Area Forecast Discussion
Issued by NWS Greer, SC

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852
FXUS62 KGSP 262101
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
501 PM EDT FRI AUG 26 2016

.SYNOPSIS...
Surface high pressure will build over the region through the
weekend. Tropical low pressure will slowly strengthen off the
southern tip of Florida early next week and then possibly move into
the Gulf of Mexico. Forecast uncertainty is very high with this
system.

&&

.NEAR TERM /THROUGH SATURDAY/...
As of 500 PM EDT Friday:  Continuing to monitor convection tracking
along/south of the I85 corridor this afternoon where max diff
heating has occurred allowing for elevated instability levels
coincident with the weakest CIN associated with the northeast
sfc ridge.  Dcapes in the region remain high, generally 1200j/kg,
thus favoring downburst winds as any primary severe threat.
Latest CamGuide continues with the current convection over the
next hour/two before heating starts to subside leading to downward
trends in coverage.  Adjusted pops up associated with the most
recent coverage.  Also tweaked t/td in the immediate near term to
reflect the most recent ob trends.

At 200 PM Friday: An upper ridge will drift northeast from the
Southern Appalachians to VA by Saturday. The models show weak
surface troughing persisting east of the mountains, while low level
moisture persist across our area. Moderate instability combined with
light upslope flow into the blue ridge will support convection each
afternoon, mainly along the Blue Ridge, however shear appears to
weak for organized convection. Steering flow should be sufficient
to keep cells moving, and unless some training occurs, rainfall
should be limited. Temperatures are expected to run slightly above
normal under the upper ridge.

&&

.SHORT TERM /SATURDAY NIGHT THROUGH MONDAY/...
As of 200 PM EDT Friday: A dominant 500 mb ridge will remain
centered over the mid Atlantic region Saturday night through Sunday.
An inverted wave over the Atlantic offshore waters is expected to
slip westward under the ridge through the day on Sunday, but with
little attendant moisture increase across the Carolinas and NE GA.
With surface high pressure centered northeast of region, low level
northeasterly winds should bring slightly drier dewpoint air into
the NC foothills and piedmont - with an attendant decrease in
convective potential in those areas. Isolated to scattered
convection should continue to develop in easterly upslope flow
farther SW and over the mountains.

The retrograding offshore upper vorticity maximum should stall out
near the SC/GA coast on Monday - with limited westward penetration
of deeper moisture. The easterly upslope flow will continue but with
instability remaining rather unimpressive. Easterly deep layer
steering winds will also continue to take any Blue Ridge development
westward through the period to help curtail piedmont PoPs. Mins will
remain well above climo through the period, with maxes slightly
above.

&&

.LONG TERM /MONDAY NIGHT THROUGH FRIDAY/...
As of 230 PM EDT Friday...The medium range picks up 00Z Tuesday with
a relatively flat pattern aloft. Ridging builds in quickly over the
southern plains early next week, with an upper trough and modest
height falls over the east coast slowly developing. Despite the
deepening trough, the upper ridge axis is close enough to us that
the CWA will encounter some convective suppression with little
moisture return at the surface, so pops were kept well below climo
for the entire area. A surface front will sag into the southern
Appalachians from the north later next week, though models diverge
again on the timing of the frontal passage. No major model is overly
excited about QPF response associated with the front, though, so
precip chances were kept low through the end of next week. Though
there is considerable uncertainty about the depth of an approaching
upper level trough next week, the general trend of lowering maximum
temperatures to just above climo by the end of the next work week
seems reasonable, and was reflected in the forecast.

Now for the largest source of uncertainty in the extended period.
The potential tropical system (currently more of an open wave) is
still disorganized as it approaches the Bahamas, and does not look
to have favorable development prospects for the next couple of days.
Model guidance still features large disagreements as far as track
and intensity, though recent trends suggest a slower track into the
eastern Gulf of Mexico and a weaker system (if it is able to develop
at all, which is a big "if" at this point). The system is not
totally down and out, but impacts from it in our area look
nonexistent at this time, so the trend of lowering pops next week
was continued with this afternoon forecast package. Few other
changes were made to the medium range forecast.

&&

.AVIATION /21Z FRIDAY THROUGH WEDNESDAY/...
At KCLT: VFR. A small chance of convection exists this afternoon,
while winds veer from NE to SE. Cigs are generally no expected,
although low VFR could briefly occur, especially if convection
occurs.

Elsewhere: Daybreak vsby restrictions are expected at all sites but
KGSP/KGMU, with IFR at KAVL and MVFR at KHKY and KAND. Although cig
restrictions are not expected, KAVL had the best chances, with low
valley cloud heights as in the past several days. Winds will veer
from N at KAVL and NE at foothills sites to SE this afternoon, going
light and variable this afternoon, then E to SE on Saturday morning.
Convective chances this afternoon are best at KAVl and KAND, with
KGMU/KGSP a close call.

Outlook: A deep ridge of high pressure will persist across the
region through early next week. The environment should support mid
to late afternoon thunderstorms each day, primarily over the mtns and
adjacent foothills. Weak steering flow should favor iso to sct
coverage, with storms dissipating with two hours following sunset.
Patchy fog will be possible any morning following a late afternoon
to early evening shower or thunderstorm.

Confidence Table...

            21-03z        03-09Z        09-15Z        15-18Z
KCLT       High 100%     High 100%     High 100%     High 100%
KGSP       High 100%     High 100%     High 100%     High 100%
KAVL       Low   55%     Low   55%     Low   55%     Low   57%
KHKY       High 100%     High 100%     High  91%     High 100%
KGMU       High 100%     High 100%     High 100%     High 100%
KAND       High 100%     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...HG
NEAR TERM...CDG/JAT
SHORT TERM...HG
LONG TERM...LEV
AVIATION...JAT



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