Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 220755

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
355 AM 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.


The synoptic pattern will change very little thru the near term. A
strong closed low over the NW CONUS will act as a w/ly blocking
mechanism...while PTC Jose moves very little off the New Eng coast.
These features will keep a stg h5 ridge axis aligned across the
central states with sfc hipres ridged east of the Apps into the FA.

After the morning fg/stcu dissipates across the mtn valleys...high
levels of insol will allow max temps to reach a few degrees F above
normal. With sfc td/s remaining steady state in the low-mid
60s...expect deep layered instability to reach modest levels most
locales except across the ne/rn zones where relatively lower theta/e
air will mix in from the north due to enhanced flow on the back side
of Jose. Model moisture 4-panels show the higher avail llvl moist
relegated across sw/rn portion of the FA and with weak e/ly mech
lift and mtn top conveg...pulse sct shra/tstms will likely develop
this afternoon. A couple storms may become stg/svr producing
localized large hail or damaging winds...but with limited shear
these storms will be short-lived and isol.

Skies will clear for the most part outside of early debris clouds
and allow for good rad cooling...yet mins will be held abv normal
due to persistent high sfc td/s. With steep sfc-based inversions
expected...moist llvls will once again support fg/stcu across the
mtn valleys and fthills arnd daybreak.


As of 330 AM Friday: The pattern will remain rather stagnant through
the short term, and indeed through much of the long term, as the
East will remain under the grip of a high amplitude, mean upper
ridge through the period. The only notable change during the short
term will be the strengthening of the inverted surface ridge along
the Eastern Seaboard, as the upper anticyclone strengthens and
becomes centered over the Great Lakes/northeast Conus. The result of
this will be to drive drier and more stable air through the forecast
area on NE low level flow. Before the drier air overtakes the entire
CWA, sufficient instability is expected to remain across far western
zones (primarily the high terrain) to support isolated convection
Sat afternoon. After that, the remainder of the period is expected
to see a continuation of unseasonably warm conditions (with drier
air perhaps supporting min temps a little closer to climo), with
very little chance of convection/precip into early next week.


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: 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...

            08-14Z        14-20Z        20-02Z        02-06Z
KCLT       High  93%     High 100%     High 100%     High 100%
KGSP       High  93%     High 100%     High 100%     High 100%
KAVL       Med   77%     High 100%     High 100%     High  87%
KHKY       Med   75%     High 100%     High 100%     High 100%
KGMU       High  93%     High 100%     High 100%     High 100%
KAND       Med   75%     High 100%     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:




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