Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 170602

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
102 AM EST Tue Jan 17 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 1255 AM, widespread low clouds persist across the area early
this morning within lingering cold air damming regime. The main
concern overnight will surround the potential for dense fog, as the
surface cool wedge is compressed from the south and east, and from
above. In fact, we are already seeing some patchy dense fog across
the far southern zones, and would not at all be surprised to see
this gradually expand to the northwest. Nevertheless, will stick
with the usual strategy of waiting to see evidence that the dense
fog is expanding before considering a DFA. Otherwise, spotty showers
continue across portions of western NC, and will maintain low pops
there through the early morning.

As we move forward 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,
and cigs have lowered to IFR or LIFR at the main TAF sites. LIFR
should expand to include all terminals by 09Z or so. Visby has also
reduced to IFR or less at KHKY and KAND, and these conditions should
also expand to include the other main TAF sites as well. The main
area of uncertainty is just how low cigs and visby will become, as
VLIFR conditions cannot be ruled out anywhere, but will be most
likely at KAND, where 1/4SM is tempo`d btw 08-12Z. Elsewhere, have
generally limited tempos to 1SM, but this will need to be closely
monitored through the morning. The other area of uncertainty is how
quickly conditions will improve later today. Will generally allow
IFR/LIFR conditions to persist through the morning, with conditions
improving to VFR at most terminals by around late afternoon. Winds
will generally be light and variable through sunrise or so, but are
expected to become SW at around 10kts by early afternoon.

Outlook: A moist airmass and sfc boundary will remain close to the
fcst area through Friday, with flight restrictions possible each
day. Surface low pressure approaching from the southwest will bring
chances for widespread precip to the area Thu and Fri.

Confidence Table...

            06-12Z        12-18Z        18-24Z        00-06Z
KCLT       Med   72%     Med   64%     High  94%     High 100%
KGSP       Med   72%     Med   68%     High  89%     High  98%
KAVL       Med   72%     Med   68%     Med   65%     High  84%
KHKY       High  87%     Med   76%     High  86%     High  86%
KGMU       Med   75%     Med   74%     High  88%     High  97%
KAND       Med   72%     Med   69%     Med   79%     Med   68%

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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