Special Weather Statement, NWS Greenville-Spartanburg, SC

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
1038 PM EDT Thu May 4 2017

.SYNOPSIS...
A deep low pressure system will move across Tennessee from west to
east tonight and Friday with abundant moisture over our area tonight
ahead of the system. This low pressure system moves north of our
region this weekend with high pressure becoming our dominant weather
feature through mid week. The next low pressure system reaches our
region late next week.

&&

.NEAR TERM /THROUGH FRIDAY NIGHT/...
As of 1015 PM Thursday: sustained winds have been coming down over
the past few hours, thus it was decided to go ahead and cancel the
wind advisory for all zones. Numerous showers and thunderstorms
continue to stream across the fcst area from the south. We've been
seeing some mid to low lvl rotation in some of the cells, however
it has not been able to tighten and translate to the ground yet.
We're also observing some pretty heavy rain rates in the stronger
cells, but they're moving at a fast clip. Any additional training over
redundant areas could produce flash flooding. Shear and helicity
remain very high, but lapse rates are mediocre. In addition, model
soundings still indicate that by roughly 07z a mid-lvl inversion
will develop over our western zones and the eastern zones by about
12z which should help suppress any remaining convection.

Otherwise, the upper low will slowly drift over the fcst area during
the next 24 to 36hrs but is not expected to lift north of the region
until early next week. At the sfc, the warm front will lift north of
the CWFA early Fri morning as the cold front approaches and moves
across the fcst area later in the day. By the end of the near-term
period early Sat, the center of the low will have lifted well to our
north, yet moist return flow on its back side will keep POPs up over
our area. Temps will remain well below normal on Friday with cooler
air spreading over the region behind the front and abundant cloud cover
persisting across the CWFA.

&&

.SHORT TERM /SATURDAY THROUGH SUNDAY/...
As of 200 PM EDT Thursday: The short term begins at 00z Saturday
with the deep upper closed low in place over the Southern
Appalachians. Moisture associated with the upper low will remain
generally over the mountains overnight, with temperatures
plummeting into the 30s and lower 40s across the mountains (mid to
upper 40s Piedmont), possibly reaching that critical freezing level
at the very highest elevations. Some light snow certainly not out of
the question - again we're mainly talking Mt. Mitchell and other
high peaks, but some flurries certainly possible across the Smokies
and Balsams. For now, not too concerned about frost potential in the
valleys with winds remaining a too high with strong surface gradient
in place, but will have to monitor.

Moisture should spread across the foothills into the Piedmont during
the day on Saturday. Lapse rates will steepen as the upper low and
associated mid-level CAA moves across, and even though surface
temperatures in the wake of the cold front will struggle to get to
70, there should be enough instability to result in at least
isolated thunderstorms, with best chances across the NC mountains
and foothills (can't rule it out over the Piedmont though). With
such steep lapse rates in place and much cooler temperatures aloft,
some small hail will certainly be possible. The surface gradient
will tighten somewhat during the day and with mixing stronger winds
down, should be a breezy day, though still below thresholds for wind
advisory.

The upper low rotates northeast as a shortwave dives down the
western periphery of the trough, pushing into the mountains Saturday
night. Another round of very light snow showers certainly possible
at those highest elevations, but storm total (Fri and Sat nights)
we're looking at a whopping half inch or so at Mt. Mitchell...but
still a bit of a novelty nonetheless. The gradient remains strong so
again frost concerns are minimal, but generally expecting another
cool night (5-8 degrees below seasonal normal) across the area. Some
indications that moisture associated with this secondary shortwave
may break containment, especially with the GFS and NAM (not so much
the ECMWF), and so have increased pops across southern zones early
Sunday to account for this.

Pops drop off drastically after sunrise Sunday, and despite full
sunshine, continued strong CAA especially in the wake of the
secondary shortwave will keep temperatures a good 8-10 degrees below
seasonal normals on Sunday. Should still be a bit of a breeze,
though not as strong as on Saturday.

&&

.LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/...
As of 230 PM EDT Thursday: High-amplitude omega blocking pattern in
place with deep troughing over the Eastern Seaboard, ridging over
the Plains, and another deep cutoff upper low over southern
California to start the extended. The wavetrain will slowly slide
east, but with northwest flow aloft and cool high pressure building
in, we should see a couple of days of below-normal temperatures for
the beginning of the work week, though with a slow warming trend.

Guidance wants to bring a channeled vort max down the northwest flow
aloft with some attendant moisture Tuesday night into Wednesday, and
both deterministic GFS and ECWMF are inducing surface low formation
off the coast around mid-week. This wouldn't affect us, but
interesting to see nonetheless. The eastern upper low continues to
rotate over New England and the northern Mid-Atlantic states while
the southwest low lifts into the southern Rockies and into the
Plains late in the work week. Definitely some uncertainty with the
progression of this system but looks like some sort of elongated
front stretching between the two surface systems will be hovering
over the area, with slight to low-chance pops returning early
Wednesday and lingering through the end of the period, with some
oscillation due to uncertainty in the front. Should see temperatures
return to near- to slightly above-average by the end of the period.

&&

.AVIATION /03Z FRIDAY THROUGH TUESDAY/...
At KCLT and elsewhere: cig and visby restrictions are expected to
persist thru the 00z taf period over all sites. Showers and TS will
continue thru the evening and into the overnight as the center of
the low moves closer to the fcst area and the associated warm front
lifts farther north across the CWFA. We are finally starting to see
some lightning from some of the taller cells and this trend should
continue into the overnight. POPs will eventually taper off by the
late morning with some slight to solid chance remaining over all
sites except KAVL which will have high-end chance to low-end likely
thru the rest of the taf period. Winds will remain SELY into the
overnight and then veer around to SLY and then SWLY by late morning.
Speeds will remain brisk in the 9 to 15kt range for the period with
intermittent gusts in the 18 to 22kt range.

Outlook: Isolated to scattered showers and thunderstorms will linger
across the area into Saturday as a large area of low pressure slowly
lifts north of the region. Drying expected for Sunday and early next
week.

Confidence Table...

            02-08Z        08-14Z        14-20Z        20-00Z
KCLT       High  85%     High  92%     High  91%     High 100%
KGSP       High  95%     High  85%     High  92%     High  83%
KAVL       High  93%     Med   63%     Med   78%     High  84%
KHKY       High  88%     Med   76%     High  82%     High  86%
KGMU       High  95%     High  88%     High  92%     High  86%
KAND       High  80%     Med   73%     High  85%     High  97%

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...DEO
NEAR TERM...JPT
SHORT TERM...TDP
LONG TERM...TDP
AVIATION...JPT

Hazardous Weather Outlook
National Weather Service Greenville-Spartanburg SC
1037 PM EDT Thu May 4 2017

GAZ010-017-018-026-028-029-NCZ033-035>037-048>053-056>059-062>065-
068>072-082-501>510-SCZ001>014-019-060245-
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-
1037 PM EDT Thu May 4 2017

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

.DAY ONE...Tonight.

Scattered thunderstorms are expected to continue late tonight and
through the overnight. The threat for damaging winds or a brief
tornado is low, but cannot be ruled out, especially east of I-26.
Locally heavy rainfall is also expected with flash flooding possible
where storms train behind each other.

.DAYS TWO THROUGH SEVEN...Friday through Wednesday.

..Friday...Lingering showers and thunderstorms are likely through the
early morning hours.
..Saturday...No hazardous weather is expected at this time.
..Sunday...No hazardous weather is expected at this time.
..Monday...No hazardous weather is expected at this time.
..Tuesday...No hazardous weather is expected at this time.
..Wednesday...No hazardous weather is expected at this time.

.SPOTTER INFORMATION STATEMENT...

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

JPT

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Special Weather Statement
National Weather Service Greenville-Spartanburg SC
1138 PM EDT THU MAY 4 2017

SCZ009-014-050415-
York SC-Chester SC-
1138 PM EDT THU MAY 4 2017

...A STRONG THUNDERSTORM WILL IMPACT WESTERN CHESTER AND SOUTHERN
YORK COUNTIES UNTIL 1215 AM EDT...

At 1138 PM EDT, Doppler radar was tracking a strong thunderstorm 6
miles west of Chester, or 5 miles west of Chester State Park, moving
north at 45 mph.

Locations to be impacted include...
Rock Hill, Chester, Sharon, Mcconnells, Lowrys, Chester State Park,
Newport, Leeds and Cornwell.

Wind gusts up to 40 mph and very heavy rainfall rates up to 2 inches
per hour 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.

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. Do not drive across
flooded roads.

&&

LAT...LON 3457 8142 3458 8143 3460 8142 3461 8142
      3496 8136 3499 8100 3482 8103 3456 8119
TIME...MOT...LOC 0338Z 198DEG 39KT 3468 8133

MOORE

Special Weather Statement
National Weather Service Greenville-Spartanburg SC
1201 AM EDT FRI MAY 5 2017

GAZ018-026-028-029-SCZ001-004-010-050445-
Elbert GA-Hart GA-Franklin GA-Stephens GA-Greater Oconee SC-
Anderson SC-Oconee Mountains SC-
1201 AM EDT FRI MAY 5 2017

...STRONG THUNDERSTORMS WILL IMPACT FRANKLIN...SOUTHEASTERN
STEPHENS...ELBERT...HART...SOUTHWESTERN ANDERSON AND SOUTHEASTERN
OCONEE COUNTIES UNTIL 1245 AM EDT...

At 1201 AM EDT, Doppler radar indicated strong thunderstorms along a
line extending from near Carnesville to 7 miles northeast of
Danielsville to 6 miles northeast of Lexington, and moving northeast
at 45 mph.

Locations to be impacted include...
Seneca, Elberton, Hartwell, Carnesville, Royston, Reed Creek,
Lavonia, Gumlog, Bowman and Canon.

Wind gusts up to 45 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.

&&

LAT...LON 3399 8283 3398 8286 3401 8291 3401 8294
      3403 8294 3410 8304 3415 8306 3417 8310
      3423 8308 3427 8311 3424 8317 3425 8322
      3437 8330 3484 8295 3464 8283 3463 8285
      3456 8278 3399 8272 3397 8276
TIME...MOT...LOC 0401Z 211DEG 39KT 3436 8322 3417 8311 3394 8305

MOORE

Special Weather Statement
National Weather Service Greenville-Spartanburg SC
1213 AM EDT FRI MAY 5 2017

SCZ008-009-013-014-050445-
York SC-Cherokee SC-Union SC-Chester SC-
1213 AM EDT FRI MAY 5 2017

...A HEAVY RAIN SHOWER WILL IMPACT NORTHWESTERN CHESTER...
SOUTHWESTERN YORK...SOUTHEASTERN CHEROKEE AND NORTHEASTERN UNION
COUNTIES UNTIL 1245 AM EDT...

At 1213 AM EDT, Doppler radar was tracking a heavy rain shower 6
miles southwest of Union, or near Rose Hill State Park, moving
northeast at 40 mph.

Locations to be impacted include...
Union, Monarch Mill, Buffalo, Lockhart, Saratt, Adamsburg and Bullock
Creek.

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

LAT...LON 3463 8166 3473 8171 3499 8146 3486 8128
TIME...MOT...LOC 0413Z 224DEG 35KT 3465 8170

LANE