Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 221802

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
202 PM EDT Fri Sep 22 2017

Drier and stronger high pressure will develop over the weekend and
remain through at least the middle of next week. Tropical Cyclones
Jose and Maria will remain off the east coast.


As of 145 PM: A somewhat blocked pattern persists over most of
the eastern CONUS; an anticyclone extends from Texas to the Great
Lakes, but is undercut by a weak upper low over the Southeast. At
the sfc, high pressure centered to our north continues to drive
a light northeasterly flow into the CWFA. Warm and humid sfc
conditions combined with modest lapse rates aloft will result
in aftn instability. The easterly flow should kick off scattered
showers/storms over the mountain ridges, with more isolated cells
developing over mainly the SC/GA zones, where dewpoints are a bit
higher and subsidence slightly weaker. Dry profiles and weak shear
are similar to those seen the past couple of days, when a couple of
storms managed to produce damaging winds and severe hail. Slightly
lesser coverage is fcst today, though the isolated severe threat
still exists.


As of 150 PM Friday: Upper ridging builds south into the area
from the Great Lakes and mid-Atlantic on Sunday and remains
through Monday although it does weaken. Surface high pressure
follows a similar pattern while Maria moves north well off the
GA and SC coast. The result will be a dry northeasterly flow
keeping stable air over the area. Despite the NE flow, thickness
levels remain high keeping highs around 5 degrees above normal
each day. Fair skies and the drier air mass will allow temps to
fall overnight, but lows also remain around 5 degrees above
normal each morning.


As of 340 AM Friday: Very little change in the sensible weather is
expected through much of next week, as upper ridge remains
entrenched across the eastern Conus, while Tropical Cyclone Maria
should remain off the Carolina coast, not impacting our forecast
area at all. Dry and very warm conditions will therefore persist
through at least Wednesday. There are some hints in the global model
guidance of a potential pattern change toward the end of next week,
as some of the more reliable deterministic guidance sources depict
the beginnings of a break down in the eastern ridge by Day 7. Even
if the models are on to something, any change in sensible weather
impacts for our area would most likely be beyond the end of the
current forecast cycle.


At KCLT and Elsewhere: High pressure and summerlike conditions will
be the norm again this period. Easterly/upslope low-level flow will
drive mountain convection this aftn, which has prompted VCTS mention
at KAVL. Humid sfc conditions also will lead to instability over
the Upstate sites, though SHRA/TSRA are expected to be too isolated
to warrant TAF mention. Low VFR cu and precip chances dissipate
at sunset. Winds will be light and VRB tonight by and large, but
should prefer N to NE. Crossover temps are expected to be reached in
portions of the area tonight, which will lead to fog formation and
MVFR vsbys for KHKY/KAND, and IFR in the mtn valleys and at KAVL.

Outlook: Precip chances will wane over the weekend and early
next week. With clear skies and calm conditions, fog and/or low
stratus are likely to return in the mtn valleys each of the next
few mornings.

Confidence Table...

            18-24Z        00-06Z        06-12Z        12-18Z
KCLT       High 100%     High 100%     High 100%     High 100%
KGSP       High 100%     High 100%     High  91%     High 100%
KAVL       High 100%     High 100%     Low   46%     High  81%
KHKY       High 100%     High  97%     High  89%     High  94%
KGMU       High 100%     High 100%     High 100%     High 100%
KAND       High 100%     High 100%     High  94%     High  94%

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:




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