Severe Thunderstorm Warning 145, NWS Greenville-Spartanburg, SC

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
240 PM EDT Sun Jul 2 2023

.SYNOPSIS...
Hot and humid conditions are expected to continue at least through
the first half of the week. Also expect chances for pop-up
thunderstorms in the afternoons. Temperatures are expected to remain
a few degrees above normal, with mostly light and variable winds. A
cold front is expected to drift south across our region by next
weekend which should cool temperatures a few degrees.

&&

.NEAR TERM /THROUGH MONDAY/...
As of 230 PM Sunday:  The upper synoptic pattern is shifting toward
a more typical summer pattern with broad and weakening flow aloft.
Today, an upper low across the upper Midwest and accompanying broad
trough will dip through the southeast, allowing for a wide swath of
DPVA along the trough axis. Along with continued low level WAA and
abundant sunshine, the atmosphere is destabilizing once again for
another round of convection this afternoon and evening. As the sun
continues to rapidly warm the area, instability increases with 2500-
3000 J/kg of SBCAPE and steep low and mid-level lapse rates nearing
8.3 and 7.0 C/km respectively. One limiting factor is the upper
shear as the sfc-6km shear is around 20kts. This may inhibit the
overall strength of the updrafts, but strong to severe thunderstorms
are still expected. CAM guidance once again has been disagreeing
with the initialization of convection across the region this
afternoon. SPC does have the northwestern half of the CWA in a
Slight risk for today, with the main hazards being damaging winds
and hail. Given the environmental parameters mentioned, confidence
is increasing that storms will develop this afternoon into the
evening hours. Aside from thunderstorms, another concern for a good
chunk of the CWA are the daytime high temperatures and associated
heat indices. With clearer skies this morning and only a few
scattered high clouds, temps are quickly climbing. Given the holiday
weekend and the higher chance for more folks to be outside, we went
ahead and issued a Heat Advisory in effect from noon through 8PM
tonight for heat index values around 105+. This is for the SC and NC
Piedmont. Overnight, temps should come back down and there is a
chance for another round of thunderstorms. CAM guidance hint at a
possible line of storms coming through the area in the wee morning
hours, well ahead of a cold front off the NW. Patchy fog could also
form in the mountain areas, but will highly depend on how much
precip falls from afternoon/evening storms. By Monday morning, any
fog that developed overnight should quickly dissipate. Partly cloudy
skies to start the week and another hot and muggy day. Highs are
expected to be in the low to mid 90s again, with heat indices likely
reaching 105+ in some of the southern areas. A Heat Advisory will be
in effect again for tomorrow. Another round of convection likely
Monday afternoon and evening. SPC has the southern tier of the CWA
in a slight risk for the area with the main threats being damaging
wind and hail.

&&

.SHORT TERM /MONDAY NIGHT THROUGH WEDNESDAY/...
As of 230 PM Sunday: Ill-defined cold front still appears to
settle through most of the CWA by the morning of the 4th of
July. CAMs generally depict convection waning diurnally along
the front, although some activity may be maintained, or respawn,
after 00z especially where lift is enhanced by the shortwave
skirting by to our north. That looks more likely to occur in
central NC/VA to our northeast, but can't be completely ruled
out for portions of our CWA. Furthermore, some guidance depicts
the trailing, weaker wave in the Mid-South enhancing convergence
along the boundary in the predawn hours. This could result in
showers/storms creeping back into the western CWA at that time.
For the daytime hours, slightly drier low- to mid-level air will
arrive behind the front, partly the result of downsloping
westerly winds. This should allow dewpoints to mix out a bit
more Tuesday compared to Monday, and max temps a degree or two
cooler. Convectively, should be a seasonable pulse-storm
environment with weak shear and high sfc-midlevel theta-e
lapses, posing at least isolated damaging wind risk if storms
develop. A point of contention among guidance is whether
dewpoints mix out enough to preclude convective initiation; the
NAMs for one depict little to no coverage thru 00z Wed, but
global models depict QPF. Given the nearby boundary and that the
shortwave will creep in from the west overnight, not surprising
that some QPF lingers overnight in those models, and the NAM
follows suit early Wed morning.

The shortwave is expected to center over the southern Appalachians by
Wednesday afternoon; the boundary will remain ill-defined at that
time and its position/orientation may not change meaningfully.
However, PWATs tick upward on some guidance, and sfc dewpoints may
remain higher thru the day on account of somewhat more southerly
low-level winds (albeit weak). As a result we end up with somewhat
higher PoPs than Tuesday, with pulsey storms again the norm. Primary
threat may shift slightly more in favor of heavy rain or localized
flash flooding compared to microburst winds, but either way still
pretty typical for this time of year.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH SATURDAY/...
As of 130 PM Sunday: No appreciable change to the expectations
Thursday into next weekend. The weak front washes out into a very
weak convergence zone only evident as a swath of enhanced moisture
across the Southeast. Weakly cyclonic flow will continue aloft as
upper trough traverses the northern tier of the CONUS. The result is
that global models depict greater than typical coverage of mainly
diurnal convection each day, and accordingly PoPs will be above climo
throughout the CWA. Best overall chances still appear Friday into
Friday night, as the trough brings a seasonably weak cold front to
the Appalachians. Seasonable heat and humidity, with heat index
peaking near 100 in the warmest lower Piedmont locations each
afternoon.

&&

.AVIATION /19Z SUNDAY THROUGH FRIDAY/...
At KCLT and elsewhere: All terminals prevailing VFR through the end
of the TAF period. A few rounds of TS, the first being this
afternoon and into the evening hours. Likely time for development is
around 21/22z, therefore TEMPOs for TSRA at all sites starting at
22z, with KCLT at 23z. Depending on how much rain falls across the
mountains will determine the strength of fog/low stratus development
across the mountains. KAVL could see a few hours with lower VSBY and
improve before sunrise. A second round of convection could develop
overnight across the mountains and into the Piedmont, so PROB30 for
TSRA at all sites except KCLT. Tomorrow, skies looks to be generally
scattered with high and a few mid level clouds throughout the day.
For KCLT, PROB30 for another round of afternoon convection. Winds
will remain S/SW and light with an occasional 15kt gust possible
through the end of the TAF period.

Outlook: A weak cold front will move into the region early this week
and maintain a chance of showers and thunderstorms during the
afternoon and evening periods.

&&

.GSP WATCHES/WARNINGS/ADVISORIES...
GA...Heat Advisory until 8 PM EDT this evening for GAZ018-026-028-
     029.
     Heat Advisory from 10 AM to 8 PM EDT Monday for GAZ029.
NC...Heat Advisory until 8 PM EDT this evening for NCZ068>072-082-
     507>510.
     Heat Advisory from 10 AM to 8 PM EDT Monday for NCZ071-072-082.
SC...Heat Advisory until 8 PM EDT this evening for SCZ008>014-019-
     101>109.
     Heat Advisory from 10 AM to 8 PM EDT Monday for SCZ009-011-014-
     019.

&&

SYNOPSIS...DEO
NEAR TERM...CP
SHORT TERM...Wimberley
LONG TERM...Wimberley
AVIATION...CP

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Special Weather Statement
National Weather Service Greenville-Spartanburg SC
447 PM EDT Sun Jul 2 2023

NCZ048-022115-
Madison NC-
447 PM EDT Sun Jul 2 2023

...A strong thunderstorm will impact portions of central Madison
County through 515 PM EDT...

At 447 PM EDT, Doppler radar was tracking a strong thunderstorm 7
miles west of Marshall, or 5 miles south of Hot Springs, moving east
at 15 mph.

HAZARD...Wind gusts up to 40 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.

Locations impacted include...
Marshall, Hot Springs, Spring Creek and Walnut.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

If outdoors, consider seeking shelter inside a building.

Frequent cloud to ground lightning is occurring with this storm.
Lightning can strike 10 miles away from a thunderstorm. Seek a safe
shelter inside a building or vehicle.

&&

LAT...LON 3595 8257 3577 8260 3573 8268 3575 8289
      3589 8290
TIME...MOT...LOC 2047Z 266DEG 13KT 3581 8281

MAX HAIL SIZE...0.25 IN
MAX WIND GUST...40 MPH

CAC

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