Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 191139

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
639 AM EST Thu Jan 19 2017

A warm front moving north over the region through Friday in
combination with low pressure headed north toward the Great Lakes
will bring more rain to our area, mainly tonight. A more significant
low pressure system is expected to track across the region this
weekend, bringing rain and thunderstorms for Saturday, Sunday, and
Monday. High pressure will build into the region for the middle of
next week.


As of 635 AM, a highly amplified yet somewhat progressive pattern
will dominate the Conus through the period, with a mean trough
across the West and ridging along the Eastern Seaboard. As the next
region of large-scale height falls makes landfall on the Pacific
Coast later today, an upper low spinning over the High Plains this
morning will kick out and evolve into an open wave over the mid-Miss
and Ohio Valleys later today through tonight, pushing the upper
ridge axis to the East Coast, and  exposing the western Carolinas
and northeast GA to a deep/moist SW flow with improving UVVs. This
moisture is expected to begin overspreading the southwest mtns by
evening, with small pops still looking like a good bet by the end of
the day across the Smokies and vicinity. Much lower thickness values
and increasing mid/high clouds will yield substantially cooler max
temps compared to yesterday, but still around 10 degrees above

Pops ramp up to likely/categorical across much of the western 1/4 of
the CWA by midnight or so. With the aforementioned open wave
dampening as it plows into the mean ridge across the East, the best
forcing is expected to a) pass west and north of our forecast area,
and b) weaken as it does so. Additionally, there is some indication
of a Miller-B scenario, with weak Southeast coastal cyclogenesis
developing as the primary surface low weakens across the Ohio
Valley. This will further disrupt low level forcing due to
alterations in the low level flow/thermal advection patterns. Thus,
while most locations in the CWA are likely to see precip tonight,
the southern Appalachians (and points west) are likely to see the
highest qpf, where amounts through 12Z Friday are expected to range
from around an inch across the mtns of SW NC and northeast GA, to
around a half inch across the rest of the NC/SC mtns. Meanwhile, the
remainder of the area is only expected to see around 1/4 inch, give
or take a tenth. Min temps will again be in the neighborhood of
where our highs should be this time of year.


As of 225 AM EST Thursday...The short range begins with a lingering
insitu wedge which will break down rather quickly by the early
afternoon. Some low-end sfc-based instability will be present along
and south of the bndry...but likely not enuf for sigfnt thunder or
deep conv activity. Upper ridging builds in during the day...but
llvl clouds will persist in moist and warm h925-h85 sw/ly flow.
This flow will enabling max temps to reach arnd 10-12 degrees above
normal. Above normal mins Fri night as well with sw/ly flow
continuing and increasing mid/upper clouds ahead of a developing srn
frontal system.

Model differences creep in pretty quickly Sat with a complicated
pattern developing. The frontal bndry to the south comes under the
influence of the Atl ridging and moves north as a warm front. The
ECMWF has a much quicker push into the CWFA then the other op models
bringing measurable precip across the entire FA before 18z. The
other models catch up later in the afternoon...however the GFS,
NAM12, and the CMC have the deep convection aligned across the
Midlands. This srn qpf max agrees fairly well with the going fcst so
will make little changes through 00z Sun. A warm sect atmos will
again keep temps well above normal.

A deep occluded system develops over the TX/OK panhandle late Sat
and upper difl increases greatly through the overnight. This will
generate a sfc wave along the front and begin to swing the whole
system into the FA thru the day Sun. Instability will increase aft
18z to arnd 1500 J/kg...and along with increasing bulk
shear...stg/svr storms are likely during the afternoon. Another
concern will be the amount of rainfall with this system. First with
the warm front...then the moist occluded front crossing Sun night.
The guidance is still unclear and non/supportive with amounts...with
the ECMWF displaying roughly twice the qpf of the GFS and the CMC.
For now the higher amounts...btw 2-3 inches storm total...should
occur across the srn escarpment zones where a few hydro issues could
be realized by Sun afternoon. Another unseasonably warm day Sun with
max temps near 70 non/mtns and low/mid 60s mtn valleys.


As of 155am EST Thursday:  Monday morning through Wednesday night.
Low pressure is forecast to be moving northeast from the Carolinas
on Monday morning with warm high pressure building across our region
for Tuesday and Wednesday. Due to the newest GFS lagging the 500mb
low over Augusta at 12Z Monday, with low instability of under 100
CAPE at 18Z Monday for our CWA. The ECMWF has the low over
Greensboro at 12Z and no instability for our area on Monday. Expect
decreasing coverage of showers across our area on Monday as the low
departs the area. A shallow 500mb ridge transits our region from
west to east Tuesday and Wednesday with surface high pressure
centered near near the Yucatan. A broad 500mb trough with axis from
the Dakotas to Arizona on Wednesday will shift slowly east with the
advancing surface cold front reaching our region early Thursday.
Therefore, expect a cool down for the last half of the week after
the cold front moves off the East Coast and upper trough pushes east
over our area.  Until then, above normal temperatures will prevail
with max temps 5 to 10 degrees above normal Monday and Tuesday then
10 to 15 above Wednesday. Min Temps 10 to 15 degrees above normal.


At KCLT and Elsewhere: VFR conditions are expected through 00Z
Friday, with gradually deteriorating conditions expected to
overspread the area beginning around mid-evening and continuing
through the overnight, as precipitation approaches from the west. In
the interim, light NE winds at the beginning of the period are
expected to become south of east around 18Z, then become southeast
or south this evening. For tonight, categorical -SHRA along with
MVFR conditions are expected to begin at KAVL by 04Z, at KCLT by
09Z, and the other sites in between. A 3 to 4 hour period of PROB30
for -SHRA will precede this time. Guidance depicts IFR or LIFR
conditions developing by the end of the period, but confidence in
timing that into the area is low at this point, so have opted to
leave conditions at the low end of MVFR for the time being.

Outlook: The very unsettled pattern will continue through the
weekend, bringing periods of rain and/or restrictions. Heavy rain
showers and perhaps thunderstorms are possible Sunday.

Confidence Table...

            11-17Z        17-23Z        23-05Z        05-06Z
KCLT       High 100%     High 100%     High 100%     High 100%
KGSP       High 100%     High 100%     High 100%     Med   77%
KAVL       High 100%     High 100%     High 100%     High  87%
KHKY       High 100%     High 100%     High 100%     High 100%
KGMU       High 100%     High 100%     High 100%     Low   48%
KAND       High 100%     High 100%     High 100%     Low   48%

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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