Area Forecast Discussion
Issued by NWS Greer, SC

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000
FXUS62 KGSP 240214
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
1014 PM EDT TUE AUG 23 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 in the
front`s wake. Rain chances will remain below normal through the
weekend, with maximum temperatures above average through early next
week.

&&

.NEAR TERM /THROUGH WEDNESDAY/...
As of 1005 pm: Latest satellite images indicated a gradual expansion
of mid level clouds across the Lakelands this evening with a band of
high clouds pushing east out of TN. NAM continues to look too wet
during the overnight hours. I will update the forecast to adjust sky
and temps with the latest observations, then adjust trends into the
late night hours. Overall, the current forecast appears on track.

At 730 PM, recent IR and dimming visible satellite images indicate
FEW to SCT mid and high clouds across the forecast area. A large
area of cloud cover was located over southern GA with a thick band
over middle TN. NAM appears too moist with overactive convective
parameterization across the Smokies. As a result, the solution
appears to have too much low level moisture across the forecast area
late tonight. The GFS appear to be the better solution, pivoting a
band of cloud cover across the southern Appalachians and upper
Savannah River Valley late tonight into Wednesday morning. Any
morning low clouds should mix and lift to fair weather CU by mid to
late morning. Weak sct showers will be possible across the mtns
tomorrow after sunrise, I will increase ridgetop PoP to chc. Winds
may remain from the ENE through 1z, then winds should favor a
direction from the ESE tonight, and SSW Wed afternoon, speeds 6 kts
or less.

As of 150 PM: The CWFA remains under an easterly flow regime
associated with sfc high pressure centered over the Chesapeake Bay
region. A strong subsidence inversion was evident from the 12z KGSO
sounding, and as expected this is keeping deep convection suppressed
over most of the area. The inversion is substantially weaker to
our south and west, however, and a few showers have occurred over
NE GA since late morning. This activity may continue to percolate
thru the heat of the aftn, but RAP profiles suggest the inversion
strengthens rapidly going north and east, and is likely too strong
to overcome beyond the Savannah River counties of SC.

Tonight looks like it will play out similarly to last night, with
a weak southeasterly flow developing some patchy stratocu toward
daybreak. The NAM, which verified reasonably well w.r.t. cloud cover
this morning, depicts moisture being even deeper Wed morning, so
cloud cover is expected to be more widespread. Some fog is expected
in the mountain valleys, especially if/where cloud cover does not
develop. Min temps should be a little warmer in the presence of
modified air and more cloud cover.

As the high slips further offshore, the subsidence inversion will
weaken; we`ll continue to see moisture rebound. Accordingly
a consensus of various model guidance supports a return of
mentionable PoPs over the mountains. Further east lapse rates
remain just too weak. No appreciable threat of severe weather
exists given modest wind and moisture profiles. Lent slightly
more weight to bias-corrected temps given that we will again see
elevated dewpoints; this supports max temps rising a degree or
two above Tuesday`s values.

&&

.SHORT TERM /WEDNESDAY NIGHT THROUGH FRIDAY NIGHT/...
As of 215 PM EDT Tuesday...it looks like the Southeast will be
dominated by a mid/upper level anticyclone through the late part of
the week. This will support surface high pressure ridging back from
off the east coast on Thursday and will keep a weak cold front at
bay to our N on Friday. The models suggest low level moisture, which
is unimpressive to begin with, should mix out each day. This will be
a limiting factor and should preclude any deep convection east of
the Blue Ridge through the period. Across the mountains, we should
be able to generate a few showers both days and the fcst might be
overly-optimistic with patches of 30 pct in the afternoon. The
chances of anything significant are small. Temps will be close to
normal on Thursday and then maybe a category or so above normal
Friday.

&&

.LONG TERM /SATURDAY THROUGH TUESDAY/...
As of 230 PM EDT Tuesday...the extended period begins 12Z Saturday
morning with the southeast still under the influence of a
substantial upper ridge, with a surface high moving over the
northeastern CONUS. This will keep max temperatures across the
entire forecast area well above average, and precip chances well
below average for the weekend. The ridge will be relatively slow to
erode, so the only sensible pops will be confined to the higher
terrain through the weekend and early next week. By late Monday,
though, guidance does suggest modest height falls may start to
occur, so the forecast features a slight decrease in max temps to
just a degree or two above average by Tuesday. Guidance diverges
significantly after that, however, with the GFS increasing moisture
early next week as another frontal boundary approaches the southern
Appalachians (no tropical low to speak of), and the ECMWF
maintaining the development of a tropical low in the Bahamas/Gulf of
Mexico. Development of the system is uncertain at best right now,
and this model divergence currently has little impact over the
forecast through next Tuesday, so model trends will simply be
watched over the next few cycles. Overall, there were few sensible
weather changes from the previous guidance package.

&&

.AVIATION /02Z WEDNESDAY THROUGH SUNDAY/...
At KCLT and elsewhere: At 730 PM, recent IR and dimming visible
satellite images indicate FEW to SCT mid and high clouds across the
forecast area. A large area of cloud cover was located over southern
GA with a thick band over middle TN. NAM appears too moist with
overactive convective parameterization across the Smokies. As a
result, the solution appears to have too much low level moisture
across the forecast area late tonight. The GFS appear to be the
better solution, pivoting a band of cloud cover across the southern
Appalachians and upper Savannah River Valley late tonight into
Wednesday morning. I will indicate periods of low clouds across KAVL
and KAND, with a TEMPO at KGSP and KGMU. Any morning low clouds
should mix and lift to fair weather CU by mid to late morning. Weak
sct showers will be possible across the mtns tomorrow after sunrise,
I will increase ridgetop PoP to chc. Winds may remain from the ENE
through 1z, then winds should favor a direction from the ESE
tonight, and SSW Wed afternoon, speeds 6 kts or less.

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...

            02-08Z        08-14Z        14-20Z        20-00Z
KCLT       High 100%     High 100%     High 100%     High 100%
KGSP       High 100%     High  97%     High 100%     High 100%
KAVL       High  88%     Med   77%     High  95%     Med   68%
KHKY       High  88%     High  83%     High 100%     High 100%
KGMU       High 100%     High  97%     High 100%     High 100%
KAND       High  88%     High  91%     High  93%     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...LEV
NEAR TERM...NED/Wimberley
SHORT TERM...PM
LONG TERM...LEV
AVIATION...NED



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