Severe Thunderstorm Warning 103, NWS Greenville-Spartanburg, SC

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
148 PM EDT Fri May 22 2020

.SYNOPSIS...
An upper-level low pressure system just northwest of the region
early this morning will move away to the northeast today. A strong
disturbance rounding the south side of this system will cross the
western Carolinas and northeast Georgia late today. A strengthening
high pressure ridge will then build over the southeast through the
weekend, with warming temperatures but also afternoon and evening
thunderstorms redeveloping each day. The high pressure ridge will
dominate the southeast through much of next week.

&&

.NEAR TERM /THROUGH TONIGHT/...
130 PM Update...Convection upstream has remained intact and is now
crossing the wrn parts of the FA. Instability will be moderate,
however, these storms will remain rather organized with good support
from an ulvl s/w and a passing h3 jet core. Thus...a severe
thunderstorm watch is now in effect for most areas east of the NC
mtns. have issues a svr tstm warning for a bowing structure across
Oconee Co. Radar base velocities are not real high with this
feature, yet with wet antecedent soils, tress can be toppled with
sub-severe winds. Will likely issue convective statements/warnings
on this line as it moves east of the FA thru 00z.

1030 AM Update...Shallow convec showers and thunderstorms are
crossing into the far wrn zones currently. Not expecting much impact
with these storms outside of periodic cloud-to-ground lightning.
Still anticipating a possibly semi-organized line of storms later
this afternoon associated with a stout upper-level vort lobe. Much
will depend on the amt of instability achieved after more widespread
cloudiness spreads in during the early afternoon.

As of 635 am EDT: The Dense Fog Advisory has been expanded to
Laurens SC and Union NC through 9 am. There continues to be a race
ongoing between visibility crashing in dense fog due to the abundant
low level moisture, and mid-level clouds arriving from the west
ahead of the leading edge of the upper level forcing. There should
be a slightly longer period of areas of dense fog across the western
NC foothills and piedmont, as well as the eastern Upstate of SC,
east of a Spartanburg to Laurens line, before the clouds spill in to
improve the visibility. A dense fog advisory remains in effect for
these areas through 9 am, while an SPS has been featured for
mountain river valley fog.

Otherwise, water vapor imagery shows a deep, closed low pressure
system slowly filling over upper portions of the Ohio River Valley
early this morning. After the low clouds and fog burn off mid to
late morning, heating and instability will rebound quickly through
the afternoon hours. As the upper jetlet associated with the upper
low lifts northeast today, improving upper divergence will cross the
western Carolinas during the afternoon and evening hours. In
addition, embedded H5 vorticity lobes south of the departing upper
low will cross the heart of the forecast area from 18Z this
afternoon through about 03Z this evening. This should provide plenty
of forcing for convection during the afternoon and evening hours.
Mid-level lapse rates should increase to about 6.5 deg C/km, SBCAPE
values should rise above 2000 J/kg, especially over the southern
half of the forecast area. Sfc to 3 km shear values should reach 40
to 45 kt late in the day and likely peak near I-77 by early evening.
The marginal severe threat thus appears warranted across the
forecast area, with perhaps the greatest risk near the I-85 corridor
where instability and shear will best overlap to produce a damaging
wind/isolated tornado threat.

The filling upper low will lift steadily away through the Mid-
Atlantic tonight, with a shallow upper ridge beginning to build over
the southern Appalachians. Showers could persist into the nighttime
hours given the lingering low-level moisture, but thunder chances
will steadily diminish with the loss of instability and departing
upper forcing. Anticipate a smaller than climo diurnal range on
temps through the near term.

&&

.SHORT TERM /SATURDAY THROUGH SUNDAY/...
As of 330 am EDT Friday: A 500 mb ridge axis will strengthen over
the southeast through the weekend, with 585 dm heights on Saturday
rising to 586 dm by Sunday afternoon. With the ridge axis setting up
just west of the mountains Saturday afternoon, there is some
potential for upstream convection to ride down the ridge and across
the northern tier of the forecast area late in the day. Piedmont
locations should see 2500 J/kg of sbCAPE late day with heating, plus
the northern tier could experience 30+ kt of shear. Timing any MCS
development or movement will be challenging, so the forecast will
follow mainly a diurnal peak with instability, especially with lapse
rates steepening up over the mountains Saturday afternoon.

With capping under the ridge still fairly limited through late
weekend, ridge top convection will likely develop again with heating
Sunday afternoon. SBCAPE values should rebound to 2000+ again late
in the day, and a surface backdoor cold front may approach from the
northeast very late Sunday. Steering flow will be quite weak on
Sunday, meaning any convection could pose local hydro issues from
slowly moving storms. Anticipate max temps rising to some 5 to 10
degrees above climo through the weekend.

&&

.LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/...
As of 330 AM Friday: A blocky, amplified pattern will develop across
the CONUS thru the medium range, as an upper ridge closes off over
the Mid-Atlantic, while an upper low develops over the Southern
Plains. This will keep a persistent easterly to southeasterly deep-
layer flow atop the forecast area thru most of next week. This
results in slightly above normal temps, despite plenty of cloudiness
from persistent Atlantic moisture fetch across the region. Generally
isolated to scattered diurnal convection is expected each day,
especially in the high terrain, as we enter more typical late-spring
pulse convective season. The higher PWAT plume will stay west of the
area, so heavy rain threat should be localized to slow-moving or
training convection. Severe threat looks isolated.

&&

.AVIATION /18Z FRIDAY THROUGH WEDNESDAY/...
At KCLT and Elsewhere: A mixed bag in the TAFs with a line of convec
storms moving quickly across the FA this afternoon. Have timings for
TS and VCTS with some lowering CIGs into MVFR mainly across the the
mtns this afternoon and then again across the non/mtns late within
PROB30s for general thunder and precip trailing the main MCS this
afternoon/evening. Winds will remain fairly low-end outside of gusty
storms as a llvl ridge builds in from the east.

Outlook: Afternoon to evening showers and thunderstorms will be
possible over the weekend and into early next week. Restrictions are
also possible each morning from low clouds and fog and again later
in the day under any thunderstorms.

Confidence Table...

            17-23Z        23-05Z        05-11Z        11-12Z
KCLT       High 100%     High 100%     High 100%     High  89%
KGSP       Med   75%     High 100%     High 100%     High 100%
KAVL       Med   69%     Med   60%     High 100%     Med   66%
KHKY       High 100%     Med   65%     Med   75%     Low   53%
KGMU       High  87%     High 100%     High 100%     High 100%
KAND       High  81%     High 100%     High 100%     High 100%

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...HG
NEAR TERM...HG/SBK
SHORT TERM...HG
LONG TERM...ARK
AVIATION...SBK

Hazardous Weather Outlook
National Weather Service Greenville-Spartanburg SC
133 PM EDT Fri May 22 2020

GAZ010-017-018-026-028-029-NCZ036-037-056-057-068>072-082-503>510-
SCZ001>014-019-231745-
Rabun-Habersham-Stephens-Franklin-Hart-Elbert-Iredell-Davie-Catawba-
Rowan-Cleveland-Lincoln-Gaston-Mecklenburg-Cabarrus-Union NC-
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-
133 PM EDT Fri May 22 2020

...SEVERE THUNDERSTORM WATCH 202 IN EFFECT UNTIL 8 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.

.DAYS TWO THROUGH SEVEN...Saturday through Thursday.

No hazardous weather is 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.

NCZ033-035-048>053-058-059-062>065-501-502-231745-
Avery-Alexander-Madison-Yancey-Mitchell-Swain-Haywood-Buncombe-
Graham-Northern Jackson-Macon-Southern Jackson-Transylvania-
Henderson-Caldwell Mountains-Greater Caldwell-
133 PM EDT Fri May 22 2020

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

.DAY ONE...This afternoon and tonight.

Thunderstorms are possible afternoon and evening. Cloud to ground
lightning and locally heavy rainfall can be expected with any of
these thunderstorms. The thunderstorms may also produce very gusty
winds, and damaging gusts to 60 mph will be possible in a couple
storms. Flash flooding from torrential rainfall is also possible.

.DAYS TWO THROUGH SEVEN...Saturday through Thursday.

No hazardous weather is expected at this time.

.SPOTTER INFORMATION STATEMENT...

None.

8

Special Weather Statement
National Weather Service Greenville-Spartanburg SC
107 PM EDT Fri May 22 2020

GAZ010-NCZ062>064-SCZ001-002-004-221745-
Rabun GA-Transylvania NC-Southern Jackson NC-Macon NC-
Pickens Mountains SC-Greater Oconee SC-Oconee Mountains SC-
107 PM EDT Fri May 22 2020

...A STRONG THUNDERSTORM WILL IMPACT RABUN...SOUTHEASTERN MACON...
SOUTHWESTERN TRANSYLVANIA...SOUTHEASTERN JACKSON...NORTHWESTERN
PICKENS AND OCONEE COUNTIES UNTIL 145 PM EDT...

At 106 PM EDT, Doppler radar was tracking a strong thunderstorm 4
miles southwest of Clayton, or near Tiger, moving east at 40 mph.

Locations to be impacted include...
Seneca, Walhalla, Clayton, Highlands, Mountain City, Tiger, Dillard,
Sky Valley, Cashiers and Salem.

Wind gusts up to 50 mph, pea size hail and very heavy rainfall rates
up to 2 inches per hour will be possible in these areas.

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 3517 8285 3482 8287 3481 8289 3478 8288
      3474 8290 3474 8288 3468 8288 3471 8335
      3473 8338 3473 8341 3475 8343 3473 8348
      3474 8352 3499 8355 3500 8348 3500 8352
      3502 8352 3504 8356 3506 8356
TIME...MOT...LOC 1706Z 266DEG 33KT 3483 8345

RM

Special Weather Statement
National Weather Service Greenville-Spartanburg SC
134 PM EDT Fri May 22 2020

GAZ018-026-028-SCZ001-004-005-010-221800-
Hart GA-Franklin GA-Stephens GA-Greater Pickens SC-Greater Oconee SC-
Anderson SC-Oconee Mountains SC-
134 PM EDT Fri May 22 2020

...STRONG THUNDERSTORMS WILL IMPACT FRANKLIN...STEPHENS...
NORTHWESTERN HART...NORTHWESTERN ANDERSON...SOUTHWESTERN PICKENS AND
OCONEE COUNTIES UNTIL 200 PM EDT...

At 134 PM EDT, Doppler radar indicated strong thunderstorms along a
line extending from 8 miles west of Walhalla to 5 miles north of
Homer, and moving east at 40 mph.

Locations to be impacted include...
Clemson, Toccoa, Seneca, Walhalla, Carnesville, Hartwell, Central,
Pendleton, Liberty and Westminster.

Wind gusts up to 50 mph, pea size hail and very heavy rainfall rates
up to 2 inches per hour will be possible in these areas.

Doppler radar indicates weak rotation with These storms. 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.

A Severe Thunderstorm Watch remains in effect until 800 PM EDT for
northeastern Georgia...and Upstate South Carolina.

LAT...LON 3436 8339 3443 8338 3446 8340 3448 8346
      3453 8344 3481 8320 3483 8290 3481 8290
      3483 8284 3485 8262 3432 8297
TIME...MOT...LOC 1734Z 275DEG 35KT 3477 8320 3441 8353

RM

Special Weather Statement
National Weather Service Greenville-Spartanburg SC
200 PM EDT Fri May 22 2020

GAZ018-026-028-029-SCZ001-004>006-010-221845-
Elbert GA-Hart GA-Franklin GA-Stephens GA-Greater Pickens SC-
Greater Oconee SC-Anderson SC-Oconee Mountains SC-
Greater Greenville SC-
200 PM EDT Fri May 22 2020

...STRONG THUNDERSTORMS WILL IMPACT FRANKLIN...STEPHENS...
NORTHWESTERN ELBERT...HART...CENTRAL GREENVILLE...ANDERSON...SOUTHERN
PICKENS AND SOUTHERN OCONEE COUNTIES UNTIL 245 PM EDT...

At 159 PM EDT, Doppler radar indicated strong thunderstorms along a
line extending from 8 miles north of Clemson to 4 miles northwest of
Carnesville, and moving east at 40 mph.

Locations to be impacted include...
Anderson, Easley, Clemson, Seneca, Hartwell, Carnesville, Greenville
Downtown, Toccoa, Greenville Eastside and West Greenville.

Wind gusts up to 50 mph, pea size hail and very heavy rainfall rates
up to 2 inches per hour will be possible in these areas.

Doppler radar indicates weak rotation with These storms. 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.

A Severe Thunderstorm Watch remains in effect until 800 PM EDT for
northeastern Georgia...and Upstate South Carolina.

LAT...LON 3417 8310 3423 8308 3427 8312 3424 8317
      3424 8325 3426 8330 3423 8335 3426 8334
      3433 8339 3443 8338 3446 8340 3448 8343
      3450 8343 3485 8290 3481 8290 3486 8280
      3485 8229 3421 8274 3416 8276 3415 8306
TIME...MOT...LOC 1759Z 268DEG 34KT 3479 8286 3443 8327

RM