Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 170240

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
940 PM EST Mon Jan 16 2017

Above average temperatures will persist through mid week. A weak
cold front will approach the Carolinas from the west by late Tuesday
bringing increased chances for precipitation. A warm front will move
north over the Southeast on Thursday and Friday, bringing more rain
to the forecast area. A more significant low pressure system is
expected to develop over the region during the later part of the weekend.


As of 940 PM EST: Damming high remains in place across the area with
low clouds and patchy fog. Expect the clouds to continue through the
night with fog...likely dense...developing. Still too early to tell
where areas of dense fog will develop, but expect a dense fog
advisory will be needed at some point overnight into Tuesday. Radar
has been quiet, but still expect light showers off and on overnight,
with best chance from along the Blue Ridge west across the mountains.

Otherwise...surface high off the Delmarva with associated cool
pool/hybrid CAD has led to a cool and cloudy day across the area.
Weak upper ridging over the Appalachians remains in place with a
very dynamic system across the Plains lifting up and over the upper
ridge. Approaching front will elongate and occlude, but in the
meantime isentropic upglide over the cool dome (not really even
"cool" since temperatures are still above seasonal averages, but
closer than`s all relative though) has led to some
spotty showers especially in the upslope areas of the Southern
Appalachians. Hi-res guidance and CAMs have been a little more
aggressive with this showery activity so have not gone as high with
pops as those would suggest, but still decent chances especially
again across the upslope areas.

As we move forward in time, overnight into tomorrow, the damming
will slowly erode with the upper ridge flattening and the front
pushing into the Ohio and Mississippi Valleys. Upslope showery
activity will continue with plentiful cloudiness overnight, which
will again keep temperatures well above seasonal normals. Some
question as to how quickly the damming will erode tomorrow, and
since guidance is usually a little too fast, this could lead to some
bust potential with afternoon highs. For now have gone about 10
degrees above today`s highs for the Piedmont areas, but not such a
change across the mountains where some sunshine is peeking through
today. Pops will be on the increase from the northwest as the front
approaches  and moves into the mountains by the end of the period.


As of 230 PM EST Monday...An upper ridge will persist over the
Southeast states during the Short Term, with split flow to the west.
In the northern stream, a short wave will streak across the Great
Lakes Tuesday night, and exit off the East Coast by Wednesday
evening. This wave will be accompanied by a jetlet which will bring
a brief shot of upper divergence, mainly over the NC zones early
Wednesday. At the surface, an associated low pressure system will
pass by to our north, and drag a trailing cold front into western NC
from the north. The low-level flow will turn out of the NW ahead of
the front. The resultant downsloping will rob most of the area of
moisture and lift. The exception will be along the TN border, where
upslope flow should bring widespread showers. So PoPs range from
categorical west to slight-chance in the southeast. PoPs taper off by
around midday Wednesday. Temps will be a bit tricky, as cold air
advection ramps up in the NC zones, but not much to the south. I
blended in the MOS consensus to bump up highs slightly in the south.
Wednesday morning will start out warm in the 50s. Then temps warm
into the lower 70s across the GA/SC piedmont, but remain in the 50s
in the Northern Mountains.

Wednesday night and Thursday, the upper ridge amplifies behind the
short wave, but the axis shifts east of the area. This will bring
the deep-layer flow out of the southwest. There should be a lull in
PoPs, with weak surface high pressure crossing the area behind the
front. PoPs will increase in the west Thursday afternoon, as a low
pressure system begins to organize over the lower MS Valley. Temps
will remain well above normal. Lows mainly in the 40s, and highs
mainly in the 60s.


As of 230 PM EST Monday:  The medium range fcst period continues to
look wet as a series of upper/sfc waves sweep across the
southeastern states through the period.  The fcst kicks off on
Thursday evening as a closed upper cyclone rotates over the Southern
Plains, while shortwave ridging holds along the southeast shores.
The pattern will modify rather quickly into Friday as the upper low
slides north as it opens, while a surface wave moves through the OH
Valley.  As for sensible weather across northeast GA and the Western
Carolinas, moisture will spread into the region from the GOM
overnight into Friday morning, likely lifting isentropically atop a
weak surface ridge anchored along the Outer Banks, before
transitioning to showers as lapse rates increase via sfc warm
frontal passage.  With that, light/moderate rain is expected, the
heaviest of which looks to fall across Northeast GA and the western
most portions of SC as well as along the southern escarpment where
upsloping will be enhanced thanks to ample wswly H85 flow.
Fortunately given the progressive nature of the pattern, this system
looks to eject to the east by midday Friday leading to only a few
transient showers into the afternoon hours.

A brief lull in activity is favored by guidance on Friday night into
Saturday given a quick shot of upper ridging, while another upper
low develops across the Plains then moves sharply northward, as
resulting surface cyclogenesis spawns wave development along the
Gulf Coast.  This wave is progged to remain south along the I10
corridor, where scattered convection is favored on Saturday,
possibly spreading as far north as the I20 corridor.  At that point,
the focus shifts to the next upper low deepening across the Southern
Plains, and it`s eventual ely track into the lower OH and TN Valleys
on Sunday into Monday, all while a broad surface ridge shifts south
over New England attempting to drive a back door wedge front into
the region.  This stacked system and a potential wedge TMB could set
the stage for a convectively active Sunday evening/overnight.  In
addition, robust GOM moisture advection will lead to another round
of moderate/heavy rainfall potential, focusing yet again along the
southern facing slopes of the escarpment.  All in all, the mesoscale
details continue to be unclear with this late period system, however
guidance has been rather consistent regarding the overall synoptic
scale pattern.  Temperatures through the period look to start off
well above normal, cooling slightly throughout, albeit remaining at
or just above normal levels.


At KCLT and Elsewhere: Cold air damming remains across the region
keeping mostly MVFR cigs in place. Expect a return to IFR then LIFR
cigs overnight. VSBY will deteriorate as well with MVFR then IFR.
Cannot rule out LIFR or even VLIFR by daybreak, but locations and
timing are still in question. Expect any showers to be mainly over
the mountains and near the Blue Ridge. Should be a slow increase to
VFR VSBY and IFR cigs through the morning. CIGS may lift to low VFR
before the end of the period, but could see just MVFR by late
afternoon. Light ENE wind becomes SE then S overnight and continues
into the morning. S to SW wind develops for the afternoon, with low
end gusts possible.

Outlook: A moist airmass and sfc boundary will remain close to the
fcst area through Friday, with flight restrictions possible each day.

Confidence Table...

            02-08Z        08-14Z        14-20Z        20-00Z
KCLT       Low   43%     Low   54%     Med   64%     High  91%
KGSP       Med   77%     Med   65%     Low   53%     Med   73%
KAVL       High  87%     High  80%     Med   74%     Med   65%
KHKY       Low   49%     Med   66%     Med   61%     High  84%
KGMU       Med   76%     Med   65%     Low   51%     Med   75%
KAND       Low   41%     Med   66%     Low   42%     High  82%

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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