Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 152338

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
638 PM EST Sun Jan 15 2017

A cooler airmass will push into the region on Monday, but
temperatures rebound through mid-week as a cold front approaches
from the west with light rainfall.  Behind the front, temperatures
will cool slightly but remain above normal. A warm front will move
through the Southeast Thursday and Friday with another round of
showers likely while a more significant storm system moves into
the Southeast during the weekend.


As of 635 PM, Low level southerly flow over the surface boundary
across the NC Piedmont is leading to scattered showers this evening.
These showers should dissipate through the night as the flow becomes
more southwesterly and lift decreases. Still, there may be isolated
showers through the night with continued moist low levels and slowly
sagging frontal boundary.

Otherwise, a negatively tilted upper ridge will progress across the
MS River Valley to the Southern Appalachians today and tonight,
while an upper low moves from West TX to Northwest MO. At the
surface, a ridge will nose down the Easter Seaboard tonight and
Monday. A front aloft will lift north over this boundary, while
moisture from the Gulf of Mexico spreads east across the Gulf States
as a cold front reaches the lower MS River Valley.

The upshot of all this is that the best chance of precipitation
initially moves north of our area tonight and early Monday, then the
effects of Gulf Moisture reach the area later on Monday. Liquid
precipitation amounts are expected to be quite light. Instability
and shear will be insufficient for convection. Temperatures will
remain above normal under the upper ridge, but with a reduced
diurnal range due to cloud cover,


As of 220 PM Sunday: The upper flow pattern will become rather
complicated over the CONUS through the short range. A wave ejecting
across the Great Lakes Monday night should give way to a split-flow
pattern with a northern stream system digging across the Midwest
while a southern stream closed low churns over northwest Mexico
through Tuesday. East of these features, southwesterly low level
flow will increase across the southern Appalachians Monday night
through Tuesday with deeper moisture gradually pooling along an
approaching cold front. Will maintain a strong west to east gradient
in PoP for showers Tuesday afternoon - with warm max temperatures
throughout despite the clouds.

The northern stream system gets especially out of phase among the
model solutions Tuesday night through Wednesday, with the ECWMF
leading the faster camp, the ensemble means in the middle, and the
operational GFS slower and deeper through Wednesday. Sensible
differences, however, are not tremendous with the associated frontal
zone likely sliding southeast through the region sometime Tuesday
night through Wednesday, with some measure of NW flow downslope
drying east of the mountains later Wednesday afternoon. Any warm
sector thunder currently appears possible mainly in the very far SW
NC mountains before daybreak Wed. Will maintain very mild
temperatures with morning mins in the 50s and highs in the 60s all
but the higher terrain.


As of 230 PM EST Sunday:  The medium range fcst period kicks off on
Wednesday evening amidst the passage of a potent H5 shortwave, with
a favored position generally centered atop the Western Carolinas
at fcst initialization per the GFS/CMC, while the ECMWF is slightly
more progressive.  Elsewhere,  the persistent GOM upper anticyclone
is compressed/flattened thanks to said shortwave, as another closed
upper low strengthens over the Desert Southwest.  At the surface,
guidance does agree that a cold frontal passage will be underway,
with the front favored along/south of I85 by 00z Thursday, while
broad yet weak ridging moves in behind across the TN valley.

Pattern evolution through the remainder of the period is highlighted
by upper amplification of a ridge axis across the southeast, while
the old Desert Southwest upper cyclone migrates northeast into the
Central/Southern Plains Friday, before opening up across the Upper
Midwest on Saturday.  As a result, surface cyclogenesis over the
MidSouth is favored, with said low pressure system to move into
the OH Valley by Saturday.  The old weak/dry surface anticyclone,
which by this time will have setup along the east coast, will move
out to sea as the upper ridge axis does the same thanks to height
falls from the west.  With that, moisture looks to advect into the
region from the south by way of a H85 warm fropa, likely yielding
a period of isentropic upglide Friday night into Saturday.

Moving along, another brief period of shortwave H5 ridging to move
overhead early on Saturday will be quickly followed by additional
height falls Saturday night into Sunday while broad surface high
pressure anchored over the northeast wedges down the seaboard in
the lee of the Appalachians.  Additional H5 waves passing through
the southern stream across the Plains will lead to another round
of surface cyclogenesis in the MS River Valley, and thus additional
moisture advection and precipitation across the deep south to round
out the weekend.  At this point, although with some slight timing
differences, guidance seems to converge on a solution featuring a
final and much deeper H5 low diving through the Southern Plains
into the MS Valley late Sunday.  By that point the southeastern
CONUS looks to be rather moist and thus increasingly unstable
ahead of a deepening surface wave and cold front for Sunday night
into Monday.  The ECMWF is a bit faster with the evolution of this
late period system relative to the GFS, however both favor a pattern
for active weather, possibly yielding strong/severe convection and
heavy rainfall.  Said heavy rainfall threat looks to be maximized
along the southern escarpment where upsloping will be favored.
All said, at this range the details are a bit too muddy for any
mention in the outlook given lack of confidence on timing, as
well as the potential for coastal convection to block significant
convection northward into northeast GA and the Western Carolinas.


At KCLT and Elsewhere: Conditions will deteriorate from VFR early
this evening to MVFR then IFR overnight. NC sites will see
restrictions first with KAND the latest. LIFR expected around
daybreak. VSBY will improve by afternoon, but IFR CIGS will continue
through the afternoon. KAND will see MVFR for the afternoon. SHRA
over the piedmont early this evening will dissipate through the
night. Any restrictions with the SHRA will be brief. E to SE wind
will continue through the period at KCLT and KHKY. The SC sites will
see S to SW wind becoming E then ENE. KAVL will see N wind becoming

Outlook: A moist airmass and sfc boundary will remain close to the
fcst area through Thu and set the stage for flight restrictions each

Confidence Table...

            23-05Z        05-11Z        11-17Z        17-18Z
KCLT       Med   66%     Med   65%     Low   41%     Low   41%
KGSP       High 100%     Med   63%     Low   46%     High  94%
KAVL       High  94%     Med   75%     Med   68%     High  94%
KHKY       Med   66%     Low   58%     Med   75%     Med   66%
KGMU       High 100%     Low   48%     High  80%     Low   54%
KAND       High 100%     High 100%     Low   48%     High  87%

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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