Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 220052

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
852 PM EDT Thu Sep 21 2017

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.


As of 745 PM: Convection already waning as we lose daytime heating.
The current PoP trends look on track, and only minor tweaks were
made to the sky/temp/dewpt for the evening/overnight hours with this

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. Cloud cover and PoPs will diminish
with the end of diurnal heating this evening. The high pressure will
bring increasingly easterly flow tonight but there is not enough low
level moisture progged to suggest nocturnal stratus will result.
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.


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.


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


At KCLT and Elsewhere: Not much change in the weather pattern over
next 24-36 hours. Isolated SHRA and TSRA already dissipating at
start of 00z TAF period, leaving just a few CU and CI for the
evening hours. Much like last couple nights, expect mountain valley
fog (but basically a coin flip whether it impacts KAVL), while the
Piedmont should stay VFR. The exception is with increasing dewpts,
guidance is trending toward some patchy MVFR vsby around KAND and
KHKY. Mainly mountain-triggered convection expected again Friday,
with PROB30 for KAVL during the mid-to-late aftn. Coverage elsewhere
will be very isolated. Winds will be light out of the N to NE or VRB
to calm overnight, then NE generally 5 kts or less Friday.

Outlook: Chances for diurnally favored showers and thunderstorms
remain in the fcst again Friday, but precip chances are a bit lower
over the weekend and early next week. Fog and/or low stratus are
likely to return in the mtn valleys each of the next few mornings.

Confidence Table...

            01-07Z        07-13Z        13-19Z        19-00Z
KCLT       High 100%     High 100%     High 100%     High 100%
KGSP       High 100%     High  96%     High  96%     High 100%
KAVL       High  96%     High  83%     High  96%     High 100%
KHKY       High 100%     High  96%     High  96%     High 100%
KGMU       High 100%     High 100%     High 100%     High 100%
KAND       High 100%     High  96%     High  96%     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:




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