Special Weather Statement, NWS Greenville-Spartanburg, SC

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
202 PM EDT Tue Aug 3 2021

.SYNOPSIS...
In situ cold air damming continues into Wednesday leading to well
below normal highs. The wedge should erode late Wednesday into early
Thursday leading to warmer highs Thursday. The chance for diurnal
scattered showers with embedded thunder continues into tomorrow and
Thursday. Highs will continue to increase gradually throughout the
forecast period. Diurnal shower and thunderstorm chances return this
weekend as a trough impacts the area.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 100 PM: Sfc high pressure centered over the NE CONUS at this
hour, maintaining easterly flow and moisture flux and a regime
with a lot of characteristics of in-situ CAD, even if the regime is
missing some of the necessary subsidence aloft. A well defined upper
trough is visible on WV imagery, encompassing the lower Mississippi
Valley. In the exit region of this trough, a leading vort lobe in
conjunction with the RR quad of the upper jet continues to drive
light stratiform precip across central NC and the Pee Dee region
of SC. Some scattered showers are breaking out on radar across the
western half of the CWA, with a few hundred J/kg of SBCAPE already
present, these areas being on the periphery of the weak wedge. An
inverted trough west of the Appalachians appears poised to enhance
this development as a source of sfc convergence. Not sure if this is
a lee trough from easterly flow over the chain or if it is related
to the upper trough. At any rate we retain high chance to likely
PoPs in that area until after the diurnal peak. Not looking like
we're going to break any low-max records despite cool temps; KAVL
was our best hope but appears to have been too warm at midnight.

The 500mb pattern is more or less blocked across the CONUS, with the
trough moving little thru Wednesday due to the monster ridge over
the western Atlantic. Consequently the front lingering near the E
Gulf and S Atlantic coasts will remain nearly stationary. A sfc wave
is set to spin up along the front near Charleston this evening and
track NE toward the Outer Banks overnight. Weak upper convergence
behind departing jet streak, combined with backing low-level flow
inland of the developing low, both suggest a continued decrease
in forcing and slowly declining precip chances thru morning in
general. These could promote strengthening of our wedgelike pattern
and possibly even allow it to become true CAD. Lapse rates remain
pretty good aloft tonight under the trough. The aforementioned
convergence axis near the southern Appalachians does suggest small
PoPs for portions of the western CWA, with some lingering elevated
instability. Elsewhere, mostly cloudy skies are expected to continue
with moisture trapped under inversion and slight shallow upslope
lift continuing.

&&

.SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/...
As of 145 AM EDT Tuesday: An elongated 500mb trough will be
situated over the Ohio Valley at daybreak Wednesday.  This trough
should remain anchored in-place at least through Wednesday evening,
before rapidly lifting east and north on Thursday.  Throughout this
period, the best dynamical forcing will be situated across the
Mid-Atlantic coast, east of our forecast area as a weakening
shortwave phases into the broad trough.  At the surface, the
signal for a cold wedge will persist through Thursday night, as no
large-scale mechanisms will be in place to erode the trapped air.
Although the global models still seem to be dialing back PoPs,
keeping the heavier rainfall well east of our counties, 850mb flow
should start out east-northeasterly on Wednesday, slowly turning
more northerly through Thursday, meaning profiles will be slow to
dry and we can expect significant cloud cover at least through
early Thursday afternoon.  By this point in time, with the mid-
to upper-levels drying and cooling, and the low levels warming in
response to lessening sky cover, the CAD should finally begin to
dissipate from the bottom up.  Thus, PoPs should ramp down beginning
Thursday evening for the entire CWA, being retained the longest
over the mountains, but mostly vanishing to slight/nonexistent by
early Friday morning.

On both Wednesday and Thursday, the best instability appears
confined to the mountains, as they'll receive better insolation and
the rest of the area should be fairly well-capped by the CAD wedge.
So, both afternoons, spotty ridgetop convection is possible,
but without any major concern for SVR or heavy rain potential.
Temps should remain below normal both days, likely trending upward
a bit on Thursday as cloud cover breaks up.

&&

.LONG TERM /FRIDAY THROUGH TUESDAY/...
As of 215 AM EDT Tuesday: From Friday through Saturday night,
a shortwave will drop out of the Midwest and bring ripples of
upper forcing across the region Friday and Saturday afternoon.
With surface flow turning southerly by Friday afternoon, profiles
should moisten significantly, making for modest instability on
Friday evening and potentially more robust CAPE on Saturday.

Sunday and beyond, the subtropical ridge will reinforce a developing
Bermuda high, prompting southeasterly surface flow, while aloft,
a 500mb ridge will suppress widespread cloud cover and precip.
Thus, by the end of the weekend and beyond, we'll return to the
usual late-summer diurnal convective mode.  Near-normal temps
on Friday and Saturday will creep at least a degree or two above
normal on Sunday, as improving insolation and WAA off the Atlantic
prompt warming.

&&

.AVIATION /18Z TUESDAY THROUGH SUNDAY/...
At KCLT and elsewhere: Most of the area remains under MVFR stratocu
cigs associated with a CAD-like easterly flow regime, driven by high
pressure over the NE CONUS. A boundary is evident from satellite
imagery west of KCLT, possibly dividing stable air associated
with the "parent high" from more unstable air to the west. All
sites except KCLT are on the unstable side and will be subject
to scattered SHRA this afternoon. The main impact would be brief
vsby restrictions to MVFR or even IFR. A stray TS is not out of
the question. Most guidance depicts gradual deepening of the mixed
layer such that most sites should be low VFR by late afternoon. The
overall pattern changes little tonight; increasing subsidence over
the high will maintain the CAD-like regime and may even enhance
it. Thus, whatever cloud cover is present at sunset looks likely
to persist into morning. Lowering of VFR to MVFR is even progged
for the lower Piedmont including KCLT. Mountain valley fog also
looks likely, so take KAVL to IFR near daybreak. Diurnally driven
SHRA are expected again Wednesday mainly over the higher terrain;
only KAVL gets a mention as VCSH.

Outlook: The usual chance of diurnal convection returns to the
forecast area from Wednesday thru Friday. Fog/low stratus will be
possible each morning, particularly for the mountain valleys and
areas primed by rainfall from the previous evening.

Confidence Table...

            18-24Z        00-06Z        06-12Z        12-18Z
KCLT       High  93%     High  97%     High  84%     High  84%
KGSP       High  88%     High  99%     High  95%     High  96%
KAVL       High  81%     Med   70%     Med   76%     High  87%
KHKY       High  90%     High 100%     High  98%     High  97%
KGMU       High  88%     High 100%     High  89%     High  94%
KAND       High  83%     High  92%     Med   75%     Med   79%

The percentage reflects the number of guidance members agreeing
with the scheduled TAF issuance flight rule category. Complete hourly
experimental aviation forecast consistency tables are available at
the following link:

www.weather.gov/gsp/aviation

&&

.CLIMATE...
RECORDS FOR 08-03

               MAX TEMPERATURE         MIN TEMPERATURE
  STATION      HIGH        LOW         HIGH        LOW
  -------  ----------  ----------  ----------  ----------
   KAVL      94 1957     71 1909     72 2010     50 1998
   KCLT      98 2011     68 1909     77 1881     60 1998
                1888                                1985
   KGSP     100 2011     71 1909     75 2010     58 1985

&&

.GSP WATCHES/WARNINGS/ADVISORIES...
GA...None.
NC...None.
SC...None.

&&

SYNOPSIS...AP
NEAR TERM...Wimberley
SHORT TERM...MPR
LONG TERM...MPR
AVIATION...Wimberley
CLIMATE...Wimberley

Hazardous Weather Outlook
National Weather Service Greenville-Spartanburg SC
454 AM EDT Tue Aug 3 2021

GAZ010-017-018-026-028-029-NCZ033-035>037-048>053-056>059-062>065-
068>072-082-501>510-SCZ001>014-019-040900-
Rabun-Habersham-Stephens-Franklin-Hart-Elbert-Avery-Alexander-
Iredell-Davie-Madison-Yancey-Mitchell-Swain-Haywood-Buncombe-Catawba-
Rowan-Graham-Northern Jackson-Macon-Southern Jackson-Transylvania-
Henderson-Cleveland-Lincoln-Gaston-Mecklenburg-Cabarrus-Union NC-
Caldwell Mountains-Greater Caldwell-Burke Mountains-Greater Burke-
McDowell Mountains-Eastern McDowell-Rutherford Mountains-
Greater Rutherford-Polk Mountains-Eastern Polk-Oconee Mountains-
Pickens Mountains-Greenville Mountains-Greater Oconee-
Greater Pickens-Greater Greenville-Spartanburg-Cherokee-York-
Anderson-Abbeville-Laurens-Union SC-Chester-Greenwood-
454 AM EDT Tue Aug 3 2021

This Hazardous Weather Outlook is for northeast Georgia, Piedmont
North Carolina, western North Carolina and Upstate South Carolina.

.DAY ONE...Today and tonight.

There is a chance of isolated showers and a few thunderstorms this
afternoon, especially across the NC foothills and mountains. These
storms will be capable of producing brief heavy rain and occasional
cloud- to- ground lightning.

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

Hazardous weather is not expected at this time.

.SPOTTER INFORMATION STATEMENT...

None.

MPR

Special Weather Statement
National Weather Service Greenville-Spartanburg SC
218 PM EDT Tue Aug 3 2021

NCZ059-031900-
Northern Jackson NC-
218 PM EDT Tue Aug 3 2021

...HEAVY RAIN SHOWERS WILL IMPACT NORTHWESTERN JACKSON COUNTY UNTIL
300 PM EDT...

At 216 PM EDT, Doppler radar was tracking a series of a heavy rain
showers 5 miles north of Sylva. These showers were nearly stationary
and redeveloping in the same location.

Locations to be impacted include... The Blue Ridge Parkway from the
Smoky Mountains To Balsam Gap and Cherokee. Rapid stream rises are
expected along Soco Creek.

Very heavy rainfall rates up to one inch per hour will be possible
in these areas. Deep ponding of water will develop in low-lying and
poor drainage areas.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Torrential rainfall may flood areas with poor drainage, such as
ditches and underpasses. Avoid these areas and do not cross flooded
roads. Water levels of small streams may also rise rapidly. Seek
higher ground if threatened by flood waters.

&&

LAT...LON 3547 8332 3550 8328 3552 8324 3552 8322
      3551 8321 3552 8320 3551 8316 3549 8315
      3549 8314 3546 8313 3542 8318 3539 8327
      3547 8333
TIME...MOT...LOC 1816Z 242DEG 0KT 3545 8323

HG