Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 090831

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
331 AM EST Sat Dec 9 2017

The wintry storm system will depart today, but moist northwest winds
will bring another shot of snow to the North Carolina mountains
tonight. Cool temperatures and dry weather will return Sunday and
persist through early next week.


As of 320 AM EST Saturday: Been watching a wide swath of light
precip extending from western NC down across metro ATL to the FL/AL
Gulf Coast early this morning...and waiting for it to start making
some eastward progress as suggested by the model guidance. So far
that hasn`t happened, but think that will gradually change as we
work toward daybreak. Thus, after some minor delay, the fcst still
features precip prob ramping back up to likely/categorical from west
to east through 12Z. Temp profiles are such that most of the precip
will fall as snow, with a transition to rain/sleet across the SE
fringe. The model guidance depicts a swath of upper divergence and
mid-level frontogenesis sustaining the light precip moving up from
metro ATL and across the Foothills/Wrn Piedmont of the Carolinas
this morning, with the potential to drop another inch or two across
the region along and N/W of the Interstate-85 corridor. Altho
additional accumulation will not reach the equivalent of warning
criteria, since this is an ongoing event, think it wise to leave
the Warning/Advisory orientation unchanged, at least until we see
how the new band of snow behaves. The main short wave will sweep
eastward during the period from late morning to mid-afternoon,
which should bring an end to the precip from west to east. Cloud
cover may hold on a bit longer than thought earlier, so high
temps today have been bumped down a bit after also factoring in
the new snow cover. Think the end time of the Warning/Advisory
also looks reasonable, thus we will try to let it ride. Across the
mtns, this will afford us a brief break of a few hours, however,
a trailing vort max will dive down across the region and could
bring renewed snow shower activity to the Smokies beginning in
mid- to late-afternoon, so precip chances ramp back up starting
there. The passage of this trailing wave will pull the flow around
to more northwesterly for the late afternoon and tonight. The NW
flow will have sufficient left-over moisture to work with, thus snow
showers appear likely on the TN border this evening and overnight,
perhaps accumulating another inch or two. Some of the snow could
make it as far east as the Asheville area. This could require
another Winter Weather Advisory at least for the TN border zones,
but we will allow the ongoing event to end first before another
Advisory is issued for the mtns. Temps tonight will be seasonally
cold...teens in the mtns and low/mid 20s over the Piedmont.


As of 300 AM Saturday: An upper trough axis will briefly pivot east of
the area and flatten somewhat Sunday into Monday, as sfc high
pressure settles over the Deep South. A trough of low thicknesses
will be over the area on Sunday. Despite mostly sunny skies and a
downslope NW flow, temps will struggle to rebound from Saturday`s
cold readings. A more noticeable rebound expected on Monday, as
thicknesses increase and flow maintains some downslope. Highs about
10 deg below normal Sunday and near normal on Monday.

Monday night thru Tuesday, another vigorous shortwave will dive into
the longwave and dig the trough over the area. A quick shot of
strong DPVA will cross the southern Appalachians on Tuesday,
bringing a brief NW flow event to the NC/TN border during the day.
The 00z models seem to have trended a little lower in PoP/QPF. But
still expect at least a few hours of scattered snow showers. At this
point, it looks sub-advisory, due to the short duration. Temps will
be a little cooler than Monday, as NWLY CAA ramps up.


As of 230 AM EST Saturday: A deep upper trough will be in place over
the eastern CONUS, with the trough axis positioned over the
Carolinas to start the medium range 00Z Wednesday. A period of NWFS
will be tapering off at the start of the period, with limited
additional accumulation expected Tuesday night as the trough axis
and best moisture and upper support shift off the east coast.
Wednesday will be quite chilly, with maxes and mins 10-15 degrees
below average as deep upper troughing persists over the eastern

Upper troughing will persist through Thursday as a series of
shortwaves round the H5 trough base before a clipper-type system
cuts across the area. It will drag a trailing front behind it,
though moisture will be so anemic outside of the mountains that no
QPF response is anticipated in the SC/NC Piedmont and Foothills. In
the higher terrain, another period of NWFS is expected to commence
as the clipper skirts by to the north on Friday. Temperatures will
moderate back towards average by the end of the work week.


At KCLT and elsewhere: Currently in the middle of a hole in the
lower overcast, with MVFR and some VFR ceilings mainly over the
Piedmont. Over the next few hours, the IFR ceiling is expected
to return as the next round of precip moves up from the SW. Have
that timed around 09Z and the most likely precip type will be light
snow, possibly mixed with light rain. Wind should stay N to NE. The
model guidance, especially the HRRR, shows a band of light precip
moving across the region in the early- to mid-morning hours. As
this happens, terminals should all go back to IFR/LIFR. As the
band moves off to the east, we should start to see an improvement
to MVFR in the late afternoon with a wind shift to SW, then VFR
in the early evening with a wind shift to NW.

Outlook: Dry conditions expected at all sites on Sunday and into
early next week.  The possible exceptions would be KAVL with
potential for northwest flow snow Saturday night.

Confidence Table...

            15-21Z        21-03Z        03-09Z        09-12Z
KCLT       High  81%     High  82%     Med   68%     Low   56%
KGSP       Med   70%     Med   75%     High  83%     Med   64%
KAVL       High  94%     High  85%     Med   70%     High  87%
KHKY       High 100%     High  83%     Med   66%     High 100%
KGMU       Med   76%     High  86%     High  85%     Med   63%
KAND       Med   76%     Med   65%     High  90%     Med   61%

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:


GA...Winter Storm Warning until noon EST today for GAZ010-017-018.
     Winter Weather Advisory until noon EST today for GAZ026-028.
NC...Winter Storm Warning until noon EST today for NCZ033-035>037-
     Winter Weather Advisory until noon EST today for NCZ071-072-
SC...Winter Storm Warning until noon EST today for SCZ001>003-
     Winter Weather Advisory until noon EST today for SCZ004-009-


LONG TERM...Carroll
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