Special Weather Statement, NWS Greenville-Spartanburg, SC

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
239 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 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 /19Z MONDAY THROUGH SATURDAY/...
At KCLT and Elsewhere: a very moist air mass in place will make for
a challenging set of TAFs. Showers are developing quickly, as low
stratus is scattering out across the area. Instability will be great
enough for some of these showers to develop into tstms from mid-aftn
thru the evening. Timing the best coverage is difficult, however, as
better forcing will come from the west, not in line with the best
instability. For KCLT, will time prevailing SHRA from 00-06z. Will
mention TSRA at the other sites, where instability and coverage is
expected to be greater. The overnight, a cold front will push in
from the north by daybreak Tuesday. A wind shift from SW to NE will
probably be in the 12-15z time frame at KCLT and the Upstate TAF
sites. There should be plenty of VFR-level cloud cover to limit fog
and low stratus. However, given the very moist air mass and
weakening winds near the front, there will likely be some
restrictions around. Most of the guidance actually develops more
widespread MVFR to possibly IFR CIGS just behind the front across
the piedmont after 12z (earlier at KAVL and KHKY). Guidance also
depicts another round of showers entering the mountains after about
06z, then entering the piedmont after 12z.

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...

            18-24Z        00-06Z        06-12Z        12-18Z
KCLT       Med   70%     Low   55%     Med   68%     Med   70%
KGSP       High  94%     High 100%     High  84%     High  85%
KAVL       High 100%     High  95%     Low   57%     Med   78%
KHKY       High  95%     Med   79%     Low   57%     Med   73%
KGMU       High  93%     High 100%     High  99%     High  81%
KAND       High 100%     High  99%     Med   74%     Med   67%

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
SHORT TERM...TS
LONG TERM...JPT
AVIATION...ARK

Hazardous Weather Outlook
National Weather Service Greenville-Spartanburg SC
421 AM 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>014-019-080830-
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-
421 AM 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...Today and Tonight.

Numerous showers and thunderstorms will move across the area through
the day and into the evening. 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.

.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...

None.

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

SCZ002-003-005-006-072115-
Pickens Mountains SC-Greater Pickens SC-Greenville Mountains SC-
Greater Greenville SC-
446 PM EDT MON AUG 7 2017

...A STRONG THUNDERSTORM WILL IMPACT WESTERN GREENVILLE AND CENTRAL
PICKENS COUNTIES UNTIL 515 PM EDT...

At 446 PM EDT, Doppler radar was tracking a strong thunderstorm 4
miles west of Pickens, moving east at 40 mph.

Locations to be impacted include...
Greenville Downtown, Easley, Pickens, Greenville Eastside, West
Greenville, Berea, Welcome, Travelers Rest, Liberty and
Slater-Marietta.

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 3476 8284 3493 8289 3509 8237 3483 8229
      3481 8248 3482 8248 3482 8249 3480 8252
TIME...MOT...LOC 2046Z 255DEG 34KT 3487 8278

HG