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
648 PM EDT MON AUG 7 2017

NCZ035-036-056-072315-
Iredell NC-Alexander NC-Catawba NC-
648 PM EDT MON AUG 7 2017

...A STRONG THUNDERSTORM WILL IMPACT CENTRAL CATAWBA...SOUTHERN
ALEXANDER AND WEST CENTRAL IREDELL COUNTIES UNTIL 715 PM EDT...

At 647 PM EDT, Doppler radar was tracking a strong thunderstorm near
Hickory, moving northeast at 25 mph.

Locations to be impacted include...
Hickory, Newton, Taylorsville, Statesville, St. Stephens, Conover,
Longview, Bethlehem, Stony Point and Claremont.

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 3598 8105 3574 8089 3561 8131 3573 8139
      3576 8137 3577 8135 3578 8136 3579 8135
      3580 8133 3582 8134
TIME...MOT...LOC 2247Z 241DEG 24KT 3573 8130

HG

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

NCZ056-068>070-072330-
Gaston NC-Cleveland NC-Lincoln NC-Catawba NC-
700 PM EDT MON AUG 7 2017

...STRONG THUNDERSTORMS WILL IMPACT SOUTHWESTERN CATAWBA...LINCOLN...
CENTRAL CLEVELAND AND NORTHWESTERN GASTON COUNTIES UNTIL 730 PM
EDT...

At 659 PM EDT, Doppler radar indicated strong thunderstorms along a
line extending from 15 miles east of Forest City to near Shelby to 12
miles northeast of Gaffney, and moving northeast at 40 mph.

Locations to be impacted include...
Shelby, Lincolnton, Gastonia, Kings Mountain, Cherryville, Bessemer
City, Dallas, Maiden, Ranlo and Belwood.

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.

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 3554 8112 3528 8111 3519 8152 3527 8156
      3541 8170 3546 8170 3556 8156 3557 8154
      3559 8152 3569 8138
TIME...MOT...LOC 2259Z 240DEG 34KT 3542 8162 3530 8150 3519 8149

HG

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

SCZ007-012-013-080100-
Laurens SC-Union SC-Spartanburg SC-
832 PM EDT MON AUG 7 2017

...A STRONG THUNDERSTORM WILL IMPACT CENTRAL LAURENS...SOUTHEASTERN
SPARTANBURG AND SOUTHWESTERN UNION COUNTIES UNTIL 900 PM EDT...

At 832 PM EDT, Doppler radar was tracking a strong thunderstorm near
Laurens, moving northeast at 30 mph.

Locations to be impacted include...
Laurens, Clinton, Rose Hill State Park, Mountville, Cross Keys, Cross
Anchor, Sedalia and Ora.

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 8199 3450 8211 3475 8177 3453 8158
      3452 8161 3453 8162 3452 8163 3453 8164
      3449 8168
TIME...MOT...LOC 0032Z 235DEG 24KT 3447 8198

HG