 6 2021

Isolated to widely scattered showers and storms have developed along
a weak W-E oriented surface boundary this afternoon and will persist
through the late afternoon and early evening hours before
diminishing. Brief heavy rainfall and gusty winds are the main
threats with these storms, although coverage is too low for the TAF
sites to include any prevailing mention at this time. Will keep VCTS
and plan amendments as necessary. It should be noted that gusty
outflow from storms can disperse well away from t-storm centers, so
erratic and unexpected gusts can't be ruled out at any site. Look
for a quiet overnight with patchy fog potentially an issue again
toward dawn Wednesday. Steady SW winds are expected by late morning
Tuesday with scattered late morning and afternoon storms expected
once again. Prob30s will handle the tomorrow storm chances for now.

&&

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

Short Term...BJS
Long Term...JML
Aviation...BJS

Hazardous Weather Outlook
National Weather Service Louisville KY
331 PM EDT Tue Jul 6 2021

INZ076>079-083-084-089>092-KYZ023>043-045>049-053>057-061>067-
070>078-081-082-071945-
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
331 PM EDT Tue Jul 6 2021 /231 PM CDT Tue Jul 6 2021/

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

.DAY ONE...Tonight.

Scattered thunderstorms are possible through this evening, mainly
along and north of the western Kentucky and Bluegrass Parkways.
Lightning, brief torrential rain, and gusty winds are the main
threats.

.DAYS TWO THROUGH SEVEN...Wednesday through Monday.

Thunderstorms are expected Wednesday and Thursday as a cold front
approaches the region. Some storms could be strong with heavy
rainfall, gusty winds, and marginally severe hail possible. Another
round of storms is possible later into the weekend.

.SPOTTER INFORMATION STATEMENT...

Spotters are encouraged to report any instances of strong gusty winds
or flooding.

&&

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

BJS/JML

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