Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 191748

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
1248 PM 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 1245 PM: forecast appears to be in decent shape.  Still seeing
cloudiness topping ridge axis, which has moved into western zones,
and then dissipating on the downhill side. The ridge axis should
translate eastward thru the afternoon, thus bringing more cloud
cover in from the west for the rest of the day.

Otherwise...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 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 climo.

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 into the early
part of the evening, with gradually deteriorating conditions
expected to overspread the area from the west beginning late evening
and continuing through the overnight. Wind in the process of
switching from light NE to something more south of east, so think
KCLT will have a southeast wind by 21Z at the latest. The new model
guidance imposes a slight delay in the arrival of the precipitation
from the west, and thus the arrival of the restrictions are also
delayed by another hour or two. See no reason to think that precip
will not eventually move in from the W/SW, as low/mid level forcing
an moisture look excellent. Some of the guidance continues to be
pessimistic and depicts IFR or LIFR conditions developing by the
start of operations on Friday morning, but confidence in that
scenario still low at this point. Prefer to keep most TAFs MVFR as
the precip moves through, and then allow the precip to bring the
ceiling down to IFR and have that condition linger thru mid-morning.
Ceiling should lift back to MVFR in the 15Z to 16Z time frame, but
it may scatter out right around that time as well. so have opted to
leave conditions at the low end of MVFR for the time being. Wind
should veer more to the S overnight, and then SW late in the period.

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...

            17-23Z        23-05Z        05-11Z        11-12Z
KCLT       High 100%     High 100%     High 100%     High 100%
KGSP       High 100%     High 100%     High 100%     High 100%
KAVL       High 100%     High 100%     High  90%     High  87%
KHKY       High 100%     High 100%     High 100%     High 100%
KGMU       High 100%     High 100%     High  83%     High 100%
KAND       High 100%     High 100%     Med   73%     High 100%

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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