Special Weather Statement, NWS Greenville-Spartanburg, SC

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
233 PM EDT Sun Oct 3 2021

.SYNOPSIS...
A cold front will approach the area today and settle over
the region Monday into Tuesday, bringing a prolonged period of
widespread shower activity.  High pressure centered over New England
will extend down into our region Wednesday through Friday as an
upper-level low persists to our west and a cold wedge potentially
builds into the area late-week. This pattern will keep shower
chances in place at least into next Saturday, when the upper-low
finally starts to weaken and conditions dry out again.

&&

.NEAR TERM /THROUGH MONDAY/...
As of 215 PM: Deep plume of moisture, short wave, and upper
divergence are moving into the area from the west. As a result,
widespread showers are moving across the mountains. Expect the
showers to only make slow progress to the east through the evening
and overnight as the showers themselves move northeast across the
area. Weak instability and shear with moderate forcing means only
isolated thunderstorms expected with no significant chance of severe
storms. Do expect some training of cells given the slow eastward
movement of the overall system, but there aren't any significant
heavy rainfall signals. Therefore, the heavy rainfall threat looks
limited with only a very low threat of flooding. Lows up to 10
degrees above normal.

Deep moisture and short wave forcing remain over the area Monday,
but upper divergence weakens. Expect showers to continue across the
area but have gone with likely PoP for now. Instability and shear
remain weak with moderate forcing. Therefore, thunder chances remain
limited with no significant chance fo severe storms. The potential
for excessive rainfall also remains quite low. Highs will be near
normal west and a couple of degrees above normal east.

&&

.SHORT TERM /MONDAY NIGHT THROUGH WEDNESDAY/...
As of 130 PM EDT Sunday: Monday night, a 500mb cutoff low will have
formed, positioned over the Ozarks, with broad zonal flow over the
Midwest gradually transitioning to ridging as higher heights push
in from the Great Plains.  A subtropical ridge will be positioned
over the western Atlantic, and as northern-stream ridging builds
in across the northeast CONUS on Tuesday and the first part of
Wednesday, the subtropical ridge will actually retrograde slightly
westward, inducing height rises over the Carolinas.  Despite this,
as the aformentioned upper low stalls over the the AK/MO region,
successive lobes of DPVA will rotate around it and cross over
the western part of the Carolinas and providing significant
synoptic forcing.  At the surface, southeasterly onshore flow
driven by the Bermuda high will remain weak but steady, allowing
moisture to filter into the forecast area.  By Tuesday evening,
PWATs should creep up to between 1.5" and 1.8".  Simultaneously, a
region of upper-level divergence will align itself with the midlevel
forcing described above, creating an even-more-favorable environment
for synoptic uplift.  Convective forcing will be otherwise weak;
despite a cold frontal boundary stalling over the eastern tier
of the forecast area, frontogenetical forcing will wane compared
to Monday as the boundary becomes overall increasingly diffuse.
Models are generally pushing below 1000 J/kg of SBCAPE, and this
only really across the eastern Piedmont and southern Upstate,
so while some embedded convection cannot be entirely ruled out,
rainfall should be dominated by widespread stratiform showers.

All that to say, any flood threat should be limited.  Despite
elevated PWATs, weak steering flow, and model QPFs pushing 3" in the
mountains, the fairly thin warm cloud layer and lack of turbulence
updrafts should hinder efficient rainfall from developing, making
the flash flood threat overnight localized.

By now, ridging over the Great Lakes should help spin up broad
high pressure in New England and Quebec.  Onshore moisture flux
diminishes somewhat on Wednesday in response to developing
easterly flow from this surface high.  Model guidance has
developed an ever-more-prominent signal for a hybrid CAD event by
mid- to late-week, with an inverted ridge clearly evident east
of the Appalachians; the GFS and CMC produce the most "wedgy"
result, while the ECMWF is less enthused, and more light-handed
in bringing the wedge south into the Carolinas.  So, in all but
the EC's solution, instability is severerly limited across the
forecast area Wednesday afternoon, and any convection that manages
to develop should be well-capped.

Generally speaking, moist and cloudy conditions will limit
the diurnal range leading to below-normal afternoon highs and
above-normal overnight lows.  With a cold wedge potentially building
in, will need to consider just where the wedge boundary sets up -
as naturally, there will be a wide difference in max/min temps on
either side of this boundary.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/...
As of 200 PM EDT Sunday: With a deteriorating trough still situated
over eastern AK/MO and only beginning to meander northward,
upper flow will remain southwesterly through Thursday and Friday.
Profiles indicate veering through the 1000-500mb layer, which would
suggest WAA.  This should further enhance the cold wedge in situ,
by by driving increased precip changes and by effectively further
stabilizing the low levels.  Most guidance depicts the southern
Blue Ridge receiving 3-4" of rain through Friday, with terrain
inducing locally higher totals as usual.  Still, with those totals
spread across multiple days and with precip efficiency remaining
low compared to many of the convective showers we've seen in recent
weeks, flood risk may remain comparatively small.

Friday night, as the stagnant trough finally begins to lift out,
heights should start to rise again, and profiles begin to dry out
as air filters in from the interior of the CONUS.  Certainty is not
great at this point - we will have to content with both a lifting
trough whose behavior is not yet handled well by the global models,
and the notoriously-unpredictable CAD erosion.  At any rate, PoPs
should generally ramp down through Sunday, as moisture becomes
lacking and synoptic conditions become increasingly unfavorable
for the rainfall needed to maintain the wedge.  Failing any other
erosion mechanism, a weak cold frontal passage late Saturday into
Sunday, associated with the lifting trough, should help finally
clear out what might remain of the wedge.

Generally low convective risk through the extended period.  Assuming
the wedge materializes and remains in place, it should severely
limit instability and provide an effective cap for initiation.
Temperatures will stay generally below-normal for as long as the
wedge is in place.

&&

.AVIATION /19Z SUNDAY THROUGH FRIDAY/...
At KCLT and elsewhere: Showers will move over/near all but KCLT this
afternoon. May be an isolated TSRA as well. MVFR possible as cells
move over the air fields. SW wind expected through the afternoon.
cigs fall from low VFR to MVFR overnight with continued showers.
MVFR vsby likely with IFR vsby possible. Light SW wind overnight.
MVFR cigs Monday should lift to low VFR by afternoon. Vsby becomes
VFR as well. Showers and isolated to scattered thunderstorms
expected with brief restrictions possible as cells move across the
airfields. SW wind expected.

Outlook: Increasing moisture is expected to result in more frequent
flight restrictions and elevated precip chances throughout the week.

&&

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

&&

SYNOPSIS...MPR
NEAR TERM...RWH
SHORT TERM...MPR
LONG TERM...MPR
AVIATION...RWH

Hazardous Weather Outlook
National Weather Service Greenville-Spartanburg SC
426 AM EDT Sun Oct 3 2021

GAZ010-017-018-026-028-029-NCZ033-035>037-048>053-056>059-062>065-
068>072-082-501>510-SCZ001>014-019-041100-
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-
426 AM EDT Sun Oct 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.

No hazardous weather is expected at this time.

.DAYS TWO THROUGH SEVEN...Monday through Saturday.

No hazardous weather is expected at this time.

.SPOTTER INFORMATION STATEMENT...

None.

JMP

Special Weather Statement
National Weather Service Greenville-Spartanburg SC
336 PM EDT Sun Oct 3 2021

GAZ017-032000-
Habersham GA-
336 PM EDT Sun Oct 3 2021

...A THUNDERSTORM WITH FREQUENT LIGHTNING WILL IMPACT HABERSHAM
COUNTY UNTIL 400 PM EDT...

At 335 PM EDT, Doppler radar was tracking a thunderstorm with
frequent lightning 8 miles southeast of Cleveland, or 5 miles east
of Clermont, moving north at 15 mph.

Locations to be impacted include...
Clarkesville, Demorest, Alto, Baldwin, Cornelia, Raoul, Batesville,
Turnerville and Hollywood.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Frequent lightning is occurring with this storm. If outdoors, try to
get indoors or into a hard topped vehicle. Otherwise, stay away from
open areas and isolated high objects such as trees. When indoors,
stay away from windows and doors and avoid using wired electronic
devices. Do not take a shower or bath. Try to unplug unnecessary
appliances before the storm approaches.

&&

LAT...LON 3482 8365 3483 8360 3479 8356 3476 8356
      3474 8353 3473 8348 3475 8343 3473 8341
      3447 8357 3443 8362 3450 8367 3454 8362
      3460 8365 3462 8364 3465 8366 3468 8364
      3474 8362 3477 8363 3480 8368
TIME...MOT...LOC 1935Z 200DEG 12KT 3450 8368

KRENTZ

Special Weather Statement
National Weather Service Greenville-Spartanburg SC
358 PM EDT Sun Oct 3 2021

GAZ010-017-032030-
Rabun GA-Habersham GA-
358 PM EDT Sun Oct 3 2021

...A THUNDERSTORM WITH FREQUENT LIGHTNING AND TORRENTIAL RAINFALL
WILL IMPACT NORTHEASTERN HABERSHAM AND RABUN COUNTIES UNTIL 430 PM
EDT...

At 358 PM EDT, Doppler radar was tracking a thunderstorm with
frequent lightning and torrential rainfall near Clayton, or near
Tiger, moving northeast at 15 mph.

Locations to be impacted include...
Clayton, Mountain City, Tiger, Dillard, Sky Valley, Tallulah Falls,
Lake Rabun, Lake Burton, Lakemont and Tallulah Gorge State Park.

Very heavy rainfall rates up to 2 inches per hour will be possible in
these areas.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Frequent lightning is occurring with this storm. If outdoors, try to
get indoors or into a hard topped vehicle. Otherwise, stay away from
open areas and isolated high objects such as trees. When indoors,
stay away from windows and doors and avoid using wired electronic
devices. Do not take a shower or bath. Try to unplug unnecessary
appliances before the storm approaches.

&&

LAT...LON 3499 8346 3500 8327 3493 8314 3493 8316
      3492 8316 3489 8320 3488 8321 3488 8324
      3485 8325 3485 8327 3482 8327 3483 8329
      3482 8331 3481 8330 3479 8332 3476 8332
      3469 8341 3477 8362
TIME...MOT...LOC 1958Z 215DEG 13KT 3483 8341

KRENTZ

Special Weather Statement
National Weather Service Greenville-Spartanburg SC
416 PM EDT Sun Oct 3 2021

GAZ017-018-032100-
Stephens GA-Habersham GA-
416 PM EDT Sun Oct 3 2021

...A THUNDERSTORM WITH FREQUENT LIGHTNING WILL IMPACT STEPHENS AND
CENTRAL HABERSHAM COUNTIES UNTIL 500 PM EDT...

At 416 PM EDT, Doppler radar was tracking a thunderstorm with
frequent lightning 6 miles southeast of Clarkesville, or 4 miles
northeast of Mount Airy, moving east at 25 mph.

Locations to be impacted include...
Toccoa, Clarkesville, Cornelia, Baldwin, Demorest, Mount Airy,
Martin, Avalon, Tallulah Falls and Tallulah Gorge State Park.

In addition to intense lightning, very heavy rainfall rates up to 2
inches per hour will be possible in these areas.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Frequent lightning is occurring with this storm. If outdoors, try to
get indoors or into a hard topped vehicle. Otherwise, stay away from
open areas and isolated high objects such as trees. When indoors,
stay away from windows and doors and avoid using wired electronic
devices. Do not take a shower or bath. Try to unplug unnecessary
appliances before the storm approaches.

&&

LAT...LON 3464 8362 3473 8337 3472 8335 3468 8334
      3467 8331 3461 8323 3461 8316 3459 8317
      3459 8316 3458 8316 3454 8310 3448 8318
      3447 8338 3446 8340 3448 8347 3449 8353
      3448 8356
TIME...MOT...LOC 2016Z 254DEG 21KT 3455 8344

KRENTZ