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Area Forecast Discussion

366
FXUS62 KGSP 240731
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
331 AM EDT WED AUG 24 2016

.SYNOPSIS...
High pressure will persist over the region through midweek allowing
temperatures to climb back above normal. Another weak cold front will
approach the Western Carolinas from the northwest toward the end of
the work week, with high pressure building back to our north over the
weekend.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 300 AM EDT...A large upper 596 dam high at 500 mb will
continue to dominate the Southeast, keeping a subsidence inversion
in place atop most of the CWFA. As the high builds slightly, it will
push a plume of higher RH in from the west. This axis will be across
the western third or so of the CWFA this afternoon. So within that
moisture, a better chance of afternoon convection is expected. The
model consensus is for isolated to scattered showers with a few
embedded garden-variety tstms, as CAPE and shear will be marginal.
The 00z NAM was thrown out for this forecast, however, due to
grid-scale  convective feedback over the southern NC mountains.
Steering flow will be out the north, and will try to carry this
activity into the Upper Savannah Valley, which should be modestly
unstable (SBCAPE around 1000 J/kg). So will go with consensus chance
PoPs in the mountains and the Upper Savannah Valley. Temps will be
similar to yesterday`s readings.

Tonight...Anyway showers and/or storms that do develop should
dissipate quickly with loss of heating this evening. However,
deep-layer moisture will linger atop the CWFA, which will keep skies
partly to mostly cloudy overnight. The 850 mb flow will shift from
SELY to NWLY as the low-level high pres shifts westward slightly. So
instead of stratocu from upslope flow, perhaps more mid and high
cloudiness. Temps will bottom out at or slightly above normal.

&&

.SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/...
As of 315 AM EDT Wednesday...the short term fcst picks up at 12Z
on Thursday with broad upper ridging in place over the SE CONUS
that will persist well into the medium range. At the sfc, high
pressure will move farther NE of our area on Thursday allowing the
wedge to weaken and essentially dissolve. An area of pre-frontal
moisture will pass to our north later on Thursday and into Friday,
yet the model guidance has been trending a bit drier since yesterday
and keeps most of the deeper moisture out of the CWFA. As the front
lifts farther NE late Friday and into Saturday, another high slides
over the Great Lakes in its wake. As for the sensible wx, the models
have been trending a bit drier overall but still have more moisture
over the higher terrain especially on Thursday. Temps start out around
climatology if not just above, and warm thru the period with highs on
Friday and Saturday about a category above normal.

&&

.LONG TERM /SATURDAY THROUGH TUESDAY/...
As of 3 AM EDT Wednesday...the medium range fcst picks up at 12Z
on Saturday with broad upper ridging in place over the SE region.
The ridge is expected to flatten a bit on Sunday and Monday but
still maintain control over the overall synoptic pattern. It is
noteworthy that the 12Z run of the ECMWF continues to develop a
tropical low over the Bahamas early in the period and move the
low due west across Southern Florida and then north over the
northern gulf coast by day 7. The newer 00Z run of the GFS also
tries to develop a low over the same area, but it remains considerably
weaker at this time. At the sfc, high pressure will be centered to
our north over the Great Lakes keeping things mostly dry for the
weekend and early next week. The big question comes just beyond
day 7 and the possibility of a tropical system moving into the
Gulf of Mexico and making landfall along the northern gulf coast.
It is still too early to have much confidence in any specific
model track, but it`s looking like a tropical low will develop
during that timeframe. As for the sensible fcst, no major changes
were necessary with below climo POPs for the period and temps about a
category above normal.

&&

.AVIATION /08Z WEDNESDAY THROUGH SUNDAY/...
At KCLT...Similar setup to yesterday, with high pressure over the
Mid-Atlantic bringing the winds around out of the SE, then veering
further to S. VFR conditions are expected, despite a relatively
moist S/SE low-level flow. Some MVFR stratus is expected to develop
across the Upstate west of KCLT, but not affect the terminal.
Otherwise, patchy stratocumulus around 5000 to 6000 ft bases on and
off through the period.

Elsewhere...The 00z NAM suffered from grid-scale convective
feedback, dumping a blob of heavy rain over the southern NC
mountains. This affects all NAM-based guidance, so it had to be
thrown out. So with mainly just GFS-based guidance to work with,
this is a slightly below normal confidence forecast. Still, I think
the GFS is handling the setup well, developing some MVFR
stratocumulus within SELY flow toward daybreak across the Upstate
and into the NC mountains. Will go with a few hours of MVFR at the
Upstate sites. At KAVL...confidence is the lowest. Assuming periods
of high-based cumulus develop, I don`t think there will be much fog
in the French Broad Valley. That said, the dew points are running
several degrees higher than this time last night. So I will keep the
TEMPO for IFR CIGS and MVFR VIS. It`s also possible the
aforementioned MVFR clouds may reach the site around daybreak with
help from SELY upslope flow. Later today, guidance agrees on a
little more moisture for afternoon convection in the NC mountains.
Still not quite high enough PoPs to warrant a PROB30 at KAVL, but
one may be added with a later TAF update. Winds will be light at all
sites through the period.

Outlook: A deep ridge will remain in place over the Southeast thru
the weekend, keeping afternoon SHRA/TSRA chances below normal each
day, and generally confined to the mountains. However, sfc moisture
will gradually return, and morning vsby restrictions will become
increasingly likely during this time.

Confidence Table...

            07-13Z        13-19Z        19-01Z        01-06Z
KCLT       High 100%     High 100%     High 100%     High 100%
KGSP       High  85%     High  83%     High 100%     High 100%
KAVL       Med   78%     Med   75%     High  96%     High  96%
KHKY       High  96%     High  92%     High 100%     High 100%
KGMU       High  88%     High  84%     High 100%     High 100%
KAND       High  84%     Med   75%     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...JPT
NEAR TERM...ARK
SHORT TERM...JPT
LONG TERM...JPT
AVIATION...ARK



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