Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 230735

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
335 AM 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 315 AM EDT...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


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...A weak area of low pressure continues to spin off the
Grand Strand today, keeping a moist NE flow atop the area. A
stratocu deck can be seen across central NC, and is expected to
bring MVFR cigs to KCLT like last night. Guidance overall is more
pessimistic than what happened yesterday, so perhaps there`s a
better chance for IFR cigs for a while around daybreak. I will keep
the TEMPO for now. The MVFR cigs should lift to VFR by early
afternoon, then scatter out as dry air begins to filter in from the
N. A small chance for mainly sprinkles will be possible thru most of
the period, but too low to mention any SHRA in the TAF at this time.
Winds will persist out of the NE.

Elsewhere...As with KCLT above, moist NELY flow will bring
MVFR-level stratocu to most of the area by daybreak. The consensus
is for the clouds to get to the Blue Ridge near KAVL and south to
KGSP/KGMU, but not as far west as KAND. The clouds may lower to IFR
at KHKY, where a TEMPO will be kept. The low CIGS should lift back
to VFR by midday or early afternoon. At KAVL...guidance wants to
develop fog, but persistence suggests little, if any fog will
develop. I will keep a TEMPO for MVFR fog and stratus during the
hours around daybreak. Winds should change direction little thru the
period, staying out of the NE across the Piedmont and NNW at KAVL.

Outlook: The weak low pressure along the Carolina coast will finally
dissipate by Saturday, allowing dry high pressure to build 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...

            07-13Z        13-19Z        19-01Z        01-06Z
KCLT       High  90%     High  88%     High 100%     High 100%
KGSP       Med   76%     High  95%     High 100%     High 100%
KAVL       High  81%     High  93%     High 100%     High 100%
KHKY       Med   66%     High  87%     High 100%     High 100%
KGMU       Med   79%     High  93%     High 100%     High 100%
KAND       High  89%     High  92%     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:




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