Special Weather Statement, NWS Greenville-Spartanburg, SC

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
740 PM EDT Mon Aug 7 2017

.SYNOPSIS...
A warm front will remain north of the area tonight as low pressure
moves from Tennessee to Virginia. The low pressure will move off
the New England Coast and pull the front back south over the forecast
area as a cold front tomorrow. The front is expected to stall
again across our region and remain through the end of the week,
with deep moisture and periods of heavy rain likely.

&&

.NEAR TERM /THROUGH TUESDAY/...
As of 740 PM EDT Monday:  Not much change in the immediate near term
as multiple rounds of sct/num convection move across the region,
with the next round expected to enter the NE GA zones within hour.
Thus did hold onto likely pops for a bit longer over the western
tier of the fcst area, as well as the far eastern tier as the
initial round of shra/tsra exits eastward.  Latest SPC mesoanalysis
continues to indicate a rather sharp instability gradient south of
I85, therefore think the deepest/strongest convection will occur
there, thus a strong/severe storm is not to be ruled out over the
next hour or two.  Elsewhere as far as threats, still thinking
general thunder with brief gusty winds and heavy downpours.
Otherwise, tweaked t/td and sky trends to align with recent obs and
left the remainder of the fcst as it was for this update.

As of 230 PM: Muggy, unsettled weather conditions expected thru the
Near Term, as a cold front approaches from the north. A positively
tilted upper trough will dig over the Ohio Valley tonight, while
a sfc low pressure wave tracks across the Central Appalachians.
Forecast soundings show very moist air mass in place, with low LFC
heights and high freezing levels. Bulk shear is weakening and upper
forcing with the upper trough doesn't look strong enough to make for
real robust updrafts, as SBCAPE is only around 1500 J/kg. Where CAPE
is a little higher over the Midlands and Low Country, there are a
few strong storms. So I think severe threat is fairly low. The main
threat tonight into Tuesday will be locally heavy rain. But even
with this, I don't think things should get too out of hand. Will
continue to mention heavy rain in the HWO, given the very moist
air mass, and possibly some training convection. The highest QPF
is expected to be in the western NC mountains, where WSW upslope
flow helps enhance amounts of 1-2". The rest of the area should
see generally 0.5 to 0.75" amounts.

Overnight, convection should generally wane, but guidance does show
additional precip moving into the mountains from the west. This
activity should be fairly light, but embedded heavy downpours will
be possible. Temps will be slightly above normal under plenty of
cloud cover.

Tuesday, the overnight band of precip should continue to weaken as
it enters the piedmont early in the morning. At the surface, the
cold front should push in from the north and is expected to reach
the southern edge of the CWA by late morning. The NC mountains may
clear out enough for showers and storms to develop by early AFTN,
while the piedmont will take longer to see much clear behind the
front. Temps will be well below normal across the area under cloud
cover, closer to normal in the mountains with some clearing. Deep
convection, mainly showers and garden-variety tstms will be mainly
confined to the Blue Ridge. A small heavy rain threat will continue
due to the very moist air mass still in place.

&&

.SHORT TERM /TUESDAY NIGHT THROUGH THURSDAY/...
As of 2:30 PM EDT Monday:  A post frontal trough, or secondary wind
shift line, will ease through our forecast area Tuesday evening. We
will be taking POPS down to slight chance, or lower by morning.

It appears the model suite is allowing a surface high to extend from
Illinois to Pennsylvania, and south into the Carolina's for mid
week. It almost has a mini wedge configuration. Low level moisture
should be abundant nevertheless, and we will start the diurnal
cycle for POPS, perhaps slightly abvoe average.

We start with a minimum in POPS Wednesday evening, but the upper
level flow starts to back and allow a return of moisture. Also a
wave train of vort maxes are embedded in the flow. The POPS for
Wednesday night still remain in the chance category, but edge up.

A bit more sharpening of upper level features Thursday should signal
an uptick in POP configuration, as a result we have brought values
up accordingly.

Overall through this portion of the forecast cycle, it appears to be
a lull in the amount and coverage of precipitation, considering the
constuction of the entire forecast package. However, we still have
to be on guard for heavy rain potential, although at least in this
part of the forecast cycle it appears to have eased somewhat.

As far as any severe potential, pulse type storms certainly look
possible Wednesday. Thursday we will probably begin having the
influence of some larger synoptic forcing.

Temperatures for this part of the forecast should remain be average,
which remains in line with the previous forecast and new data.

&&

.LONG TERM /THURSDAY NIGHT THROUGH MONDAY/...
As of 210 PM EDT Monday: the extended fcst picks up at 00z on
Friday with a very broad, low amplitude upper trof centered over
Eastern Canada and upper ridging persisting over the Western CONUS
and well to our east over the sub-tropical Atlantic. As we move
into the weekend, a more amplified upper trof begins to dig down
over the Northern Plains and Western Great Lakes as the upper ridge
persists over the Western CONUS. The upper trof axis is still not
expected to reach our area until the very end of the period, early
next week.

At the sfc, moist SLY return flow will be in place over the region
on Friday as a low slowly moves eastward across the Great Lakes and
brings its associated weak cold front towards the fcst area on Sat.
This scenario is about 24 hours faster than model runs this time
yesterday with the ECMWF being more progressive with the front than
the GFS. Beyond this point, the pattern evolution becomes more ambiguous
with the ECMWF trying to develop a secondary low in the wake of the
fropa late Sunday into early Monday and then quickly move that low
up the New England Coast. The GFS also tries to develop some sort of
weak system during this time frame, but it's not as coherent as the
ECMWF. Regardless, both models keep deeper moisture over the fcst
area thru the end of the period. As for the sensible fcst, precip
chances will remain elevated thru the period with high-end chance
to low-end likely PoPs each day and broken to overcast cloud cover.
The potential for isolated to widespread flooding remains elevated
with precipitable water fcst values 1 to 2 standard deviations above
normal thru most of the period. With the ample cloud cover expected,
high temps should remain a few degrees below normal with low temps
right around normal.

&&

.AVIATION /00Z TUESDAY THROUGH SATURDAY/...
At KCLT and Elsewhere: A mixture of VFR/MVFR and IFR likely at all
sites through this taf cycle as a warm/moist airmass remains across
the region while a quasistationary frontal axis sits just to the
nw.  With that, multiple rounds of convection are expected this
evening/tonight with tsra possible at the SC sites, likely weakening
to only shra when reaching the NC sites.  Therefore kept any ts
wording removed from KCLT, with only vcts for a few more hours at
the KHKY/KAVL, while holding on to vcts a bit longer at the SC
locales.  Otherwise, low VFR cigs will prevail outside of any
heavier convection through much of the evening/overnight before the
aforementioned stationary front shifts southward as a cold front,
likely moving into the NC high terrain in the 08z-10z time frame.
Cigs are expected to lower further with MVFR decks possible at all
locales ahead of and along the front as it slowly moves through the
region.  Precipitation will also be possible, however confidence in
timing/placement is low, therefore sites see only prob30s for such
with timing based on camguide.  The front will begin to clear the
region late in the period with sites recovering to VFR and drying
out from west to east, with winds veering nwly/nly post fropa.  The
only exception being at KAVL where guidance favors enough
destabilization behind the front to warrant a mention of tsra in a
prob30 during the afternoon hours.

Outlook: Unsettled conditions continue through most of the week
as a frontal boundary remains nearby, moisture pools, and a series
of upper level waves pass overhead. Restrictions will be possible
with any showers and thunderstorms. Fog and low clouds may develop
each morning around daybreak, mainly in the mtn valleys but also
in areas that receive heavy rainfall the day before.

Confidence Table...

            23-05Z        05-11Z        11-17Z        17-18Z
KCLT       Low   55%     Low   55%     Low   48%     High  81%
KGSP       High 100%     High 100%     High  95%     High  87%
KAVL       High  94%     Med   78%     Low   31%     High  81%
KHKY       High 100%     Low   55%     Med   60%     Med   69%
KGMU       High 100%     High 100%     High  95%     High  81%
KAND       High 100%     High 100%     Low   43%     High  81%

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

www.weather.gov/gsp/aviation

&&

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

&&

SYNOPSIS...JPT
NEAR TERM...ARK/CDG
SHORT TERM...TS
LONG TERM...JPT
AVIATION...CDG

Hazardous Weather Outlook
National Weather Service Greenville-Spartanburg SC
458 PM EDT Mon Aug 7 2017

GAZ010-017-018-026-028-029-NCZ033-035>037-048>053-056>059-062>065-
068>072-082-501>510-SCZ001>014-019-081100-
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-
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-Chester-Greenwood-
458 PM EDT Mon Aug 7 2017

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

.DAY ONE...Tonight.

Scattered to numerous showers and thunderstorms will periodically
move across the area tonight. The potential exists for these storms
to produce torrential rainfall. Some areas may experience multiple
rounds of such storms, resulting in locally significant accumulation
and possibly flash flooding.

In addition, a few of the storms could become severe with damaging
downburst winds the main threat. Cloud-to-ground lightning will be
noted as well. Move to a place of safety if storms approach.

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

..Tuesday...Heavy rain possible. Numerous showers and thunderstorms
are expected again. This will keep the threat for heavy rainfall in
place across the area.
..Wednesday...No hazardous weather is expected at this time.
..Thursday...No hazardous weather is expected at this time.
..Friday...No hazardous weather is expected at this time.
..Saturday...No hazardous weather is expected at this time.
..Sunday...No hazardous weather is expected at this time.

.SPOTTER INFORMATION STATEMENT...

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

Sturey

Special Weather Statement
National Weather Service Greenville-Spartanburg SC
902 PM EDT MON AUG 7 2017

GAZ010-017-018-026-SCZ001-080130-
Franklin GA-Rabun GA-Stephens GA-Habersham GA-Oconee Mountains SC-
902 PM EDT MON AUG 7 2017

...STRONG THUNDERSTORMS WILL IMPACT NORTHWESTERN FRANKLIN...
STEPHENS...HABERSHAM...SOUTH CENTRAL RABUN AND SOUTHWESTERN OCONEE
COUNTIES UNTIL 930 PM EDT...

At 902 PM EDT, Doppler radar indicated strong thunderstorms along a
line extending from 6 miles north of Clarkesville to 9 miles
northwest of Homer, and moving east at 30 mph.

Locations to be impacted include...
Toccoa, Walhalla, Clarkesville, Cornelia, Baldwin, Demorest, Mount
Airy, Alto, Avalon and Tallulah Falls.

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

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Gusty winds can blow down trees that are dead, or that have weakened
root systems. Outdoor furniture and similar items can be tossed
around if not anchored. Seek shelter indoors.

&&

LAT...LON 3454 8362 3458 8364 3477 8355 3479 8303
      3463 8312 3460 8317 3458 8315 3433 8329
      3436 8339 3443 8338 3446 8340 3447 8342
      3449 8354 3443 8362 3451 8367
TIME...MOT...LOC 0102Z 277DEG 25KT 3470 8349 3445 8361

HG

Special Weather Statement
National Weather Service Greenville-Spartanburg SC
920 PM EDT MON AUG 7 2017

SCZ008-009-013-014-080145-
York SC-Cherokee SC-Union SC-Chester SC-
920 PM EDT MON AUG 7 2017

...STRONG THUNDERSTORMS WILL IMPACT WESTERN CHESTER...WESTERN YORK...
SOUTHEASTERN CHEROKEE AND UNION COUNTIES UNTIL 945 PM EDT...

At 919 PM EDT, Doppler radar indicated strong thunderstorms along a
line extending from 11 miles east of Spartanburg to 6 miles west of
Union to 16 miles northeast of Laurens, and moving east at 35 mph.

Locations to be impacted include...
Union, Monarch Mill, Buffalo, Jonesville, Lockhart, Sharon, Carlisle,
Hickory Grove, Smyrna and Rose Hill State Park.

Wind gusts up to 40 mph and very heavy rainfall rates of 1 to 2
inches per hour will be possible in these areas.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Gusty winds can blow down trees that are dead, or that have weakened
root systems. Outdoor furniture and similar items can be tossed
around if not anchored. Seek shelter indoors.

&&

LAT...LON 3458 8181 3460 8184 3459 8185 3465 8184
      3473 8180 3477 8180 3483 8179 3491 8171
      3493 8174 3493 8176 3495 8176 3510 8127
      3483 8126 3459 8139 3457 8177
TIME...MOT...LOC 0119Z 257DEG 30KT 3488 8174 3475 8173 3464 8179

HG

Special Weather Statement
National Weather Service Greenville-Spartanburg SC
938 PM EDT MON AUG 7 2017

SCZ008-009-013-080215-
York SC-Cherokee SC-Union SC-
938 PM EDT MON AUG 7 2017

...A STRONG THUNDERSTORM WILL IMPACT WESTERN YORK...SOUTHEASTERN
CHEROKEE AND NORTHEASTERN UNION COUNTIES UNTIL 1015 PM EDT...

At 938 PM EDT, Doppler radar was tracking a strong thunderstorm 12
miles southeast of Gaffney, or 8 miles northeast of Jonesville,
moving northeast at 45 mph.

Locations to be impacted include...
York, Clover, Newport, Sharon, Hickory Grove, Smyrna, Kings Mountain
State Park, Bullock Creek, Saratt and Kings Creek.

Wind gusts up to 45 mph and very heavy rainfall rates of 1 to 2
inches per hour will be possible in these areas.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Gusty winds can blow down trees that are dead, or that have weakened
root systems. Outdoor furniture and similar items can be tossed
around if not anchored. Seek shelter indoors.

&&

LAT...LON 3494 8108 3482 8146 3482 8148 3478 8159
      3494 8170 3517 8138 3515 8114
TIME...MOT...LOC 0138Z 241DEG 41KT 3491 8156

HG

Special Weather Statement
National Weather Service Greenville-Spartanburg SC
951 PM EDT MON AUG 7 2017

GAZ018-026-028-SCZ001-002-004-005-010-080215-
Hart GA-Franklin GA-Stephens GA-Pickens Mountains SC-
Greater Pickens SC-Greater Oconee SC-Anderson SC-Oconee Mountains SC-
951 PM EDT MON AUG 7 2017

...STRONG THUNDERSTORMS WILL IMPACT CENTRAL FRANKLIN...SOUTHEASTERN
STEPHENS...NORTHERN HART...NORTHWESTERN ANDERSON...WESTERN PICKENS
AND OCONEE COUNTIES UNTIL 1015 PM EDT...

At 951 PM EDT, Doppler radar indicated strong thunderstorms along a
line extending from 4 miles northwest of Walhalla to 11 miles
southwest of Seneca to near Carnesville, and moving east at 35 mph.

Locations to be impacted include...
Clemson, Seneca, Hartwell, Walhalla, Carnesville, Central, Pendleton,
Westminster, Reed Creek and Lavonia.

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

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Gusty winds can blow down trees that are dead, or that have weakened
root systems. Outdoor furniture and similar items can be tossed
around if not anchored. Seek shelter indoors.

&&

LAT...LON 3429 8336 3456 8317 3486 8319 3502 8278
      3467 8270 3436 8288 3428 8336
TIME...MOT...LOC 0151Z 252DEG 31KT 3482 8312 3458 8310 3437 8326

HG

Special Weather Statement
National Weather Service Greenville-Spartanburg SC
1007 PM EDT MON AUG 7 2017

SCZ009-014-080230-
York SC-Chester SC-
1007 PM EDT MON AUG 7 2017

...STRONG THUNDERSTORMS WILL IMPACT CHESTER AND SOUTHEASTERN YORK
COUNTIES UNTIL 1030 PM EDT...

At 1006 PM EDT, Doppler radar indicated strong thunderstorms along a
line extending from 4 miles southeast of York to 8 miles northeast of
Chester to 15 miles northwest of Winnsboro, and moving northeast at
35 mph.

Locations to be impacted include...
Rock Hill, Chester, Fort Mill, Newport, Lesslie, Fort Lawn, Richburg,
Chester State Park, Catawba and Blackstock.

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

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Gusty winds can blow down trees that are dead, or that have weakened
root systems. Outdoor furniture and similar items can be tossed
around if not anchored. Seek shelter indoors.

&&

LAT...LON 3464 8090 3460 8089 3455 8105 3457 8130
      3477 8119 3495 8122 3506 8090 3501 8091
      3499 8089 3492 8086 3490 8088 3484 8087
      3483 8090 3479 8088 3475 8088 3470 8086
TIME...MOT...LOC 0206Z 245DEG 28KT 3495 8118 3480 8113 3457 8125

HG

Special Weather Statement
National Weather Service Greenville-Spartanburg SC
1021 PM EDT MON AUG 7 2017

SCZ002-004-005-010-080245-
Pickens Mountains SC-Greater Pickens SC-Greater Oconee SC-
Anderson SC-
1021 PM EDT MON AUG 7 2017

...STRONG THUNDERSTORMS WILL IMPACT ANDERSON...PICKENS AND
SOUTHEASTERN OCONEE COUNTIES UNTIL 1045 PM EDT...

At 1021 PM EDT, Doppler radar indicated strong thunderstorms along a
line extending from 10 miles west of Pickens to 3 miles north of
Clemson to 10 miles northwest of Anderson to 5 miles north of
Hartwell, and moving east at 25 mph.

Locations to be impacted include...
Anderson, Easley, Clemson, Seneca, Pickens, Homeland Park,
Powdersville, Piedmont, Belton and Central.

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

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Gusty winds can blow down trees that are dead, or that have weakened
root systems. Outdoor furniture and similar items can be tossed
around if not anchored. Seek shelter indoors.

&&

LAT...LON 3435 8281 3437 8284 3444 8286 3448 8288
      3449 8291 3447 8301 3449 8304 3460 8300
      3472 8302 3481 8290 3493 8290 3500 8258
      3478 8245 3466 8247 3459 8242 3434 8266
TIME...MOT...LOC 0221Z 266DEG 23KT 3486 8290 3473 8282 3460 8280 3444
8295

HG