Area Forecast Discussion
Issued by NWS Greer, SC

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000
FXUS62 KGSP 040757
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
257 AM EST Sun Dec 4 2016

.SYNOPSIS...
Increased moisture will cross our region from the west today and
linger into Tuesday. A strong cold front will arrive Wednesday night
bringing some of the coldest air of the season so far at the end of
the week.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 230 AM EST...A deep and vigorous upper low can be seen still
digging SEWD across northern Mexico this morning. This low is
tapping into tropical moisture from the Pacific and advecting it
into the southeast U.S. At the surface, a large area of high
pressure will shift east from the southern Great Lakes to roughly
along the Mid-Atlantic coast by early this evening. Moist isentropic
lift and WAA will strengthen a hybrid cold air damming wedge today,
keeping temps nearly steady in the upper 30s to mid 40s for most of
the area. A light to moderate steady rain is expect for most of the
day. Fortunately, limited instability and forcing should keep rates
under excessive levels today. QPF amounts thru 12Z Monday look to
range from about 0.7" north of I-40 to nearly 1.5" in the SW
mountains and adjacent GA/SC mountains with favored SLY upslope
flow. Forecast soundings still support high-elevation snow this
morning, especially in the northern NC mountains above about 5000
ft. However, temps should be above freezing everywhere but the
highest peaks. So little to no accumulation is expected. Warm air
advection should change all precip to rain by midday.

Tonight, a wave of weak low pressure will ripple east of the
area, veering the low-level flow to more westerly and allowing
precip to taper off overnight. There will still be a weak wedge
holding on, which will keep the area cloudy and perhaps somewhat
foggy. Temps will only drop a few degrees at most from the afternoon
highs.

&&

.SHORT TERM /MONDAY THROUGH TUESDAY/...
As of 245 AM EST Sunday: We begin the short term with a shortwave
trough pushing through the Great Lakes with its attendant front
across the eastern Carolinas, surface high pressure over the Ohio
Valley, and a slowly filling upper low beginning to push northeast
from Mexico into TX, meanwhile pulling Pacific and Gulf moisture
into the coastal states as surface cyclogenesis is induced along the
TX Gulf Coast. Behind the initial front, we`ll be in a bit of a lull
though with the subtropical jet right over us, will keep the trend
of low chance pops south with at best slight chance across the
northern tier. We might see some breaks in the clouds as well with
highs only a couple of degrees below seasonal normals on Monday.

Meanwhile the surface high will cross the Appalachians during the
day and begin to ridge down the Eastern Seaboard in a diabatically
enhanced classical CAD setup. The Gulf Coast low will lift northeast
in a Miller B scenario late Monday into early Tuesday, with
widespread moisture overtopping the cold dome. PW values between 1-
1.5" can be expected by Tuesday morning across the area, the upper
end of which is pretty darn close to record PW values. This is
fairly short-lived with the fast-moving system but could bring some
hefty rainfall amounts to portions of the Piedmont as the southern
of the two Miller B lows pushes northeast in the predawn hours. 6-hr
QPF values are 0.75-0.9" across the GA/Carolinas Piedmonts in our
area from 06z-12z Tuesday so this would be the period of greatest
concern for impacts from heavy rainfall. Storm total QPF ranges from
about 1.5" across the northern tier to almost 3" across the southern
tier. Additionally, with the damming in place and strong
ageostrophic adjustment, winds will pick up out of the NE Monday
night, with sustained winds 10-15kt and gusts up to 20kt. Certainly
nothing close to advisory criteria or anything like that but worth
noting.

Precipitation will exit quickly to the east during the day on
Tuesday, but with lingering moisture across the mountains with NW
surface flow and and SW flow aloft. Highs Tuesday will be highly
dependent on if the damming is able to erode earlier than
anticipated, but since usually guidance is too fast at eroding the
wedge, continued to lean slightly on the cool side.

&&

.LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/...
As of 145 AM EST Sunday:  The strong cold front will arrive from the
west by late Wednesday. Ahead of the front Max temps will be about a
category above normal which will make Wednesday the mildest day of
the whole week. There will be no inflow from the Gulf as low level
wind will be from a general west direction Wednesday into Thursday
morning shifting to NW by PM Thursday into Friday.  The moisture
starved environment associated with the cold front will yield very
little precip. Based on the latest run of the GFS, only precip will
be in the mountains being light snow behind the front with falling
thickness values. All that shrivels away by early Friday. A little
more precip on the ECMWF but that also ends abruptly early Friday
with much drier and colder air moving into the area.  Expect cold
air advection Friday and then light to no wind on Saturday as the
center of the cold surface high will be over the Carolinas and VA
early Saturday. Both the GFS and ECMWF have a wintry precip producer
arriving to our region later on Sunday lingering into next Monday.
That is after the current forecast so stay tuned for how this
evolves in the days ahead.

Temps a little above normal Wednesday then falling to 15 degrees or
more below normal for Friday and Saturday. Some moderation in Min
Temps Saturday night as cloudiness increases ahead of the next
system.

&&

.AVIATION /08Z SUNDAY THROUGH THURSDAY/...
At KCLT and Elsewhere: Conditions are starting out VFR, with mid
cloud bases in the 7000-10000 ft range. But conditions will
gradually deteriorate thru the wee morning hours and thru the day
today, as precip continues to moisten the low-levels. MVFR
conditions are expected to develop, as rain becomes steadier in the
9-12Z time frame, then into IFR mid- to late-morning. Rain will
begin to taper off this evening, but vsbys will remain low in
mist/fog. The guidance generally has LIFR CIGS developing from
midafternoon thru this evening. Winds will be generally NE to ENE
across the foothills and piedmont sites, and SE at KAVL.

Outlook: A brief lull is possible Monday, then another round of
heavier rain and widespread restrictions on Tuesday. Brief dry
weather is expected on Wednesday, with another front approaching
from the west.

Confidence Table...

            08-14Z        14-20Z        20-02Z        02-06Z
KCLT       High  83%     Med   65%     Med   74%     High  86%
KGSP       High  80%     High  83%     Med   66%     Med   77%
KAVL       High  85%     High  87%     High  83%     High  86%
KHKY       High  89%     High  81%     High  87%     High  86%
KGMU       High  80%     Med   79%     Med   68%     Med   77%
KAND       Med   73%     Med   75%     Med   73%     Med   72%

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...DEO
NEAR TERM...ARK
SHORT TERM...TDP
LONG TERM...DEO
AVIATION...ARK



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