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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS62 KGSP 312332
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
732 PM EDT Sat Oct 31 2020

.SYNOPSIS...
Cool high pressure will weaken tonight as a cold front approaches
from the northwest. The cold front will cross the region Sunday,
ushering in the coldest air of the season for the early part of
next week. Dry high pressure will then linger across the area
through the middle part of the week.

&&

.NEAR TERM /THROUGH SUNDAY/...
-- Changed Discussion --
700 PM Update...Issued a High Wind Watch for the nrn NC mtns
effective Sun afternoon through daybreak Mon. A strong cold
front will mix down stg winds tomorrow evening and thru the
overnight. Winds will approach high wind criteria and due to the
recent rainfall and very moist soils...trees and powerlines
will likely be blow down. A high wind warning or wind advisory
will be issued on subsequent shifts.

The fcst is in good shape. Still seeing good Atl moist flux
interacting with sfc wedge making for widespread cloudiness with
Ci shield moving in from the west. May not get a good look at
blue moon, but there could be some breaks occasionally.

500 PM Update...Increased sky cover across the Upstate and NE GA as
se/ly moisture adv has increased atop the llvl wedge. This has held
localized temps down a few degrees and have adj/d the grids down in
these areas.

As of 230 PM: Sfc high pressure will migrate east off the New
England coast, while a strong cold front pushes into the Ohio
Valley tonight. The anticyclonic flow around the departing high will
advect some Atlantic moisture into the area this evening, deepening
overnight as decent isentropic lift develops atop the FA. Guidance
seems to be trending wetter with more robust QPF response. I`m
still reluctant to go likely or higher on PoP, given model track
record of overdoing QPF response in these shallow return-flow
situations. For now, have bumped up PoP to around 50% overnight,
highest across the Piedmont. At the very least, should see expanding
stratus deck across the entire area. Temps will be held up due to
strong WAA and the clouds, bottoming out in the upper 30s highest
peaks to mainly mid to upper 40s elsewhere. QPF should be light.

On Sunday, the strong cold front will cross the area during the day
as a deep upper trough digs across the region. The arrival of the
front will actually lower PoPs, except along the TN border, given
it will be dry and flow turns out of the WSW just ahead of it. The
biggest concern with the fropa will be the onset of gusty winds
in the mountains, with strong CAA ramping up by early aftn. Will
likely need a wind advisory for portions of the NC mountains
starting around midday tomorrow, but will let the midnight assess
one more cycle of guidance. Temps will be tricky, as skies clear
and some downslope flow develops east of the mountains. But the
CAA may be enough to overwhelm a lot of that. So sticking with
max temps a few degrees below model consensus. Still will be near
normal east of the mountains.
-- End Changed Discussion --

&&

.SHORT TERM /SUNDAY NIGHT THROUGH MONDAY NIGHT/...
As of 225 PM EDT Saturday: The first part the new week looks busy
with non-precipitating weather concerns, none of which will yet be
addressed beyond the HWO. After the axis of a relatively deep upper
trof crosses the region Sunday evening, we will be set up for a
classic advective freeze across the mtns, courtesy of cold advection
on a strong NW flow in the wake of the trof. However, the date on
Monday, that being 2 November, is problematic because by policy
the NWS does not issue Freeze Warnings across the mountains after
1 November.  That makes our expected advective freeze a day late
as far as the mountains are concerned. Meanwhile, the NC Foothills
and much of the NW Piedmont are also looking favorable for a freeze
early Monday morning, so we WOULD have to issue a Freeze Warning
there if the fcst does not change. It might ultimately be less
confusing to ignore the usual turn-off date for the mtns and issue
a Warning everywhere that freezing temps are expected (with the
exception of the nrn mountains which have been officially turned
off as of this past morning). Winds at 850 increase markedly late
Sunday evening with the guidance showing a 50kt wind at 850 with
cold advection, which is usually good for a Wind Advisory. We rarely
issue third-period advisories, so we will punt this to the next
shift to let them issue at a more appropriate time. Moisture looks
meager and limited in this NW flow on Sunday evening, such that any
precip is expected to remain to our north. Will not be surprised,
however, if some locations over the nrn mountains get their first
snow flurries of the season (almost on schedule it seems). We will
address that later as well. Needless to say, temps will be below
normal. On Monday, with high pressure building in throughout the
day and cold advection continuing, high temps will remain about
ten degrees below normal and will struggle to get out of the 50s
east of the mtns. There is some indication that orographic cirrus
will develop downwind of the higher terrain, which will help keep
temps cooler, maybe even a few degrees cooler than expected. The
sfc high will nose in from the southwest Monday night allowing
winds to diminish. Low temps early Tuesday will once again be down
in the frost range east of the mtns, but the air mass will be so
dry that frost may not be able to form in most areas across the
Piedmont and foothills of NC and the Upstate.

&&

.LONG TERM /TUESDAY THROUGH SATURDAY/...
As of 126 PM EDT Saturday: The medium range looks rather
quiet, even as the upper pattern changes slowly throughout the
week. Deamplification is expected through the middle part of the
week as the upper trof moves farther off the East Coast and a
flat upper ridge moves eastward. This should allow for surface
high pressure to set up shop over the srn/central Appalachians
on Tuesday, where a chunk of this sfc high will get stranded for
the rest of the week. The culprit in this development will be a
rex blocking pattern that forms to our west late in the week. The
result would be a building upper anticyclone that moves down over
the OH/TN Valley region to the Carolinas by the weekend. Confidence
isn`t all that great in such a blocking pattern, but for now,
the fcst will remain dry in spite of some weak return moisture
shown by the GFS next Saturday. In this pattern, temps may start
out a few degrees below normal during the middle of the week,
but end up about five degrees above normal by the end of the week.

&&

.AVIATION /00Z SUNDAY THROUGH THURSDAY/...
-- Changed Discussion --
At KCLT and elsewhere: A low level wedge will remain in place
overnight while good moisture flux will lift overhead and produce
-shra across the FA, beginning arnd 09z and not pushing east until
noon or the early afternoon. These showers will bring flight
restrictions, mainly low CIGs in the MVFR to IFR range during this
time. Winds will remain sw/ly across the non/mtns during the
afternoon and become gusty ahead of a cold front. At KAVL...winds
will remain se/ly then shift nw/ly arnd 20z with moderate gusts
developing.

Outlook: Clearing skies and gusty NW winds expected in wake of the
cold front Sunday aftn. Winds gradually weaken on Monday, followed
by quiet VFR conditions likely thru the end of next week.

Confidence Table...

            23-05Z        05-11Z        11-17Z        17-18Z
KCLT       High 100%     High  95%     High  83%     High  90%
KGSP       High  95%     High  86%     Med   65%     Med   65%
KAVL       High 100%     High  86%     Med   63%     High 100%
KHKY       High 100%     High  82%     Low   48%     High  80%
KGMU       High  95%     High  86%     Med   61%     Med   70%
KAND       High  95%     High  95%     Med   65%     Med   65%

The percentage reflects the number of guidance members agreeing
with the scheduled TAF issuance flight rule category. Complete hourly
experimental aviation forecast consistency tables are available at
the following link:

www.weather.gov/gsp/aviation
-- End Changed Discussion --

&&

.GSP WATCHES/WARNINGS/ADVISORIES...
-- Changed Discussion --
GA...None.
NC...High Wind Watch from Sunday afternoon through Monday morning
     for NCZ033-049-050-501-503-505.
SC...None.
-- End Changed Discussion --

&&

$$
SYNOPSIS...PM
NEAR TERM...ARK/SBK
SHORT TERM...PM
LONG TERM...PM
AVIATION...SBK