Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 221436

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
1036 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.


1030 AM update: Seeing how unstable aftn profiles are on morning
RAOBs and HRRR/NAM Bufkit progs, raised PoPs a bit overall. Most
guidance still does not develop much if any QPF response in the
NW NC Piedmont, apparently keying on slightly more prohibitive
lapse rates above the PBL. I have cautiously kept PoPs there below
mentionable threshold but will monitor cu development over next
couple hrs.

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.

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 sfc-based inversions will will
dissipate this morning across the mtn valleys with VLIFR conds
improving thru 14z at KAVL. Low-end sfc winds aligned nw/ly with
little to no gust potential per vertical profiles. At KCLT winds
will veer e/ly thru the afternoon. A few -shra/tstms mainly across
the higher terrain so have included a VCTS group at KAVL and VCSH at
KHKY. Return to low CIGS/VSBY over the mtn valleys and adjacent
fthills overnight.

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...

            14-20Z        20-02Z        02-08Z        08-12Z
KCLT       High 100%     High 100%     High 100%     High 100%
KGSP       High 100%     High 100%     High 100%     High 100%
KAVL       High  91%     High 100%     High 100%     Med   62%
KHKY       High 100%     High 100%     High 100%     High  83%
KGMU       High 100%     High 100%     High 100%     High 100%
KAND       High 100%     High 100%     High 100%     High  83%

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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