Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 040224

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
924 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 920 PM EST: Moisture return on weak upglide flow continues to
invade the forecast area in fits and spurts this evening. We appear
to be lacking a broad region of persistent upglide and the moisture
is developing from the top down in profiles that were quite dry at
onset. While many Upstate and NE GA locations have reported light
rain from time to time, amounts have been quite light as
considerable evaporation continues beneath the high cloud bases.
Still, anticipate the moisture steadily working its way to the
surface through the overnight hours and gradually spreading
northward. The main problem at this point is that mountain
temperatures are starting off quite chilly along the higher ridges.
There are plenty of lower to middle 30s late evening ridge top
temperatures and dewpoints in the 20s will support more cooling
despite the clouds. Have thus expanded the snow mention a bit across
the Smokies/Balsams and throughout the northern mountain valleys.
Will also have ridge top accumulations now reaching about an inch or
slightly more from Mt. Mitchell to Beech Mountain, but with just a
trace to a few tenths along mid slopes and into the higher mountain
valleys. The lower valleys should remain liquid. There is still some
concern that a very modest warm nose could develop even where the
temp hits 32 and perhaps mix in some sleet at times along the ridges.

Otherwise, a closed H5 cyclone centered over NW Mexico will deepen
as moisture lifts NE across the MS Delta region and toward the
extreme southern Appalachians. Surface high pressure remains
centered over the southern/central Appalachians this evening to
reinforce the dry low level airmass. The atmosphere will moisten
with time from the top down with likely to categorical PoP featured
west of I-77 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 late this evening, with precipitation managing to reach
the ground quickly at the Upstate TAFs despite the relatively high
clouds bases. Still anticipate VFR conditions through much of the
nighttime hours but with more solid MVFR cigs developing with
steadier light rain 09Z at KAND to 15Z at KCLT, and IFR possible by
late in the period with some moderate rain. Precip at onset at KAVL
is expected to be liquid, but profiles remain interestingly cool in
the higher terrain nearby. Otherwise, rain is expected throughout on
Sunday. Expect winds to adjust back more solidly to ENE to NE east
of the mountains as the rain spreads 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...

            02-08Z        08-14Z        14-20Z        20-00Z
KCLT       High 100%     High 100%     High  91%     High  84%
KGSP       High 100%     Med   79%     Med   77%     Med   79%
KAVL       High 100%     High  83%     High  83%     High  96%
KHKY       High 100%     High  90%     High  93%     High  86%
KGMU       High 100%     High  83%     Med   77%     Med   79%
KAND       High 100%     High  83%     High  84%     High  94%

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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