Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 040009

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
709 PM EST Sat Dec 3 2016

Increased moisture will return from the west on Sunday and linger
into Tuesday. A strong cold front will arrive early Thursday
bringing some of the coldest air of the season so far at the
end of the week.


As of 645 PM EST: Moisture return to the southern tier of the
forecast area has been a bit faster than progged and the onset of
PoPs will be hastened and then increased through the overnight
hours. The near-term convection allowing models, including the
latest and time-lagged versions of the HRRR, appear to have a good
handle on this faster timing and will be followed. The 18Z models
and latest RAP have warmed northern mountain and mountain valley
profiles a bit for the overnight hours, but I`m hesitant to back off
on the mixed precip (mainly snow) mention overnight since the wet
bulb profiles remain quite cool. Will generally follow the earlier
trends of increasing snow PoPs primarily along the northern Blue
Ridge overnight, but any high elevation accums will be very light
based on all the ensemble data.

Otherwise...a closed H5 cyclone centered over NW Mexico continues to
deepen as moisture lifts N/NE across the MS Delta region into the
TN/OH valleys and extreme southern Appalachians. Surface high
pressure remains centered over the southern/central Appalachians
late today and continues to reinforce a dry llv airmass.  The
atmospher will moisten with time from the top down with likely to
categorical PoP features west of I77 by 12z - spreading across the
entire fcst area by midday Sunday. Temperatures will slowly warm
into late morning across the entire fcst area leading to all rain by
midday as highs top out in the upper 30s across the mtns to upper
40s over the Piedmont. Rainfall amounts through Sunday afternoon are
fcst to be around 1-1.25 inches across the southwest/central NC mtns
and northeast GA, tapering down to the east with a half to quarter
inch favored at GSP and CLT respectively.


As of 215 PM EST Saturday: A split flow pattern early in the period
evolves into a single flow Atlantic ridge and broad central and
western CONUS trough by the end of the period. The northern wave of
the split flow on pushes a frontal boundary across the area. The
combination of deep moisture and synoptic scale lift, along with
isentropic lift, will spread rain across the area through the night.
Although surface temps across the Northern Mountains will be in the
mid 30s overnight, a nearly 10 degree C low level warm nose will
keep precip as all liquid. Lows will be around 5 degrees below
normal. QPF values will range from tenth to a half an inch from
north to south.

The moisture and lift move east and south of the area early Monday
as high pressure builds in from the north and sets up in a cold air
damming pattern. As this takes place, the southern stream upper low
over the Rio Grande opens up and moves across Texas. Short wave
energy moves through the flow ahead of the low and across our area.
The associated surface low moves east along the Gulf Coast spreading
a moist southerly flow across the SE CONUS. Precip spreads back into
the area from the SW in response. QPF will be light. Temps will be
tricky with the damming high setting up, but precip tapering off
across portions of the area. Expect highs generally in the low to
mid 50s, but they could be higher where precip ends and lower where
it lingers.

Precip develops in earnest Monday night as the upper low tracks into
MS and the surface low takes on a Miller B pattern. Deep moisture
returns, along with strong synoptic and isentropic forcing. This
will strengthen the damming high across the area. As the surface
lows track east on Tuesday, the southern wedge boundary does lift
north toward the area. However, expect it, and any resulting
instability or thunderstorms, to remain to our south as well. Still,
given the PW values and strength of the forcing, expect QPF values
to range from around 0.75 inches near the TN border to 1.5 inches
along the southern tier of the CWFA. Lows Monday night will be
around 10 degrees above normal with all liquid precip. Highs will be
near normal across the mountains where the damming influence is
less, to around 5 degrees below normal elsewhere.


As of 245 PM EST Saturday: A surface boundary should be south of our
county warning area (CWA) Tuesday evening as a deamplifying upper
level trough and vort max quickly sweep northeast into Virginia.
This will allow any lingering POPS to end quickly in the evening.

Wednesday a rather non descript pattern as the atmosphere reloads to
the west, and the surface pattern across our region remains "baggy"
with a weak flow. Conditions should remain dry for the balance of
the day.

A strong H5 trough will rotate into the middle Ohio Valley Wednesday
night and Thursday, signaling a change in our weather pattern. This
will allow a shot of cold air to begin a plunge into the region.
Thermal structure continues to show a downward trend in thickness
and H85 temperatures from late Wednesday night through Thursday -
at least.

We will continue with low POPs from late Wednesday night into the
wee hours Thursday night - with weak vorticity advection/cold air
advection and a bit of moisture. Deepest moisture should be in our
North Carolina mountains. Speaking of our North Carolina mountains
it appears to be cold enough for a change to all snow showers,
although precipitation amounts should be light at the moment.

Cold high pressure will then build into the region Friday and

Temperatures around normal Wednesday will start a much colder trend
in the Thursday through Saturday time range, perhaps some 10 to 15
degrees below normal.


At KCLT and Elsewhere: Profiles continue to steadily moisten from
the top down this evening but precipitation has been breaking out
from the southwest a bit quicker than progged. Still anticipate VFR
conditions through at least 06Z west to 08Z east with gradually
improving light rain coverage. Conditions will deteriorate to
steadier MVFR conditions from KAVL to the Upstate TAF sites, but
take a few hours longer at KHKY and not reach KCLT until 15Z. Any
onset precip at KAVL is expected to be liquid, but profiles remain
interestingly cool in the higher terrain nearby. Lowering MVFR
conditions through the day on Sunday will tend toward IFR during the
afternoon along with steadier moderate rain. Expect winds to adjust
back more solidly to ENE to NE east of the mountains as the rain
spread in, but with SE flow at KAVL.

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

Confidence Table...

            00-06Z        06-12Z        12-18Z        18-00Z
KCLT       High 100%     High 100%     High  89%     High  86%
KGSP       High 100%     High  89%     Med   75%     Med   76%
KAVL       High 100%     High  83%     High  84%     High  96%
KHKY       High 100%     High  93%     High  90%     High  91%
KGMU       High 100%     High  90%     Med   76%     Med   77%
KAND       High 100%     High  87%     High  86%     High  84%

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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