Special Weather Statement, NWS Greenville-Spartanburg, SC

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
455 PM EDT Sun Apr 23 2017

.SYNOPSIS...
A deep and vigorous low pressure system moves across Georgia to
the Carolina coast creating a lengthy period of moderate to heavy
rainfall and below-normal temperatures that persists through
Monday. Storm total rainfall accumulations of 2 to 5 inches are
likely. A drying and warming trend begins Tuesday and continues
through next weekend. A slight chance of diurnal mountain showers
and thunderstorms returns Thursday and persists through the weekend.

&&

.NEAR TERM /THROUGH MONDAY/...
As of 445 PM EDT Sunday: The current forecast remains on track with
only very minor adjustments needed to PoP for current radar
placement of returns and to add slightly to sky cover. Concern
continues to grow for possibly excessive rainfall rates developing
later this evening as the deeper forcing arrives and precipitable
water values surge to +2 to +3 standard deviations. The current
Flood Watch remains well placed.

Otherwise, a closed upper low moving through the mid South into the
TN valley late this afternoon continues to drive deep/moist swly
flow aloft across northeast GA and the western Carolinas.  At the
surface, high pressure anchored to the northeast continues to
promote CAD in the lee of the Appalachians, while a cold front moves
through the deep south ahead of the aforementioned upper low.  The
wedge front remains generally along/near the I20 corridor, however
is expected to lift slightly to the north overnight potentially
reaching into the I85 corridor late tonight, into mid morning,
favoring elevated convection amidst non-zero MUCAPE.  With that,
guidance favors quite a bit of additional precipitation across the
region, with the heaviest rainfall amounts oriented along the I77
corridor.  The fcst will feature widespread categorical pops
through the period, with QPF totals across northeast GA and the
extreme western Carolinas reaching upward of 1-2 inches, increasing
to the east into the I-77 corridor where totals could top out in the
3-4 inch range through the period.  Please refer to the latest
CAEFFAGSP for additional details.  River levels will certainly rise
across the region, especially in/near the Catawba basin where the
highest QPF totals are favored.  Conditions will slowly improve
during the day on Monday from the west as the entire system slides
east. However, expect little improvement across the NC/SC Piedmont
through the period.  With that, pops will taper from the west,
however remaining in the likely/categorical range generally east of
I-26.

&&

.SHORT TERM /MONDAY NIGHT THROUGH WEDNESDAY/...
As of 205 PM Sunday: Obviously the main short term concern will be
timing the ending of the precip potential, especially across the
eastern part of the forecast area, as upper low continues to wobble
in the vicinity of the SC Coast. This will place the I-77 corridor
in a good position to receive continued bands of rainfall associated
with the deformation zone north and west of the cyclone. In fact,
there's a decent consensus in deterministic guidance that another
.5-1 inch of rain will fall in this area Monday evening, and we will
forecast as much. This amount of qpf would certainly warrant an
extension of the Flood Watch, but that decision can be left to later
shifts and further collaboration with WFOs to our east and south.

Pops gradually taper off after midnight through Tuesday, really not
dropping below 20 percent until Tue afternoon, in line with
uncertainty regarding how quickly the upper low's influence will end
for our area. Temps will also be a bit problematic on Tuesday, as
areas along the Upper Savannah River Valley will likely see clearing
skies by afternoon, while locations along the I-77 corridor should
underneath a cloud shield. Tuesday's high temp forecast therefore
ranges from around 80 across the USRV to mid/upper 60s across the
northwest NC Piedmont.

The remainder of the short term will be decidedly tame, as upper
ridging builds along the Eastern Seaboard in the wake of the upper
low, and downstream of large scale central Conus height falls. This
will result in a return of much-welcomed dry conditions while Wed
max temps are expected to return to the 80s in most locations east
of the mtns.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/...
As of 215 PM Sunday: The medium range will see the establishment of
a massive/broad upper trough encompassing much of the western 2/3 of
the Conus, with ridging expected to dominate much of the East Coast.
This will result in unseasonably warm temperatures continuing across
our area through at least the end of the weekend.

The first in a series of short waves ejecting from the western Conus
trough will ride along the western periphery of the Eastern ridge
Wed night through Thursday, passing well west and north of our area.
Nevertheless, a weakening/occluding cold front is forecast top
approach the southern Appalachians and vicinity by the end of
Thursday. There will be a deep fetch of Gulf of Mexico moisture
immediately ahead of this feature, resulting in a decent amount of
pre-frontal instability. Despite the weakening forcing, this should
provide decent chances for convection, mainly across our western
areas Thu afternoon/evening. Shear is forecast to be adequate (but
not much more than that) for organized convection, so the severe
threat will depend substantially on the amount of buoyancy that is
realized, and this is still quite uncertain.

Warm sector air mass remains pretty much ensconced across the area
late in the week through the weekend, with global model guidance
depicting a summer-like pattern, with anomalously strong Bermuda
high supporting plenty of heat/moisture/instability each afternoon.
Diurnal deep convective chances (mainly in the 20-40% range) will
therefore be advertised each day from Fri through the weekend.

&&

.AVIATION /21Z SUNDAY THROUGH FRIDAY/...
At KCLT and Elsewhere: Vast IFR/LIFR restrictions expected through
this period as a CAD wedge remains draped atop the region.
Meanwhile, a slow moving upper low continues to slide east across
the MS/TN valleys, moving through the fcst area overnight into
Monday.  With that, ample upglide as well as upper divergence will
yield increasing precipitation coverage through the evening after
the current brief lull ends. Steepening mid level lapse rates atop
the wedge in association with the approaching upper low will lead to
at least a non-zero chance for TS, however think probs are too low
to include at this time. Overall, expect multiple round of
shra/+shra tonight/overnight with variable vsby/cigs, both in the
IFR/LIFR range.  Nely winds will remain quite elevated beneath the
wedge due to a barrier jet, thus did keep such in at all sites
through the period.

Outlook: An area of low pressure will cross the southern CWFA thru
Monday while strong sfc ridging builds in from the north. Widespread
low clouds and precipitation are expected to persist thru this time.
Conditions should gradually improve Tuesday thru Wednesday morning
as dry air works in behind the departing low.

Confidence Table...

            21-03z        03-09Z        09-15Z        15-18Z
KCLT       Low   46%     High  89%     Med   66%     High  93%
KGSP       Med   61%     High  89%     Low   55%     Med   77%
KAVL       Med   77%     High  88%     High  81%     High  81%
KHKY       High  85%     High  85%     Med   62%     High  82%
KGMU       Low   50%     High  83%     Med   66%     Med   73%
KAND       High  94%     Med   66%     Med   66%     Med   69%

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

&&

.HYDROLOGY...
No changes to the current Flood Watch are presently expected. None
of the river forecast points are forecast to go into flood
currently, but locations along the Catawba river chain will need
very close monitoring through Monday as the heavy rain axis could
pivot over the area.

&&

.GSP WATCHES/WARNINGS/ADVISORIES...
GA...None.
NC...Flood Watch through Monday evening for NCZ033-035>037-048>053-
     056>059-062>065-068>072-082-501>510.
SC...Flood Watch through Monday evening for SCZ007>009-012>014.

&&

SYNOPSIS...JMP
NEAR TERM...CDG/HG
SHORT TERM...JDL
LONG TERM...JDL
AVIATION...CDG/HG
HYDROLOGY...HG

Hazardous Weather Outlook
National Weather Service Greenville-Spartanburg SC
221 PM EDT Sun Apr 23 2017

NCZ033-035>037-048>053-056>059-062>065-068>072-082-501>510-
SCZ007>009-012>014-241830-
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-
Spartanburg-Cherokee-York-Laurens-Chester-
221 PM EDT Sun Apr 23 2017

...FLOOD WATCH IN EFFECT THROUGH MONDAY EVENING...

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

   Flood Watch.

Widespread showers will continue across the area with periods of
heavy rain possible, especially tonight. Rainfall totals of up 3 to 4
inches are possible which could lead to flooding. In addition, a few
thunderstorms are possible this afternoon south of the I-85
corridor. Although cloud to ground lightning and heavy rain will be
the main threats, an isolated damaging wind gust cannot be ruled out.

.DAYS TWO THROUGH SEVEN...Monday through Saturday.

..Monday...Heavy rain with flooding possible. Showers taper off
through the day Monday. However, any flooding that does develop
could linger through the morning.
..Tuesday...No hazardous weather is expected at this time.
..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.

.SPOTTER INFORMATION STATEMENT...

Skywarn spotters are requested to forward any reports of flooding to
our office.

GAZ010-017-018-026-028-029-SCZ001>006-010-011-019-241830-
Rabun-Habersham-Stephens-Franklin-Hart-Elbert-Oconee Mountains-
Pickens Mountains-Greenville Mountains-Greater Oconee-
Greater Pickens-Greater Greenville-Anderson-Abbeville-Greenwood-
221 PM EDT Sun Apr 23 2017

This Hazardous Weather Outlook is for northeast Georgia and upstate
South Carolina.

.DAY ONE...This Afternoon and Tonight.

Widespread showers will continue across the area with periods of
heavy rain possible, especially tonight. Rainfall totals of up to 3
inches are possible which could lead to flooding. In addition, a few
thunderstorms are possible this afternoon south of the I-85
corridor. Although cloud to ground lightning and heavy rain will be
the main threats, an isolated damaging wind gust cannot be ruled out.

.DAYS TWO THROUGH SEVEN...Monday through Saturday.

..Monday...Heavy rain with flooding possible. Showers taper off
through the day Monday. However, any flooding that does develop
could linger through the morning.
..Tuesday...No hazardous weather is expected at this time.
..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.

.SPOTTER INFORMATION STATEMENT...

Skywarn spotters are requested to forward any reports of flooding to
our office.

CDG

Special Weather Statement
National Weather Service Greenville-Spartanburg SC
447 PM EDT SUN APR 23 2017

SCZ009-014-232145-
York SC-Chester SC-
447 PM EDT SUN APR 23 2017

...A STRONG THUNDERSTORM WILL IMPACT WESTERN CHESTER AND SOUTH
CENTRAL YORK COUNTIES UNTIL 545 PM EDT...

At 446 PM EDT, Doppler radar was tracking a strong thunderstorm 5
miles west of Chester, or 4 miles northwest of Chester State Park,
moving northeast at 25 mph.

Locations to be impacted include...
Chester, Mcconnells, Lowrys, Chester State Park, Leeds and Edgemoor.

Wind gusts up to 40 mph and pea size hail will be possible in these
areas.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

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 3468 8146 3469 8145 3499 8128 3485 8098
      3458 8129
TIME...MOT...LOC 2046Z 216DEG 24KT 3471 8132

STUREY

Special Weather Statement
National Weather Service Greenville-Spartanburg SC
513 PM EDT SUN APR 23 2017

GAZ010-017-018-026-028-029-NCZ062>064-SCZ001-004-232215-
Elbert GA-Hart GA-Franklin GA-Rabun GA-Stephens GA-Habersham GA-
Transylvania NC-Southern Jackson NC-Macon NC-Greater Oconee SC-
Oconee Mountains SC-
513 PM EDT SUN APR 23 2017

At 511 PM EDT, Doppler radar indicated heavy rain showers along a
line extending from 8 miles north of Clayton to near Clarkesville to
6 miles north of Athens, and moving northeast at 20 mph.

Rainfall between one quarter of an inch and three quarters of an
inch will be possible in about an hour, as well as a rumble or two
of thunder.

Locations to be impacted include...
Toccoa, Walhalla, Clayton, Clarkesville, Carnesville, Hartwell,
Cornelia, Baldwin, Royston and Westminster.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

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 3417 8310 3423 8308 3427 8312 3424 8317
      3426 8330 3423 8335 3426 8334 3433 8339
      3446 8340 3449 8353 3448 8357 3459 8359
      3503 8343 3531 8286 3483 8304 3450 8297
      3448 8299 3448 8297 3411 8289 3408 8301
TIME...MOT...LOC 2111Z 242DEG 19KT 3500 8337 3463 8351 3405 8338

STUREY