Area Forecast Discussion
Issued by NWS Greer, SC

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000
FXUS62 KGSP 220520
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
120 AM EDT Fri Sep 22 2017

.SYNOPSIS...
A moist easterly flow will be developing on Friday followed by
drier and stronger high pressure this weekend. Tropical Systems Jose
and Maria will remain off the east coast.

&&

.NEAR TERM /THROUGH TODAY/...
As of 100 AM: Mainly clear conds across the fcst area with low stcu
and some fg developing across the srn mtn valleys. With previous
precip...calm conds...and steep sfc-based inversions expect most
valleys to support lowering vsby and perhaps some stcu arnd daybreak
disipating by 13z.

As of 1000 PM: PoPs were adjusted to remove mention of precip for
the rest of the night, as convection has dissipated over the area.
Temps still look on track per latest obs and guidance.

Otherwise, the sfc pattern remains somewhat stagnant, with high
pressure extending from eastern Canada down the Appalachian chain,
while Tropical Storm Jose remains over the western Atlantic. The
high is associated with a sharp upper ridge. A shortwave trough is
present over the Carolinas, with the axis of best DPVA straddling
the region now, advecting south. Mins will remain muggy and well
above normal. Mountain valley fog looks likely to result once again,
with patchy Piedmont fog, though the latter is not expected to be
any more widespread than it was this morning.

Friday will be another day dominated by the incumbent weak high
pressure, featuring above-normal sfc temps. Thicknesses will be
slightly reduced, however, suggesting maxes 2-3 degrees cooler
than Thursday. Still, given recent model performance and plentiful
sunshine, I went toward the warm end of guidance. Modest instability
is progged, and the easterly flow will help initiate storms over
the higher terrain; weak subsidence most likely will cap off any
activity over the NW NC Piedmont. A slight chance PoP still is
warranted over the Upstate and NE GA. Marginally dry profiles
imply an isolated severe storm could develop.

&&

.SHORT TERM /TONIGHT THROUGH 6 PM SATURDAY/...
As of 205 PM EDT Thursday: A weak upper low over the Carolinas will
sink south to the FL panhandle on Saturday as ridging strengthens
over the Great Lakes and mid-Atlantic. The center of the ridge moves
east on Sunday and a ridge axis builds south toward the Carolinas.
At the surface, weak high pressure slowly builds to the north then
noses southeast into the area through the period. This sets up weak
northeasterly flow across the area. Drier low level air moves in
from the NE on this flow and subsidence develops as Maria moves
northward well off shore of GA and SC. Instability diminishes
through the period with the drying and subsidence. Expect some
lingering isolated convection across the mountains Saturday where
moisture is best and LFC levels will be low enough for convection to
develop. Dry conditions expected elsewhere on Saturday and all areas
Sunday. Highs and lows will be around 5 degrees above normal
Saturday then maybe drop a degree or two on Sunday.

&&

.LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/...
As of 100 PM EDT Thursday: Dry and warm conditions will continue
into the start of the new workweek with ridging lingering atop the
southern Appalachians.  Temperatures will change little Monday and
Tuesday featuring readings 5 to 7 deg f above climo.  By Wednesday,
even though the ridge center atop the NE conus gets pinched off, the
SE conus remains in a subsidence regime between the Northern Plains/
Rocky Mtn l/vw trough and TC Maria.  At this point, there seems to
be enough s/wv ridging lingering acrs the SE Conus into the new day
7 for the fcst to remain dry.  The streak of above normal
temperatures are expected to linger as well through the end of the
period.

&&

.AVIATION /05Z FRIDAY THROUGH TUESDAY/...
At KCLT and Elsewhere: Fairly steady state conds will persist over
the TAF period. Most locales will remain VFR with strong hipres
remaining over the area. Steep llvl lapse rates will develop this
morning in the mtn valleys and will expect some IFR or perhaps lower
VSBY at KAVL arnd daybreak. With the recent precip across the wrn
half of the FA...will go with IFR/MVFR VSBY at KAND and KHKY as
well. Low-end sfc winds aligned nw/ly with little to no gust
potential per vertical profiles. Some afternoon -shra/tstms mainly
across the higher terrain so have included a PROB30 group at KAVL.

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

Confidence Table...

            05-11Z        11-17Z        17-23Z        23-00Z
KCLT       High 100%     High  83%     High 100%     High 100%
KGSP       High 100%     High  83%     High 100%     High 100%
KAVL       High 100%     High  90%     High 100%     High 100%
KHKY       High 100%     High 100%     High 100%     High 100%
KGMU       High 100%     High  83%     High 100%     High 100%
KAND       High 100%     High  83%     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...CSH
NEAR TERM...ARK/SBK/Wimberley
SHORT TERM...RWH
LONG TERM...CSH
AVIATION...SBK



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