Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 231743

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
143 PM EDT Fri Sep 23 2016

A broad upper ridge and surface high pressure will build over the
region today and Saturday as temperatures rise well above normal
again. A slightly cooler, wetter trend will beging Sunday as a
frontal boundary settles into the area from the north. Unsettled
weather is likely to linger through the first half of next week.


As of 130 PM EDT Friday:  Llv stratus continues to highlight the
skies across the eastern third of the fcst area this afternoon,
with further eastward advection and scattering expected through
the immediate near term.  Thus, blended in latest consshort for
sky while also making a few tweaks to pops by way of keeping the
lower piedmont at slight chance levels for a few more hours given
light/weak radar returns as well as a few sfc obs.  Otherwise,
tweaked hourly t/td trends and left the remainder of the fcst as
it was for this update.

Previous Discussion:  A weak area of low pressure that has persisted
along the Carolina coast, will continue its weakening trend
today, as a high-amplitude ridge tries to nudge eastward across
the Mississippi Valley. This should result in a little backing of
the low-level flow from NE to N/NE, which will begin to bring some
drier air back into the area. Thicknesses also rebound, and allow
max temps to rise back above normal this afternoon. As for PoPs,
there will continue to be an isolated shower threat in the SE corner
of the CWFA. There also may be enough instability for an isolated
shower or two along the southern Blue Ridge escarpment toward NE GA.

Tonight, weakening low-level flow remains out of the NE, but
guidance in good agreement on continued dry air wrapping around
high pressure to our NW. So expect a dry night with perhaps less
cloud cover than last few nights. Temps will be about 6-8 degrees
above normal.


As of 300 AM Fri: Mostly sunny conditions return Saturday as an
upper ridge moves over the Southeast, and sfc high pressure begins
to build down the Eastern Seaboard, subsidence keeping convection
at bay. Temperatures should top out around 90 across most of the
Piedmont, with upper 80s in the mountain valleys. As the surface
high continues to push south, a backdoor cold front effectively
reaches western NC by late Sunday. Max temps will still be above
normal, but perhaps 5-7 degrees cooler than Saturday. Lower heights
aloft will enhance lapse rates to the point that isolated to widely
scattered showers and storms are possible across the area. Upglide
over the front becomes better defined Sunday night into early
Monday, warranting a slow increase in PoPs overnight.


As of 130 AM Fri: The previous two medium-range shifts have been
unable to make an constructive change to the fcst, which is
understandable given the remarkable inconsistency seen between recent
model cycles and between the GFS and EC. Fortunately for all of us in
the weather community, the latest round of guidance is in "moderate
agreement" as to how the pattern evolves early next week.

High pressure will be centered over eastern Canada and the NE CONUS
Monday morning as a low pressure system moves into the western Great
Lakes region. The models do diverge for a time in the subsequent
36-48 hours, mainly differing in how the low advances east toward
that sharp sfc/upper ridge, and how far south the backdoor cold front
pushes ahead of it. At least somewhat unsettled weather could be
expected around here through midweek, with upglide-driven activity
possibly giving way to warm-sector activity, before eventually
culminating in a cold fropa. Temps likely will be near if not a
little below normal early in the week. Interestingly, following that
fropa late Wed or Thu, the GFS, EC, and some of the GEM ensemble
members come back into agreement on sprawling high pressure pushing
back into the Southeast, and the trough starting to cut off again
over the Northeast. This pattern suggests we`re likely to see dry and
slightly cooler conditions for the end of the work week.


At KCLT:  VFR through the taf cycle.  Persistent low pressure along
the Carolina coast has begun to open up and shift slightly east.
As a result, am expecting current bkn mvfr to sct to at least
low vfr through the afternoon, before lifting to solid vfr into
the overnight.  As such, winds will remain light/moderate out of
the n/ne before calming overnight as well.  Guidance does hint at
the possibility of mvfr visbs spread about the region on Saturday
morning, however opted to keep any mention from taf at this point.
Beyond that look for skc and light ne winds though midday.

Elsewhere:  Remnant stratus across region will continue to
sct/erode from the west to the east through the afternoon.
As such am expecting vfr conditions at all sites through the
evening/overnight before patchy fog develops around daybreak.
The best chances for said fog being at lifr/ifr levels will be
at KAVL, while mvfr levels are possible at the remaining sites.
That said, confidence in said restrictions at KGSP/KGMU is rather
low at this point, however given fcst lows and current xover temps,
opted to include in taf.  Otherwise, trends similar to that of
KCLT above for Saturday.

Outlook: The weak low pressure along the Carolina coast will finally
dissipate by Saturday, allowing dry high pressure to filter in
from the north. A back door cold front will push into the region
late Sunday, bringing increased moisture for early next week.

Confidence Table...

            17-23Z        23-05Z        05-11Z        11-12Z
KCLT       Low   56%     High 100%     High 100%     High  83%
KGSP       High  94%     High 100%     High 100%     Med   66%
KAVL       High 100%     High 100%     High 100%     Med   66%
KHKY       High 100%     High 100%     High 100%     Med   66%
KGMU       High 100%     High 100%     High 100%     High 100%
KAND       High 100%     High 100%     High 100%     Med   66%

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:




SHORT TERM...Wimberley
LONG TERM...Wimberley
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