Area Forecast Discussion
Issued by NWS Greer, SC

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947
FXUS62 KGSP 270616
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
216 AM EDT SAT AUG 27 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 TODAY/...
As of 215 AM: The center of 595 DM ridge will lift over the DELMARVA
region as a western Atlantic mid level low drifts slowly toward the
Carolina coast today. Broad high pressure will remain across the
Great Lakes region, ridging south across the forecast area. This
pattern should provide SKC to FEW sky cover through the morning
hours. Winds are forecast to rise to 6 to 8 kts from the ESE during
the daylight hours. The forecast for SHRA and TSRA will be a
challenge this afternoon and evening. It appears that a region of
mid level Q-Vector convergence will develop between the H5 ridge and
low, generally over the I-85 corridor. The llvl ESE flow should
transport a weak sea breeze inland across the Midlands to eastern
Piedmont. CAPE values west of the sea breeze should generally range
in the moderate range with low values of CIN. The combination of the
weak mid level forcing and weak llvl boundary should trigger SCT
SHRA/TSRA this afternoon, tracking from NE to SW.

As of 1035 PM EDT Friday:  Surface convergence along a lingering
lee trof combined with a small region of nearly 1.5-2.0 j/kg
mucape seems to be enough to allow for sustainment of the one
solitary storm in the cwa.  Said storm is somewhat vigorous
as low/mid level velocities were enough to warrant a sps over
the last few volume scans.  That said, latest spc meso analysis
does favor propagation into a less favorable dcape environment
as the storms slides westward into northeast GA.  Therefore,
wouldn`t be suprised if it did survive for another hour or so
before diminishing, however any downburst wind threats should
decline shortly.  As for the fcst, adjusted pops to account
for this storm as well as the lack of any other convection.
Also tweaked t/td/sky to account for recent obs/irsat analysis.
No other sig changes needed/made with this update.

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 /TONIGHT 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 /06Z SATURDAY THROUGH WEDNESDAY/...
At KCLT and elsewhere: The center of 595 DM ridge will lift over the DELMARVA
region as a western Atlantic mid level low drifts slowly toward the
Carolina coast today. Broad high pressure will remain across the
Great Lakes region, ridging south across the forecast area. This
pattern should provide SKC to FEW sky cover through the morning
hours. Winds are forecast to rise to 6 to 8 kts from the ESE during
the daylight hours. The forecast for SHRA and TSRA will be a
challenge this afternoon and evening. It appears that a region of
mid level Q-Vector convergence will develop between the H5 ridge and
low, generally over the I-85 corridor. The llvl ESE flow should
transport a weak sea breeze inland across the Midlands to eastern
Piedmont. CAPE values west of the sea breeze should generally range
in the moderate range with low values of CIN. The combination of the
weak mid level forcing and weak llvl boundary should trigger SCT
SHRA/TSRA this afternoon, tracking from NE to SW. I will highlight
the most likely period of convection with a PROB30. Otherwise, sky
conditions should favor SCT045-050 CU. However, KAVL could see a
period of LIFR ceiling this morning around sunrise, KAND may see
MVFR fog between 11z to 13z.

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 within two hours following sunset.
Patchy fog will be possible any morning following a late afternoon
to early evening shower or thunderstorm.

Confidence Table...

            06-12Z        12-18Z        18-24Z        00-06Z
KCLT       High 100%     High 100%     High 100%     High 100%
KGSP       High 100%     High 100%     High 100%     High 100%
KAVL       High  83%     High  94%     High 100%     High  80%
KHKY       High  86%     High  94%     High 100%     High  90%
KGMU       High 100%     High 100%     High 100%     High 100%
KAND       High 100%     High  93%     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...NED
SHORT TERM...HG
LONG TERM...LEV
AVIATION...NED



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