Area Forecast Discussion
Issued by NWS Greer, SC

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000
FXUS62 KGSP 231515
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
1115 AM EDT Fri Jun 23 2017

.SYNOPSIS...
Shower and thunderstorm coverage associated with the remnants of
Cindy and an approaching cold front will increase from the west
tonight into early Saturday morning. Light showers will linger
Saturday morning as the front slowly crosses the area, and
thunderstorms may redevelop just ahead of the cold front over the
piedmont. Unseasonably cool and dry conditions will spread over the
forecast area in the wake of the front and persist through the
middle of next week.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 1105 AM EDT: Mostly good insolation and a warm start for much
of the area will require about a one degree increase in max temps
this afternoon, but developing clouds in heating with good boundary
layer moisture could inhibit insolation at times.

Otherwise, the remnant circulation of Cindy was moving into far
western TN late this morning, with associated tropical moisture
filling in east of the MS River and across central and western TN.
The Cindy remnants will continue to get slowly absorbed by the broad
longwave trough in place over the northern tier of the country. The
upper ridge over the southeast will slowly flatten and be pushed
south as the phased trough pushes into the Appalachians tonight. We
could see some diurnally-driven scattered convection across the
mountains, but then a non-diurnal rampup of convection should start
this evening. The increasing surface pressure gradient as the
remnant Cindy surface circulation approaches should lead to breezy
south/southeast winds which may provide at least some relief from
the humidity.

As we move through this evening and the front approaches, convection
should begin with some upslope showers in the southwest mountains,
with a potential convective line moving into western zones sometime
after 00z. Surface-based instability will be limited, but should
still see CAPEs slowly increase to between 500-750ish J/kg ahead of
the front. Deep-layer shear will move in as well with a 50+kt 850mb
LLJ ahead of Cindy`s absorbed remnants, with resulting 0-6km bulk
shear generally 30-40kt, but could creep up toward 50kt. So with
this, despite the overall lack of widespread instability, cannot
rule out isolated severe convection, and as with any tropical
remnants, mini supercells and perhaps a brief tornado cannot be
ruled out. SPC`s Marginal Risk looks to cover this well, but the
problem is that anything that does occur would be nocturnal.

Other concern is rainfall, but it really looks like the mountains
will break up quite a bit of the widespread heavy rain. Day 1 QPF
isn`t all that impressive, with around 1.5" in extreme western
Graham County (highest in the CWA)...and though 1hr FFG is 1-3",
that 1.5" in 24h was enough to warrant a Slight Risk of excessive
rain. For now, it just doesn`t seem like enough concern of for a
Flash Flood Watch. No doubt training convective cells may lead to an
isolated threat especially in the mountains, and with soils fairly
wet (especially after this morning`s rain) it probably wouldn`t take
much. But just not enough confidence for a Watch at this time.

&&

.SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/...
As of 305 AM EDT Friday: the short-term fcst picks up at 12z on
Saturday with longwave upper trofing digging down across the Great
Lakes and steep upper ridging over the West and East Coasts. The
upper lvl pattern is not expected to change much thru the period
with the trof axis remaining just to our NW and the ridge amplifying
to our west. At the sfc, a robust-looking cold front will be moving
thru the CWFA by early Sat, with widespread showers and thunderstorms
likely as it does. The models are hesitant to move the front south
of the CWFA on Saturday and keep the bndy just to our southeast thru
Sunday. By the end of the period early Monday, strengthening Canadian
high pressure to our NW finally pushes the bndy offshore. Precipitation
chances will steadily diminish Sat night thru early Sun with the rest
of Sunday expected to be dry and a bit cooler.

&&

.LONG TERM /MONDAY THROUGH THURSDAY/...
As of 255 AM EDT Friday: the extended fcst picks up at 12z on Monday
with a broad longwave upper trough centered over the Great Lakes to
our NW. A reinforcing upper shortwave digs southward on the backside
of the trof and moves over the fcst area on Tuesday. As the shortwave
lifts NE, heights begin to rebound as upper ridging begins to build
to our south. At the sfc, cooler and drier should be in place over
the CWFA by early Monday with broad high pressure centered to our NW
and a frontal bndy to our SE. Over the next few days, the high will
slide SE and over the fcst and eventually move off the Atlantic Coast
by the end of the period late Thursday/early Friday. As for the sensible
wx, the period should be mostly dry with only some slight chance PoPs
towards the end of the period when we get back under more moist southerly
flow. Temps and dewpts will remain below normal for late June with values
warming back to near normal by day 7.

&&

.AVIATION /15Z FRIDAY THROUGH TUESDAY/...
At KCLT and elsewhere: Lingering late morning MVFR cigs will
continue to scatter through Noon, with VFR conditions through the
day and breezy S/SW winds as the pressure gradient increases ahead
of the approaching front. Front pushes in this evening and tonight,
with convection developing across the mountains ahead of it. Some
question as to the amount of instability that will lead to TSRA, so
have included some PROB30s after about 06z for the Upstate TAFs and
KAVL, but only VCSH or PROB30 -SHRA for KHKY/KCLT. Will likely see a
wind shift by the end of the period for KAVL, with plentiful
moisture leading to another round of MVFR to possible IFR
restrictions.

Outlook: Abundant moisture will continue into Saturday with
associated restrictions and possible convection. The front will push
through on Sunday to usher in a period of drier weather through the
middle of next week.

Confidence Table...

            15-21Z        21-03Z        03-09Z        09-12Z
KCLT       High  90%     High 100%     High 100%     Med   60%
KGSP       High  98%     High 100%     High 100%     High  89%
KAVL       High 100%     High 100%     High 100%     High  84%
KHKY       High 100%     High 100%     High 100%     High  98%
KGMU       High 100%     High 100%     High 100%     High  94%
KAND       High 100%     High 100%     High 100%     Med   75%

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...HG/TDP
SHORT TERM...JPT
LONG TERM...JPT
AVIATION...HG/TDP



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