Severe Thunderstorm Warning 270, NWS Greenville-Spartanburg, SC

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
253 PM EDT Mon Aug 7 2023

.SYNOPSIS...
A cold front crosses our area tonight into early Tuesday. Showers
and thunderstorms will move east and south of our area this evening
as the front will become stationary over central South Carolina.
High pressure builds into the western Carolinas, leading to drier
weather Tuesday into Wednesday. Showers and thunderstorms return on
Thursday.

&&

.NEAR TERM /THROUGH TUESDAY/...
As of 230 PM: A potent shortwave is now centered over the middle
Ohio Valley, with sfc low now in SW Ontario, trailing a cold front
SW'wd to the Ozarks. Robust moisture plume preceding the front
is associated with 5000+ J/kg SBCAPE in much of AL/GA and up to
4000 invof the Southern Appalachians, per mesoanalysis. Short-term
progs depict values continuing to increase thru peak heating in
our CWA; dewpoints have surged into the upper 70s in some parts of
the Upstate. The storms which developed in E TN at midday have now
grown into linear clusters which will move into the NC mountains by
330-400 PM at the latest. This activity appears to be the primary
round affecting western NC.

Shear parameters are generally better toward the north, nearer
the base of the shortwave. While the best forcing will pass by to
our north, strong mid to upper level flow will be present thru the
evening across our CWA. Effective shear will range from 30 to 50 kt
which will aid in the upscale growth; the better helicity parameters
appear to remain north and west of the area, but a gradient thereof
will extend into the CWA. DCAPE has risen above 1200 J/kg across
most of our CWA which will aid in cold pool development. There
is definitely better low-level hodograph curvature toward the
north as one might expect given the above. Shear vectors being
westerly, some potential for circulations along the line(s)
does exist throughout. The tornado threat is best in the north,
and tornado watches have been issued for much of our NC mountains
and I-40 corridor. The strong but unidirectional shear and large
DCAPE make staight-line winds the greatest concern elsewhere,
and a Severe Tstm Watch was just issued to include the rest of
our CWA. Note that there are some additional linear segments in
north AL and vicinity which should track toward GA and the Upstate
later this evening, and in fact some areas could see two rounds
of strong to severe storms.

While CAMs have shown their usual disparities, they all depict
linear MCSs (bow echoes) and swaths of strong wind. The faster
guidance has so far proven more reliable in terms of timing, but
even the slower models show the leading edge of the depicted lines
exiting the CWA by 8-9 PM, so convection should quiet down NLT
that time As the line takes on a more shear-parallel orientation,
can't rule out some localized hydro issues from training along it,
particularly in the urban areas along the I-85 corridor. However,
overall the forward motion of storms should be enough to preclude
a flood threat.

A few showers could linger along the TN/NC border overnight as flow
remains NW to WNW. Some degree of low-level drying is expected via
cold pools or with the arrival of the front itself, but a signal
for dense fog is seen early Tue morning in some of the WNC river
valleys that get heavy rain this evening. Continuing WNW flow is
shown to promote mixing of dewpoints into the lower 60s across
much of the Piedmont tomorrow aftn. Most guidance depicts the
downsloping and/or higher CCLs as keeping any convection highly
isolated at best. We presently advertise near-normal temps with
sub-slight-chance PoPs for most areas Tuesday.

&&

.SHORT TERM /TUESDAY NIGHT THROUGH THURSDAY/...
As of 141 PM EDT Monday: Wednesday's forecast continues to
look quiet, with much of the forecast area ensconced in dry WNW
flow behind a sagging surface boundary to our south, and high
pressure to our north.  Soundings indicate deep mixing to almost
700mb Wednesday afternoon, beneath a stout capping inversion that
should hold anything other than scattered cumulus at bay through
the day.  The cooler Canadian air mass ought to moderate our
temperatures...and indeed temperatures for all but the southernmost
tier of counties in the Upstate will struggle to get out of the
mid-80s, a good 5 degrees below normal for most locations.

Wednesday evening or overnight, a compact shortwave will pivot out
of the Ozarks and into the Southeast CONUS...permitting a return to
deep southwesterly flow and increasing moisture.  A surface front
will develop beneath this feature...to track across the Carolinas
on Thursday.  Upon its arrival, it may encounter another juiced-up
environment, with ensembles in favor of excellent instability (1500-
2000 J/kg per the ECE, as much as 2500 J/kg per some of the more
aggressive GEFS members) and elevated deep shear a good possibility.
There remains the issue of timing/overlap: a few of the operational
models don't quite bring the peak in rainfall/forcing in at the
right time to make use of afternoon instability (peep the 06z GFS
for example)...and there's still a good bit of ensemble spread in
the location of the upper shortwave, whose track will determine
how much shear we get.  Nonetheless, the most favorable forecast
soundings would put us at a risk of severe weather, while even
the most unfavorable soundings would still give us scattered
thunderstorms. So, Thursday looks active at the very least.

&&

.LONG TERM /THURSDAY NIGHT THROUGH SUNDAY/...
As of 159 PM EDT Monday: A pattern shift may be on the way as we get
closer to next weekend. Troughing will persist over the northeast,
but heights will rise subtly beginning Friday as the trough retreats
northward, allowing a subtropical ridge to build over much of the
southern U.S.  The 12z suite of operational guidance hints at
another shortwave making tracks across the Carolinas on
Saturday...which may induce some rainfall...or might just vanish
from the forecast before Saturday (isn't weather forecasting great?)
and leave us with diurnal rain chances more typical of mid-summer in
the Carolinas. By the end of the period, though, it appears that any
additional shortwaves will be shunted north of the Carolinas by the
building subtropical ridge, permitting a return to hot, humid,
seasonable conditions as the Bermuda High nudges westward and
Atlantic moisture creeps into the Carolinas.

&&

.AVIATION /19Z MONDAY THROUGH SATURDAY/...
At KCLT and elsewhere: Main impact this aftn/evening will be from
TSRA forming ahead of a cold front, which prompted TEMPO at all
sites. Storms over E TN are beginning to grow upscale from discrete
cells into a line, and the expectation remains that eventually
bow echoes will threaten all terminals with strong to severe wind
gusts and brief IFR vsby in +RA. A hail or tornado threat does
exist although those are more localized threats. TEMPOs timed per
CAM consensus; the wind threat should subside at all terminals by
00z at the latest, but a few stray lightning strikes trailing the
main line certainly could occur for an hr or two after the wind
threat. Overnight, some upslope driven precip may linger near the TN
border, and some MVFR cigs are possible at KAVL. Drying associated
with cold pools or with synoptic scale front will limit but not
completely inhibit nocturnal fog formation, especially where heavy
rain occurs. For now, confidence is greatest for fog in the WNC
river valleys, hinted at KAVL/KHKY. Low impact weather Tuesday
with low VFR cumulus, and SHRA chances currently too low to mention.

Outlook: Waves moving east along the front will bring daily
chances of scattered diurnal convection Wed through the end of the
week. Daybreak restrictions will be possible each day, especially
across the mountain river valleys.

&&

.GSP WATCHES/WARNINGS/ADVISORIES...
GA...Heat Advisory until 7 PM EDT this evening for GAZ029.
NC...Heat Advisory until 7 PM EDT this evening for NCZ071-072-082.
SC...Heat Advisory until 7 PM EDT this evening for SCZ009-011-014-
     019.

&&

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

Hazardous Weather Outlook
National Weather Service Greenville-Spartanburg SC
247 PM EDT Mon Aug 7 2023

GAZ010-017-018-026-028-NCZ064-065-068>070-507>510-SCZ008-010-012-013-
101>109-081900-
Rabun-Habersham-Stephens-Franklin-Hart-Transylvania-Henderson-
Cleveland-Lincoln-Gaston-Rutherford Mountains-Greater Rutherford-
Polk Mountains-Eastern Polk-Cherokee-Anderson-Laurens-Union SC-
Oconee Mountains-Pickens Mountains-Greenville Mountains-
Greater Oconee-Greater Pickens-Central Greenville-
Southern Greenville-Northern Spartanburg-Southern Spartanburg-
247 PM EDT Mon Aug 7 2023

...SEVERE THUNDERSTORM WATCH 604 IN EFFECT UNTIL 9 PM EDT THIS
EVENING...

This Hazardous Weather Outlook is for northeast Georgia, piedmont
North Carolina, western North Carolina and upstate South Carolina.

.DAY ONE...This afternoon and tonight.

Please listen to NOAA Weather Radio or go to weather.gov on the
Internet for more information about the following hazards.

   Severe Thunderstorm Watch.

Widespread severe thunderstorms are likely this afternoon and evening
ahead of a cold front approaching from the west. Damaging winds are
expected to be the main threat with these storms, but large hail and
a couple of isolated tornadoes will be possible as well. Any
thunderstorm will be capable of producing torrential downpours, gusty
winds, and frequent cloud-to-ground lightning.

.DAYS TWO THROUGH SEVEN...Tuesday through Sunday.

No hazardous weather is expected at this time.

.SPOTTER INFORMATION STATEMENT...

Spotters are requested to forward any reports of large hail,
damaging winds, tornadoes, or flash flooding to our office.

GAZ029-NCZ071-072-082-SCZ009-011-014-019-081900-
Elbert-Mecklenburg-Cabarrus-Union NC-York-Abbeville-Chester-
Greenwood-
247 PM EDT Mon Aug 7 2023

...HEAT ADVISORY IN EFFECT UNTIL 7 PM EDT THIS EVENING...
...SEVERE THUNDERSTORM WATCH 604 IN EFFECT UNTIL 9 PM EDT THIS
EVENING...

This Hazardous Weather Outlook is for northeast Georgia, piedmont
North Carolina and upstate South Carolina.

.DAY ONE...This afternoon and tonight.

Please listen to NOAA Weather Radio or go to weather.gov on the
Internet for more information about the following hazards.

   Heat Advisory.
   Severe Thunderstorm Watch.

Widespread severe thunderstorms are likely this afternoon and evening
ahead of a cold front approaching from the west. Damaging winds are
expected to be the main threat with these storms, but large hail and
a couple of isolated tornadoes will be possible as well. Any
thunderstorm will be capable of producing torrential downpours, gusty
winds, and frequent cloud-to-ground lightning.

.DAYS TWO THROUGH SEVEN...Tuesday through Sunday.

No hazardous weather is expected at this time.

.SPOTTER INFORMATION STATEMENT...

Spotters are requested to forward any reports of large hail,
damaging winds, tornadoes, or flash flooding to our office.

NCZ033-048>053-058-059-062-063-081900-
Avery-Madison-Yancey-Mitchell-Swain-Haywood-Buncombe-Graham-
Northern Jackson-Macon-Southern Jackson-
247 PM EDT Mon Aug 7 2023

...TORNADO WATCH 600 IN EFFECT UNTIL 7 PM EDT THIS EVENING...

This Hazardous Weather Outlook is for western North Carolina.

.DAY ONE...This afternoon and tonight.

Please listen to NOAA Weather Radio or go to weather.gov on the
Internet for more information about the following hazards.

   Tornado Watch.

Widespread severe thunderstorms are likely this afternoon and evening
ahead of a cold front approaching from the west. Damaging winds are
expected to be the main threat with these storms, but large hail and
a couple of isolated tornadoes will be possible as well. Any
thunderstorm will be capable of producing torrential downpours, gusty
winds, and frequent cloud-to-ground lightning.

.DAYS TWO THROUGH SEVEN...Tuesday through Sunday.

No hazardous weather is expected at this time.

.SPOTTER INFORMATION STATEMENT...

Spotters are requested to forward any reports of large hail,
damaging winds, tornadoes, or flash flooding to our office.

NCZ035>037-056-057-501>506-081900-
Alexander-Iredell-Davie-Catawba-Rowan-Caldwell Mountains-
Greater Caldwell-Burke Mountains-Greater Burke-McDowell Mountains-
Eastern McDowell-
247 PM EDT Mon Aug 7 2023

...TORNADO WATCH 603 IN EFFECT UNTIL 9 PM EDT THIS EVENING...

This Hazardous Weather Outlook is for piedmont North Carolina and
western North Carolina.

.DAY ONE...This afternoon and tonight.

Please listen to NOAA Weather Radio or go to weather.gov on the
Internet for more information about the following hazards.

   Tornado Watch.

Widespread severe thunderstorms are likely this afternoon and evening
ahead of a cold front approaching from the west. Damaging winds are
expected to be the main threat with these storms, but large hail and
a couple of isolated tornadoes will be possible as well. Any
thunderstorm will be capable of producing torrential downpours, gusty
winds, and frequent cloud-to-ground lightning.

.DAYS TWO THROUGH SEVEN...Tuesday through Sunday.

No hazardous weather is expected at this time.

.SPOTTER INFORMATION STATEMENT...

Spotters are requested to forward any reports of large hail,
damaging winds, tornadoes, or flash flooding to our office.

MPR

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