Special Weather Statement, NWS Greenville-Spartanburg, SC

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
242 PM EDT Wed Jul 5 2017

.SYNOPSIS...
Broad high pressure will remain centered over the western Atlantic
while a slow moving, weak frontal zone lingers over the region
into Thursday. Scattered showers and thunderstorms is expected
each day. A second front will push through the area this weekend
with somewhat drier and cooler air briefly settling in behind it.

&&

.NEAR TERM /THROUGH THURSDAY/...
As of 245 PM EDT: Showers and thunderstorms were developing around
the region, mainly closer to the mtns/foothills, in a moderately
unstable  environment characterized by sbCAPE on the order of
2500-3500 J/kg. As expected, dCAPE looks better than yesterday
with a larger area of greater than 800 J/kg. Have made some tweaks
to the precip chances based on upstream radar trends. The least
chance still seems to be over the Lakelands, but that could change
depending on outflow boundaries.

As long as the axis of a positively tilted upper trof remains
to our west, keeping the wrn Carolinas in a WSW flow aloft with
plenty of low level moisture in place, expect our weather to be
persistent over the next 24 hours. That means more showers and
storms lingering into the late evening hours with more activity
upstream closer to the trof axis, which would drift in from the
west over the mtns toward daybreak. On Thursday, new convection
would break out across the mtns during midday, or perhaps
closer to outflows or cloudy/clear boundaries. We could see some
extra enhancement to convective potential in the afternoon as a
better upper wave moves in from the west with the main trof axis
approaching slowly. The models suggest the best chances over the
NC mtns, and that seems reasonable, but suspect as in the last
few days, the better instability to the S will be fuel enough for
better coverage than indicated in the guidance across northeast
GA and upstate SC. Cannot rule out a few more severe storms, with
damaging wind the main threat, given mid-level dry air and decent
dCAPE once again. Temps will continue to run a bit above normal.

&&

.SHORT TERM /THURSDAY NIGHT THROUGH SATURDAY/...
As of 230 PM EDT Wednesday:  Complicated portion in this part of the
forecast cycle. There should be an ongoing slug of showers and
thunderstorms early Thursday evening and mainly in the mountains of
western North Carolina. Elsewhere chance or slight chance in the
evening. The precipitation will be tied into weak surface
convergence, the end of the diural heating cycle, and upslope flow
in the mountains.

We will then draw back on the POPS, except maintaining middle of the
road chance POPS in the mountains, with the approach of an upper
level trough and pre-frontal wind shift. We brought back some token
small chance values elsehwhere.

The Friday and Saturday portion of the forecast remains iffy! There
still in not a large QPF response from the NAM and GFS, although
they have had an uptick in precipitation. The older European model
and latest Canadian model were a tad more robust for the
precipitation potential Friday. Considering we should still be moist
and unstable, with heights falling and lapse rates steepening, plus
preliminary wind shift line and channelled voriticy, all lead to a
continuation of precipitation potential. We have tapered POPS down
by evening with the idea that the initial primary forcing will have
passed.

Once again late Friday night we go back to the mountains of western
North Carolina for an uptick in showers and thunderstorms, with a
secondary wind shift dropping into the area. We then carry chance
POPS into Saturday across the remainder of the forecast area (FA).
Perhaps once all the models reach more of a consensus, POPS will go
up across the board on Friday.

Our thermal pattern does not show a great deal of change, although a
bit lower on Saturday. We will follow the trends as they appear to
fit the idea of the ongoing forecast.

&&

.LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/...
As of 155 PM Wed: This period begins Saturday evening with the 500mb
trough over the East with axis along or near the Appalachians. The
surface cold front pushes south of I-85 and becomes stationary from
Alabama to GA near Savannah.  As weak high pressure predominates
north of the front Sunday and Monday, slightly drier air will keep
convection at a minimum. Heights will slowly rise Monday and Tuesday
and a few models are showing the stationary front lifting north.
Although timing is different among the models, they are showing
another cold front crossing the Great Lakes Monday night or Tuesday.
This will focus more convection over our region in mid week as weak
high pressure loses its influence. The GFS is most progressive in
taking the front all the way to the Carolinas Wednesday night. By
Wed night on the EC, the front would still be from near Memphis to
Indiana.  Toward the end of the week, the upper ridge remains over
the four corners area while models show the trough reasserts itself
over the East.

Max Temps will be a couple degrees below normal and Min Temps near
or slightly above normal.

&&

.AVIATION /19Z WEDNESDAY THROUGH MONDAY/...
At KCLT: VFR for the time being, but a small potential
for a temporary MVFR ceiling for the first hour or
two. Convection-allowing models not as keen on developing precip
across the CLT metro area later today as they were yesterday,
but prefer to keep a TEMPO in the fcst rather than just a VCTS as
a slim majority favors a round of thunderstorms beginning approx
21Z. This could be a bit too early depending on the movement of
the numerous storms upstream over ern TN/nw GA. Wind should stay
light SW. Will keep a vicinity shower for a few hours afterward
into the late evening, thereafter just mid/high level convective
debris and a light SW wind. Could see another round of low stratus
around daybreak if we get the precip today, but chances are too
low to mention. The SW flow looks a bit stronger on Thursday.

Elsewhere: Similar conditions to KCLT. Confidence high enough
to include TSRA at KAVL, but not the other sites where a
VCTS is kept. Will monitor convective trends and amend TAFs
accordingly. KAVL and KHKY have the best chance of seeing any
restrictions overnight.

Outlook: Moist and unsettled weather will continue through
the late week. Thunderstorms may become more numerous Thursday
afternoon into Friday as an upper wave passes followed by a cold
front. Nocturnal restrictions can be expected in any locations
receiving heavy rainfall, and also in the mountain valleys. Some
drying is indicated this weekend.

Confidence Table...

            18-24Z        00-06Z        06-12Z        12-18Z
KCLT       High 100%     High 100%     High  91%     High 100%
KGSP       High 100%     High 100%     High 100%     High 100%
KAVL       High 100%     High 100%     High 100%     High 100%
KHKY       High 100%     High 100%     High 100%     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...PM
SHORT TERM...TS
LONG TERM...DEO
AVIATION...PM

Hazardous Weather Outlook
National Weather Service Greenville-Spartanburg SC
640 AM EDT Wed Jul 5 2017

GAZ010-017-018-026-028-029-NCZ033-035>037-048>053-056>059-062>065-
068>072-082-501>510-SCZ001>014-019-061045-
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-
640 AM EDT Wed Jul 5 2017

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

.DAY ONE...Today and Tonight.

Scattered thunderstorms are expected to develop this afternoon.
Dangerous cloud-to-ground lightning is possible with any of these
storms. However, conditions will be favorable for a few of them to
produce brief damaging winds.

.DAYS TWO THROUGH SEVEN...Thursday through Tuesday.

..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.
..Monday...No hazardous weather is expected at this time.
..Tuesday...No hazardous weather is expected at this time.

.SPOTTER INFORMATION STATEMENT...

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

Wimberley

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