Special Weather Statement, NWS Greenville-Spartanburg, SC

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
429 PM EDT Sat Jul 1 2017

.SYNOPSIS...
High pressure centered over the western Atlantic and a broad upper
level trough will continue over the eastern part of the nation into
the early part of the week.  A weak cold front lingers west to east
over our region Sunday into early week helping in the generation of
showers and storms. Another upper level disturbance will approach
our area later in the week enhancing the coverage of showers and
storms.

&&

.NEAR TERM /THROUGH SUNDAY/...
As of 420 PM EDT Saturday: Continuing to watch multiple rounds of
convection this afternoon, with the first being ongoing shra/tsra
along a diffuse sfc boundary across portions of the Upstate,
northward along I85 into CLT metro.  Said convection remains
rather robust thanks to ample heating and thus diurnally driven
cape upwards of 2-3k j/kg along and south of I85 per the SPC Meso.
With that, expecting further development over the next few hours
across the Upstate, with some strong/severe convection certainly
possible.  Meanwhile, another wave of convection continues to slide
east out of the TN Valley into portions of western NC and northeast
GA.  According to the SPC Meso, instability fields are much lower,
however still at levels supportive of deep convection with severe
storms not out of the question.  One additional threat regionwide
(however focused mainly across the western tier of the fcst area)
will be flash flooding as storm motions are rather weak, which
combined with robust rainfall and already decreased ffg values,
could result in isolated flooding concerns.  As for the fcst,
tweaked pops/t/td and sky to align with recent radar/obs/sat as
well as CAM guidance.

As of 2:10pm EDT Saturday:  Currently, some showers and
thunderstorms have fired only a weak surface boundary that
runs northeast to southwest along the foothills from Iredell to
Polk counties.  These storms are expected to move ENE through the
afternoon.  More storms are expected to enter western parts of the
CWA later this afternoon/evening as an upper level disturbance
moves eastward across the area.  An area of thunderstorms near
severe intensity currently exists in central Tennessee with this
wave, and these showers will continue eastward, reaching northeast
Georgia and western North Carolina by 6pm, with some earlier
showers popping up ahead of the main activity also possible.
There is some chance for severe outflows from any of these storms,
along with brief torrential rainfall and heavy lightning.

Clearing skies have allowed temperatures to warm to near or above
seasonal normals.  Moisture is still in place and this warming has
resulted in MLCAPE increasing to the highest levels seen this week
at 1500 to 2000 j/kg.  Shear is still weak, but with higher CAPE,
some strong outflows will be a risk this afternoon.

Following passage of shortwave, surface trough also moves eastward
and low-level winds veer to become more northwesterly.  This will
help to dry things a little bit with dewpoints on Sunday several
degrees below Saturday.  With reduced moisture, surface boundary
east of the area, and a lack of shortwave activity, POPs and
thunderstorm chances are much lower on Sunday. With less cloudy
and drier conditions on Sunday, highs will warm into the low 90s
in piedmont areas to mid 80s in the mountains.

&&

.SHORT TERM /SUNDAY NIGHT THROUGH TUESDAY/...
As of 230 PM EDT Saturday:  An interesting twist for this part of
the forecast cycle. It appears the suite of models are trying to
allow several short waves aloft, to zip across the southern edge of
the westerlies, and cross the Carolina's and northeast Georgia. This
would be from Monday into Tuesday.

These pockets of energy will interact with a moist and unstable
atmosphere, and potentially allow a couple episodes of greater
shower and thunderstorm coverage. Actually the NAM closes off an H7
and H85 center and drifts it through the region.

We will allow precipitation to wane Sunday night, but not shut off
completely. We will then follow the first short wave to enhance
showers and thunderstorms Monday into Monday night. Another downward
trend in POPS again late Monday night, as the energy moves
through, but not completely ending.

The second wave for Tuesday will increase shower and thunderstorm
coverage once again. Meanwhile throughout the two day period there
will be a surface convergence boundary, although weak, which could
focus the activity. However, at this time the small scale details
are rather nebulous.

Since we are forecasting more clouds and precipitation Monday and
Tuesday, we have lowered maximum temperatures a few degrees.
Otherwise continuity with the previous temperature forecast was
followed.

&&

.LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/...
As of 205 PM EDT Saturday: Starting Tuesday evening with the broad
upper trough over the East and ridge centered over the Four Corners.
The nearly closed off shortwave trough will be over Missouri Tuesday
evening and moving slowly toward our region.  The GFS has a well
defined low level circulation over the Upper Savannah River Valley
Tuesday night. The EC little low pressures over the Carolinas at
that time so looks a bit active to start this medium range.  The
Missouri shortwave crosses the Ohio Valley Wednesday with more
enhancement of convection for our region especially late Thursday.
CAPE values between 2500 and 3000 late Thursday with highest values
over NE GA and Upstate SC. Some shear will also help in generating
strong storms.  The models have a fairly deep trough over the East
Coast next weekend and a big ridge from the eastern Rockies north
into Canada.  The front that moves through Thursday night should
linger just south of our area through the weekend. So the scattered
convection hangs on.

Temperatures should remain near normal and maybe Max Temps just
below if the could cover is persistent.

&&

.AVIATION /21Z SATURDAY THROUGH THURSDAY/...
At KCLT and elsewhere: Currently some thunderstorms are firing along
a weak convergence boundary from north of KGSP to north of KCLT.
These showers will move ESE and increase in coverage through 0Z this
evening.  More showers and thunderstorms are expected to move into
the area after 21Z from the west associated with an upper level
disturbance.  These thunderstorms will be accompanied by divergent
outflows with highly variable and gusty winds.  Thunderstorms will
move east of the area and decline by midnight.  Some low clouds and
patchy fog are also possible Sunday morning, especially in
mountainous areas.  Overnight, surface winds will veer, becoming
more westerly to northwesterly as weak surface boundary moves out of
the area.  With somewhat dryer air, showers and clouds will be less
impactful on Sunday when conditions are expected to be VFR following
burn-off of any fog/low clouds.

Outlook: A moist and unsettled pattern will persist into early
next week, featuring mainly afternoon/evening SHRA/TSRA and areas
of nocturnal restrictions.

Confidence Table...

            20-02Z        02-08Z        08-14Z        14-18Z
KCLT       High 100%     Med   68%     High 100%     High 100%
KGSP       High 100%     High 100%     High 100%     High 100%
KAVL       High 100%     High 100%     High  83%     High 100%
KHKY       High 100%     High 100%     Med   75%     High 100%
KGMU       High 100%     High 100%     High 100%     High 100%
KAND       High 100%     High 100%     High 100%     High 100%

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...CDG/WJM
SHORT TERM...TS
LONG TERM...DEO
AVIATION...WJM

Hazardous Weather Outlook
National Weather Service Greenville-Spartanburg SC
532 PM EDT Sat Jul 1 2017

GAZ010-017-018-026-028-029-NCZ033-035>037-048>053-056>059-062>065-
068>072-082-501>510-SCZ001>014-019-021100-
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-
532 PM EDT Sat Jul 1 2017

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

.DAY ONE...Tonight.

A moist and unstable airmass persists across the region. Scattered to
numerous showers and thunderstorms will continue into the evening,
before gradually waning after dark. Until then some of the stronger
storms may produce damaging winds, large hail and torrential
rainfall. The torrential rain could generate local flooding issues.
Frequent and dangerous cloud to ground lightning strikes are likely.

.DAYS TWO THROUGH SEVEN...Sunday through Friday.

..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.
..Thursday...No hazardous weather is expected at this time.
..Friday...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

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