Severe Thunderstorm Warning 96, NWS Louisville, KY

Area Forecast Discussion
National Weather Service Louisville KY
340 PM EDT Thu May 19 2022

.Short Term...(This evening through Friday)
Issued at 330 PM EDT Thu May 19 2022

...Severe Storms Expected this Afternoon and Evening...

Synopsis...Strong storms capable of producing severe hail and
damaging winds are already ongoing along the lifting surface
boundary previously located in the Tennessee Valley. Moreover, an
MCV moving later on through south-central Indiana might trigger
another round of severe storms as well as isolated flash flooding
instances. SPC has highlighted an Enhanced risk of severe weather
for northwestern Kentucky and southern Indiana due to the increasing
threat of damaging winds and hail. Also, a Severe Thunderstorm Watch
(#244) is in effect until 8 pm EDT for southern Indiana and most of
the central Kentucky counties west of I-75 to account for the
potential of re-strengthening convection during the late afternoon
and early evening.

This Afternoon and Tonight...A theta-e advection regime has
effectively initialized convection along a line extending NW-SE from
southern Indiana to south-central Kentucky. Initially, the main
severe threat with this line would be damaging winds and large hail,
although a brief tornado cannot be ruled given streamwise vorticity
ingestion due to boundary collision processes. SPC mesoanalysis
reveals effective bulk shear around 30 kts and slightly oblique to
the forcing boundary, which initially favors organized multicellular
storms or supercells. That has been the radar trends during the past
couple of hours. Nonetheless, anvil-level flow and the closed
distance between developing storms indicate that cold pool
interaction will be favored once storms are in the mature phase.
Therefore, storm mergers will be expected during the foreseeable
future. Seems to me that the mean wind is modestly low for upscale
growth at this time.
Persistent moisture advection and clearing behind the current
convective line hint at a quick instability recovery for convective
initiation during the late afternoon and early evening. Enhanced low-
level flow attendant to the MCV circulation and mass response might
be the forcing mechanism for further storm coverage. It is noted
that effective SRH and 0-1 km shear will eventually augment and
overlap with the potential second storm episode. Further
confirmation of a tornado risk is provided by the composites SCP and
STP indexes, both of which increase after 21 Z. Therefore, there is
a conditional risk of tornadoes provided that storms kick off during
the aforementioned time frame. On the other hand, flash flooding
should be closely monitored due to the heavy rain rates already
evidenced on radar and the expected environmental ingredients. The
most vulnerable zones will be the low-lying areas or urban settings
with poor drainage as well as the ones that received rainfall
yesterday and, therefore, the 1-hr (3-hr) FFG is already low.

Friday...Dry air and low-level subsidence will keep precipitation
chances out of the forecast at the start of the weekend. The
combination of solar heating and warm air advection related to deep
southwesterly flow will allow temperatures to soar, probably
breaking some records (see Climate section below). Finally, a
healthy LLJ in combination with steepening near-surface lapse rates
will ensure gusty winds around 30 kts during the afternoon hours.

&&

.Long Term...(Friday night through Thursday)
Issued at 320 PM EDT Thu May 19 2022

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

Upper level flow across NOAM is expected to amplify as western US
trough axis digs through the Rockies.  Downstream ridging across the
eastern US will place the Ohio Valley in broad southwest flow aloft.
Upper trough axis is forecast to push eastward dragging a surface
cold front through the region during the weekend.  Strong to possibly
severe storms will be possible with the cold frontal passage.  A
shot of cooler air will then infiltrate the region late in the
weekend and into early next week.  The upper level pattern then will
amplify once again around mid-week next week with another round of
unsettled weather on tap.

====================================
Meteorological Discussion
Weather Impacts
====================================

Dry weather is expected at the very beginning of the period (Friday
Night) with lows remaining quite mild in the upper 60s to the lower
70s.

On Saturday we'll start off dry once again under southwest flow.  A
surface cold front will be to our northwest and prior to the front
arriving in the area, temperatures will likely warm into the upper
80s and lower 90s.  The surface cold front looks to drop into the
region later Saturday night and into Sunday morning.  Widespread
showers and thunderstorms will accompany the front as it pushes
through.  There is some potential for strong to severe storms, but
in this particular case, much of the stronger/deep layer shear will
reside on the cool side of the frontal boundary and a bit to our
north and west.  Instability may be a bit questionable as well
because if the front passes through overnight, this would be at the
diurnal instability minimum.  Model soundings strongly argue for
mainly elevated convection with this activity.  So for now, will
plan on carrying highest PoPs for Saturday night and into the day on
Sunday.  Sunday looks to be quite wet with widespread showers and
embedded thunderstorms.  Some strong storms may be possible if
pockets of substantial instability develop.  Lows Saturday night
will drop into the low-mid 60s with highs on Sunday averaging in the
lower-mid 70s west of I-65 and highs in the upper 70s to near 80
east of I-65.

Cold front should pull on off to the east late in the day on Sunday
with drier and much cooler conditions coming into the region.  Lows
Sunday night will dip into the lower-mid 50s.  Highs on Monday
should top out in the lower 70s.

The overall upper level pattern will amplify once again starting
around Tuesday as the next upper level wave ejects eastward from the
Plains and into the Midwest and Ohio Valleys. This feature will
bring yet another round of showers and storms to the region for
Tuesday and Wednesday.

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

Overall forecast confidence for the first half of the extended
period is generally medium to high with regards to precipitation
chances and temperatures.  The forecast confidence of severe weather
potential over the weekend remains low at this time.

Forecast confidence for early-mid next week is generally medium with
a low confidence on severe weather risks toward the end of the
forecast period.

&&

.Aviation...(18Z TAF Issuance)
Issued at 140 PM EDT Thu May 19 2022

Weather conditions will deteriorate throughout the afternoon and
early evening as scattered convection develops from west to east.
There is still uncertainty in the model guidance for convection
timing and location which can be explained by the weak nature of the
forcing. Included TEMPO groups in HNB, LEX, and SDF where there is
better agreement on storm probabilities late in the afternoon and
early evening. Non-convective winds will gust this afternoon ahead
of an increasing LLJ; the same that will grant a mention of wind
shear at all terminals overnight. For tomorrow, drier airmass and
clear skies will favor VFR conditions; however, southwesterly flow
will gusts between 25-30 kts.

&&

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

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

Hazardous Weather Outlook
National Weather Service Louisville KY
400 PM EDT Thu May 19 2022

INZ076>079-083-084-089>092-KYZ023>043-045>049-053>057-061>067-
070>078-081-082-202000-
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
400 PM EDT Thu May 19 2022 /300 PM CDT Thu May 19 2022/

...SEVERE THUNDERSTORM WATCH 244 IN EFFECT UNTIL 8 PM EDT /7 PM CDT/
THIS EVENING...

.DAY ONE...This Afternoon and Tonight.

Another round of strong to severe thunderstorms is expected across
the area this afternoon and evening. The main threats will be large
hail, damaging winds, and possibly an isolated tornado. Heavy
rainfall may result in some localized flooding in places.

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

No hazardous weather is expected at this time.

.SPOTTER INFORMATION STATEMENT...

Spotter activation may be needed.

GENERAL STORM MOTION OF THE DAY:

Storms this afternoon and evening will move from the west-southwest
to the east-northeast at 30 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.

MJ

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