Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 281134
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
734 AM EDT Wed Sep 28 2016

.SYNOPSIS...
A stationary front will remain over the Midlands of South Carolina
and the Sandhills of North Carolina today through Thursday.
Meanwhile, an upper level low will drop south into the Ohio Valley
today and linger there through the end of the week.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 645 AM Wednesday: Main changes for the near-term update have
been to remove pops early this morning and trend back up into the
afternoon forecast. Made some minor adjustments to sky grids and
other aviation-related parameters, with some minor tweaks to
temperature trends through the morning, but no major changes.

Overall synoptic pattern consists of deep closed low over Lake
Michigan, with shortwave axis coming around the base of the trough
as the low continues to dig south toward the Ohio and Tennessee
Valleys during the near term. Cold front currently stalled across
the foothills has kept most of our forecast area in a fairly moist
airmass. Expect very little change to mass fields aloft through the
near term but as the upper low dives south the jet axis will push
this way as well, with the kicking shortwave finally rounding the
base of the upper low toward the end of the period.

For today, with the front inching its way across the area, should
see another surge in temperatures to above-normal levels (so much
for that mid-week cool-down, unless you`re in the mountains that
is). Instability will increase again today and with the synoptic
forcing from the front, PVA from approaching vorticity max, and
continued broad jet-level divergence, convection should be a little
more organized. With the approach of the upper low comes an increase
in deep-layer shear as well, and with sbCAPEs between 1000-2000 J/kg
this afternoon (or upwards of 3000 J/kg if you believe the NAM),
this afternoon should see the best chance of severe convection. That
said, despite the fairly poor lapse rates and lack of deep-layer
shear yesterday, we still had a handful of severe thunderstorms. SPC
Day1 outlook continues with Marginal Risk for areas along and east
of the I-77 corridor but would not be surprised to see a Slight Risk
at some point today. Heavy rain remains a concern with very high
PWs, but with the upper low coming around, should see some mid-level
drying across the area which, while enhancing severe potential, will
help to limit heavy rain potential.

With the passage of the front today, despite the slower trend the
past few days, we should actually see some dry air advecting in
tonight and a resultant drop in overnight lows, generally 5-7
degrees cooler than what we`ll see this morning.

&&

.SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/...
As of 300 AM Wednesday...large upper low will settle around central
KY on Thursday, then wobble around the Ohio Valley Friday. This
position brings a dry slot into the CWFA, but a band of moisture
will linger just east of I-77. With the models trends a little more
west on the position of the low, temps will continue to be above
normal Thursday, and PoPs were cut back in the mountains. Highs
Thursday in the 60s to lower 70s in the mountains, and upper 70s to
mid 80s in the piedmont. Lows will range from 40s in the moutains to
upper 50s east of I-77. Friday still looks like our coolest day, and
should be dry (altho the latest ECWMF keeps the moisture plume
across the I-77 corridor). Temps should be around normal, Friday,
but if model trends continue in later runs, these may get bumped up
further. Highs in the 60s to upper 70s, and lows 40s in the
mountains and lower to mid 50s in the piedmont.

&&

.LONG TERM /SATURDAY THROUGH TUESDAY/...
As of 315 AM EDT Wednesday...the upper low should begin to lift
north and then northeast this weekend from the central Ohio Valley
to somewhere in the eastern Great Lakes by 12Z Monday. Dry
deep-layer SWLY flow will continue to wrap around this circulation
atop the CWFA. At the surface, a nebulous pressure pattern will
exist across most of the area under the lifting upper low. Then the
models show a surface high pressure system build across the Great
Lakes to New England Tuesday and Wednesday, reinforcing dry air from
the north. So expect dry conditions and above normal temps through
the medium range. One interesting thing to watch will be a tropical
cyclone that is expected to develop in the Carribean, then lift
north toward the East Coast next week. At the moment, models are not
in good agreement on this, so confidence on any direct impacts is
very low.

&&

.AVIATION /12Z WEDNESDAY THROUGH SUNDAY/...
At KCLT: Patchy restrictions have developed around the airfield but
none so far at KCLT itself, so will keep the TEMPO MVFR through 13z
and VFR thereafter. Convection is expected to develop again this
afternoon with the cold front still in the vicinity. For the 12z
TAF, have transitioned the PROB30 to TEMPO TSRA, with best timing
between 18-22z, though this may have to be adjusted in later
updates. Winds generally on the S side through the period, lgt/vrb
overnight and increasing to between 5-10kt this afternoon.

Elsewhere: IFR to VLIFR restrictions continue for most of the TAF
sites this morning, but should see rapid clearing shortly after TAF
issuance for all but possibly KAVL with lingering valley fog.
Convection chances not high enough to include anywhere, with the
exception of VCSH at KHKY this afternoon. Guidance hinting at
another round of vsby restrictions at KAVL/KHKY, with possible cigs,
Thursday morning and have trended that way introducing MVFR late in
the period. Wind trends similar to KCLT except mainly up-valley at
KAVL.

Outlook: Dry high pressure will build in slowly behind the front
into Thursday, which should bring VFR conditions in most places
through the end of the week, although some instability could lead to
showers over the NC part of the area on Thursday afternoon.

Confidence Table...

            11-17Z        17-23Z        23-05Z        05-06Z
KCLT       High  94%     High 100%     High 100%     High 100%
KGSP       High 100%     High 100%     High 100%     High 100%
KAVL       Med   61%     High 100%     High 100%     High 100%
KHKY       High  83%     High  95%     High 100%     High 100%
KGMU       High  83%     High 100%     High 100%     High 100%
KAND       High  83%     High 100%     High 100%     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:

www.weather.gov/gsp/aviation

&&

.GSP WATCHES/WARNINGS/ADVISORIES...
GA...None.
NC...None.
SC...None.

&&

$$
SYNOPSIS...ARK
NEAR TERM...TDP
SHORT TERM...ARK
LONG TERM...ARK
AVIATION...TDP



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