Special Weather Statement, NWS Greenville-Spartanburg, SC

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
155 PM EDT Tue May 4 2021

.SYNOPSIS...
Expect chances for showers and thunderstorms to continue across the
region until a cold front crosses from the west on Wednesday,
After the front passes, high pressure will bring cooler
temperatures into Saturday.  The high will shift to our east over
the weekend, resulting in warmer temperatures into early next week.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 950 AM EDT Tuesday: The latest RADAR mosaic has an impressive
looking line of thunderstorms pushing east across central TN and
some weaker sct showers/thunderstorms moving over our western-most
zones. SPC just added Graham, Swain, and Macon Counties to a Severe
Thunderstorm Watch that runs until 1 PM, however the severe potential
certainly looks better to their west.

Otherwise, the main concern is another round of strong to severe
thunderstorms across the CWA. Thus far, the model guidance has not
revealed much consistency in how the convection will evolve today,
other than to show we will not be in quite the same shear/buoyancy
parameter space as we were yesterday. The convection-allowing models
are struggling with the development/evolution of the convection (or
lack thereof) over the TN Valley/Cumberland Plateau region, which
hampers the confidence across our forecast area. The HREF is
unimpressed with our chances for severe weather, with the better
updraft potential mainly to our south this afternoon. One wonders if
the CAMS, having trouble with having too much early morning
convection, are underdoing the amount of potential for buoyancy this
afternoon. The 06Z RAP for example still manages to develop 2000-
2500 J/kg of mlCAPE east of the Blue Ridge this afternoon, although
shear is not nearly as strong yesterday and is more unidirectional.
Readers will note how almost all the forecast area has been removed
from the Slight Risk for today. However, one should never say never
to scattered severe storms with the amount of CAPE and shear we
should retain this afternoon, and we will be on the lookout for
them. Severe or not, coverage should be up in the numerous range
today and into the early part of the evening. The synoptic scale
models might be overdoing the upscale growth potential this evening
with the convection moving in from the west, so the precip probs
will be tailed off after 00Z for the time being, eventually dropping
back to the mtns overnight, with some potential for more storms
reaching the NC mtns toward daybreak Wednesday, ahead of the
approaching cold front. The flash flood potential will be higher
today after the rains of yesterday, but still not high enough to
consider any watches. Temps should make a rebound back above normal
today.

&&

.SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/...
As of 130 PM EDT Tuesday: Weakening low pressure is already passing
well to our north and off the east coast on Wednesday evening,
dragging a trailing cold front out of the Carolinas overnight.
Moisture appears lacking with this system, however, with all the
deterministic models depicting better PWATs mainly to our north.
By Thursday morning after sunrise, the front should have cleared
our CWA anyway, and precipitation should have let up except
perhaps for a few upslope areas in the western Appalachians.
Dry northwest flow takes hold from there.

Conditions should remain calm on Thursday, with a zonal, undisturbed
500mb pattern persisting through the day, until a a deepening
shortwave digs out of the Midwest.  This should provide modest
midlevel forcing Thursday night, tapering off Friday morning as the
vort max passes over our CWA and heights begin to recover again.
Precip associated with this fropa will be severely limited, owing to
the moisture-starved environment in which that forcing takes place.
Moreover, despite temps dropping into the mid/upper 30s in a few
high-elevation spots in the mountains, a steady wind paired with
a few weak gusts should prevent much frost formation.

Heights continue to rise on Friday as northwesterly CAA continues
and high pressure builds into the area.  We should transition to
a weak ridging regime for the weekend, allowing temps to creep
back toward normal, although still staying below normal through
Friday evening.

&&

.LONG TERM /FRIDAY THROUGH TUESDAY/...
As of 145 PM EDT Tuesday: Dry high pressure continues to dominate
the forecast on Saturday as weak ridging pushes through the eastern
U.S.  We'll see a wind shift to southerly return flow early Sunday,
as the high center drifts east of us and meanders off the coast.
So, moisture content on Sunday will be greater than on the previous
two days, as a lifting warm front induces modest moisture advection
into the region.  Sunday night, a shortwave pushes across the
region, and heights begin to fall again.  We should see a cold
fropa Sunday night or Monday morning, which will yield our next
opportunity for moderate PoPs, after which the boundary will stall
and provide a focus for additional activity later in the week.
Guidance has not yet reached a consensus this far out, but in broad
strokes we can expect the boundary to meander north and south,
allowing for another potentially active week.

Temps will creep upward over the weekend, returning to near-
or slightly above-normal by Sunday afternoon.  Saturday morning
especially may present a frost threat in the mountains, as temps
at high elevations may drop into the 30s beneath a fairly calm
prevailing wind.

&&

.AVIATION /18Z TUESDAY THROUGH SUNDAY/...
At KCLT and elsewhere: Vrb ceiling restrictions will continue thru
much of the 18z taf period as the bndy layer will remain particularly
moist. All taf sites will likely see another round of showers and
thunderstorms, most likely during the middle to late afternoon, which
are largely handled with TEMPO groups. It appears that we'll see a
break in the action during the later in the aftn or early evening
where conditions may improve to VFR, but then another round of
convection develops this evening which are handled with another
round of TEMPOs. Winds will remain SLY to SWLY thru the period,
with sporadic gusts this aftn and again tomorrow aftn, especially
in the vicinity of any thunderstorms. There is some indication of
cig/visby restrictions redeveloping before daybreak tomorrow, but
confidence remains low at this time. For the time being, I kept an
MVFR cig at the Upstate sites from roughly 08 to 14z.

Outlook: The chances for restrictions will persist thru Wednesday
as a cold front moves into the area and crosses the region. Another
lull in convective activity is expected for the end of the week.

Confidence Table...

            18-24Z        00-06Z        06-12Z        12-18Z
KCLT       High  97%     High  93%     High  90%     High  97%
KGSP       High  96%     High  94%     Med   79%     High  94%
KAVL       High  95%     High  98%     High  96%     High  94%
KHKY       High  95%     High  90%     High  95%     High 100%
KGMU       High  85%     High  94%     High  83%     High  96%
KAND       High  91%     High  94%     Med   72%     High  85%

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

&&

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

&&

SYNOPSIS...ARK
NEAR TERM...JPT
SHORT TERM...ARK
LONG TERM...ARK
AVIATION...JPT

Hazardous Weather Outlook
National Weather Service Greenville-Spartanburg SC
136 PM EDT Tue May 4 2021

GAZ010-017-018-026-028-029-NCZ033-035-036-048>053-056-058-059-
062>065-068>070-501>510-SCZ001>008-010>013-019-050400-
Rabun-Habersham-Stephens-Franklin-Hart-Elbert-Avery-Alexander-
Iredell-Madison-Yancey-Mitchell-Swain-Haywood-Buncombe-Catawba-
Graham-Northern Jackson-Macon-Southern Jackson-Transylvania-
Henderson-Cleveland-Lincoln-Gaston-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-Anderson-Abbeville-Laurens-
Union SC-Greenwood-
136 PM EDT Tue May 4 2021

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

.DAY ONE...This afternoon and tonight.

A cold front approaching from the west will be the trigger for
another round of strong to severe thunderstorms during mainly the
afternoon hours today. The main threats will be damaging wind gusts
and large hail. An isolated brief tornado cannot be ruled out across
the southern Piedmont. The storms will increase the threat for
isolated flash flooding as well across areas that experience multiple
rounds of rainfall.

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

Hazardous weather is not expected at this time.

.SPOTTER INFORMATION STATEMENT...

Spotter activation may be needed. Please relay any information about
observed severe weather to the NWS while following all local, state,
and CDC guidelines.

NCZ037-057-071-072-082-SCZ009-014-050400-
Davie-Rowan-Mecklenburg-Cabarrus-Union NC-York-Chester-
136 PM EDT Tue May 4 2021

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

.DAY ONE...This afternoon and tonight.

A cold front approaching from the west will be the trigger for
another round of strong to severe thunderstorms during mainly the
afternoon hours today. The main threats will be damaging wind gusts
and large hail. An isolated brief tornado cannot be ruled out across
the southern Piedmont. The storms will increase the threat for
isolated flash flooding as well across areas that experience multiple
rounds of rainfall.

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

The cold front could trigger isolated severe thunderstorms along and
east of the I-77 corridor again on Wednesday as it crosses the
region.

.SPOTTER INFORMATION STATEMENT...

Spotter activation may be needed. Please relay any information about
observed severe weather to the NWS while following all local, state,
and CDC guidelines.

Special Weather Statement
National Weather Service Greenville-Spartanburg SC
1236 PM EDT Tue May 4 2021

SCZ005-006-010-041700-
Greater Pickens SC-Anderson SC-Greater Greenville SC-
1236 PM EDT Tue May 4 2021

...A STRONG THUNDERSTORM WILL IMPACT EAST CENTRAL GREENVILLE...NORTH
CENTRAL ANDERSON AND EAST CENTRAL PICKENS COUNTIES UNTIL 100 PM
EDT...

At 1236 PM EDT, Doppler radar was tracking a strong thunderstorm 4
miles east of Easley, or near Powdersville, moving northeast at 35
mph.

Locations to be impacted include... Greenville, Easley, Greer,
Mauldin, Taylors, Berea, Five Forks and Welcome.

Wind gusts up to 40 mph and pea size hail will be possible in these
areas.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

The combination of gusty winds and saturated soil conditions will
cause scattered trees and power lines to fall. Seek shelter inside an
interior room.

This storm may intensify, so be certain to monitor local radio and tv
stations, as well as local cable tv outlets for additional
information and possible warnings from the National Weather Service.

&&

LAT...LON 3483 8263 3503 8226 3495 8222 3485 8223
      3485 8222 3483 8219 3481 8217 3473 8257
TIME...MOT...LOC 1636Z 245DEG 32KT 3481 8252

8

Special Weather Statement
National Weather Service Greenville-Spartanburg SC
123 PM EDT Tue May 4 2021

SCZ001>006-041800-
Pickens Mountains SC-Greater Pickens SC-Greater Oconee SC-
Oconee Mountains SC-Greenville Mountains SC-Greater Greenville SC-
123 PM EDT Tue May 4 2021

...A STRONG THUNDERSTORM WILL IMPACT NORTHWESTERN GREENVILLE...
PICKENS AND EAST CENTRAL OCONEE COUNTIES UNTIL 200 PM EDT...

At 123 PM EDT, Doppler radar was tracking a strong thunderstorm 10
miles northeast of Walhalla, or near Lake Keowee, moving northeast at
40 mph.

Locations to be impacted include...
Pickens, Six Mile, Salem, Lake Keowee, Jocassee Gorges, Keowee
Toxaway State Park, Table Rock State Park, Caesars Head State Park,
Travelers Rest and Slater-Marietta.

Wind gusts up to 45 mph and pea size hail will be possible in these
areas.

LAT...LON 3485 8303 3510 8272 3510 8269 3511 8270
      3513 8268 3512 8267 3512 8266 3513 8264
      3513 8263 3514 8260 3495 8243 3471 8290
TIME...MOT...LOC 1723Z 232DEG 34KT 3483 8290

WJM

Special Weather Statement
National Weather Service Greenville-Spartanburg SC
219 PM EDT Tue May 4 2021

SCZ007-008-013-041845-
Cherokee SC-Union SC-Spartanburg SC-
219 PM EDT Tue May 4 2021

...A STRONG THUNDERSTORM WILL IMPACT CENTRAL SPARTANBURG...
SOUTHWESTERN CHEROKEE AND NORTHERN UNION COUNTIES UNTIL 245 PM EDT...

At 217 PM EDT, Doppler radar was tracking a strong thunderstorm 7
miles south of Spartanburg, or over Moore, moving east at 35 mph.

Locations to be impacted include...
Spartanburg, Woodruff, Pacolet, Roebuck, Jonesville, Pacolet Mills,
Croft State Park, Moore, Cedar Springs and Reidville.

Wind gusts up to 50 mph will be possible in these areas.

LAT...LON 3472 8204 3490 8209 3504 8159 3478 8151
TIME...MOT...LOC 1817Z 256DEG 32KT 3484 8198

WJM

Special Weather Statement
National Weather Service Greenville-Spartanburg SC
224 PM EDT Tue May 4 2021

GAZ018-026-028-SCZ004-010-041900-
Hart GA-Franklin GA-Stephens GA-Greater Oconee SC-Anderson SC-
224 PM EDT Tue May 4 2021

...A STRONG THUNDERSTORM WILL IMPACT NORTHEASTERN FRANKLIN...
SOUTHEASTERN STEPHENS...NORTHERN HART...SOUTHWESTERN ANDERSON AND
SOUTH CENTRAL OCONEE COUNTIES UNTIL 300 PM EDT...

At 224 PM EDT, Doppler radar was tracking a strong thunderstorm 5
miles northeast of Carnesville, or near Martin, moving east at 50
mph.

Locations to be impacted include...
Hartwell, Carnesville, Reed Creek, Lavonia, Gumlog, Bowersville,
Martin, Avalon, Tugaloo State Park and Lake Hartwell.

Wind gusts up to 40 mph will be possible in these areas.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

This storm may intensify, so be certain to monitor local radio and tv
stations, as well as local cable tv outlets for additional
information and possible warnings from the National Weather Service.

Doppler radar indicates weak rotation with this storm. Spin-up of a
very brief, weak tornado cannot be ruled out. Be prepared to take
immediate action if a tornado is sighted or a Tornado Warning is
issued.

&&

LAT...LON 3437 8329 3450 8329 3457 8276 3431 8276
TIME...MOT...LOC 1824Z 269DEG 42KT 3443 8317

8

Special Weather Statement
National Weather Service Greenville-Spartanburg SC
232 PM EDT Tue May 4 2021

GAZ026-028-029-041900-
Elbert GA-Hart GA-Franklin GA-
232 PM EDT Tue May 4 2021

...A STRONG THUNDERSTORM WILL IMPACT SOUTHERN FRANKLIN...NORTHWESTERN
ELBERT AND SOUTHERN HART COUNTIES UNTIL 300 PM EDT...

At 232 PM EDT, Doppler radar was tracking a strong thunderstorm 6
miles south of Carnesville, or 5 miles west of Victoria Bryant State
Park, moving east at 30 mph.

Locations to be impacted include...
Hartwell, Carnesville, Elberton, Royston, Bowman, Canon, Franklin
Springs, Victoria Bryant State Park, Bowersville and Dewy Rose.

Wind gusts up to 40 mph will be possible in these areas.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

The combination of gusty winds and saturated soil conditions will
cause scattered trees and power lines to fall. Seek shelter inside an
interior room.

This storm may intensify, so be certain to monitor local radio and tv
stations, as well as local cable tv outlets for additional
information and possible warnings from the National Weather Service.

&&

LAT...LON 3414 8306 3415 8307 3416 8310 3417 8310
      3423 8308 3427 8312 3424 8317 3425 8320
      3424 8325 3426 8330 3423 8335 3424 8335
      3425 8334 3436 8334 3438 8285 3411 8288
TIME...MOT...LOC 1832Z 274DEG 27KT 3428 8325

8