Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 110350
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
1050 PM EST Sun Dec 10 2017

.SYNOPSIS...
Below normal temperatures and dry conditions will persist through
Monday. Mountain snow chances will return Tuesday as cold front
moves through the area. Dry high pressure will builds back in
Wednesday.

&&

.NEAR TERM /THROUGH MONDAY/...
As of 10:30pm EST Sunday:  Conditions are clear this evening with no
radar echoes and only a few high clouds streaming across the region
in northwesterly flow.  As dry upper trough swings by tonight, 850mb
winds shift from northwesterly to westerly and transitional zonal
flow will prevail on Monday before the next system due in on Tuesday.

Cold air is still in place with Monday morning lows expected to be 5
or so degrees below normal.  The exiting trough and clear skies on
Monday will allow Monday`s highs to warm-up to seasonal normals

Satellite loop showed a lot of snow melting today, but areas in the
mountains still have enough snow on the ground for some refreeze of
melt water to become black ice in places.  Snow melt ordinarily
increases chances for fog, but dewpoints are so low that models keep
RH values up all night, and there has been no sign of fog in
observations so far this evening.

&&

.SHORT TERM /MONDAY NIGHT THROUGH WEDNESDAY/...
As of 145 PM Sun: A sharp shortwave trough will swing across the
southern Appalachians Tuesday morning, accompanied by a cold front
and another prolonged period of CAA. The ensuing northwesterly winds
still support upslope showers along the Tenn border between late
Monday night and about daybreak Wednesday, with the best overlap
of winds and moisture looking to be sometime Tuesday evening. The
showers will mostly fall as snow, though a partial change to rain
is expected in lower elevations during the day. Model trends in QPF
remain slightly downward, and it still looks like snow totals will
be below advisory criteria. Temps will be quite cold, more than 10
degrees below normal, throughout the area Wednesday morning. The
combination of cold temps and brisk winds still could result in
sub-zero wind chills in elevations above 3500 ft. Wind gusts may
also reach wind advisory criteria in spots. These occurrences
could both be handled by a Wind Chill Advisory at some point,
if forecast trends hold.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/...
As of 2:45 PM EST Sunday: The upper level pattern still features a
northwesterly flow aloft across the eastern CONUS for the period in
the latter half of the upcoming new work week. Meanwhile, a parade
of energy spokes were riding the flow down into our forecast area
(FA) during this time frame.

At the surface Wednesday night and Thursday a series of weak surface
boundaries/wind shift areas will scoot across the region in the mean
flow. Moisture will be limited therefore we will maintain a dry
forecast at this time.

Meanwhile for Thursday night and Friday the GFS and Canadian models
were advertising a stronger shot of energy, helping to back the mean
flow, and rotating into our FA.  Moisture will have to come with the
upper level source, since the Gulf of Mexico is not involved. We
basically allowed POPS to ramp up Thursday night and Friday midday
(chance POPS at the moment) across the western North Carolina
mountains. We did not fan the precipitation to the east, in light of
the European response which was not as robust as the GFS and the
Canadian models. Absent the European models, other deterministic
guidance down the road might suggest raising POPS and upping
potential snowfall in the mountains. Elsewhere maintained a dry
forecast, although will have to watch for some steeper lapse rates
and perhaps some spotty showers of rain or snow in other sections of
our FA.

Once this feature moves through, Friday night and Saturday should be
dry. Next on the weather agenda is the system for Saturday night and
Sunday coming from the southwest. The models show a large spread, as
a result we kept POPS on the low side.

Temperatures will vacillate with each passing system during this
time frame, but generally near or just below normal.

&&

.AVIATION /04Z MONDAY THROUGH FRIDAY/...
At KCLT and Elsewhere:  Good VFR conditions are forecast for the
next 24 hours at all stations, with the region dry and in the
transition region between two synoptic systems, the first that
passed through on Friday, and the next one due in later in the week.
Light and variable northerly to southwesterly winds are expected.
Tonight, a few high clouds will pass over the region, now seen on
satellite, embedded in northwesterly flow aloft.

Outlook: Dry conditions expected at all sites through the early part
of the week. Another NW flow snow event could take place Tuesday and
Tuesday night, then again Thursday night and Friday, with some brief
restrictions possible at KAVL.

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:

www.weather.gov/gsp/aviation

&&

.GSP WATCHES/WARNINGS/ADVISORIES...
GA...None.
NC...None.
SC...None.

&&

$$
SYNOPSIS...SBK
NEAR TERM...WJM
SHORT TERM...Wimberley
LONG TERM...TS
AVIATION...WJM



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