Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 250242

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
1042 PM EDT WED AUG 24 2016

High pressure will persist over the region for the next few days,
allowing temperatures to climb back above normal. Another weak
surface 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. Rain chances will remain below normal
through the beginning of next week. Another front will approach the
area by the middle of the next work week.


As of 1030 PM EDT Wednesday:  Low stratocu has lifted across the
vast majority of the fcst are this evening leading to only a few
mid/high clouds.  Winds remain light and out of the wnw, with
a few piedmont and fthill sites already calming.  Otherwise,
guidance continues to favor patchy fog about the region by
daybreak, the most dense of which being in the mtn valleys where
xover temperatures are most threatened.  Elsewhere, wouldn`t be
all that suprised to see some patchy fog around the Lakelands as
well as the I40 corridor region of the NC piedmont.  Went ahead
and removed all pops for the evening, as well as making tweaks
to t/td and sky once again to align with recent obs/sat trends.
No other sig changes needed/made with this late evening update.

Previous Discussion: The pattern remains largely the same tonight,
with low level winds veering in response to a trough moving thru
the northeastern CONUS, but still generating weak isentropic lift
and bearing a fair amount of moisture. Patchy midlevel clouds
thus are expected to persist, albeit not as uniform as what we
experienced this morning. Guidance consensus develops fog in
the mountain valleys and portions of the foothills before dawn,
which in light of limited mixing today is plausible as long as
the cloud decks remain broken. Min temps should be a tad above
climo. For tomorrow, I was a little reluctant to really clear skies
out quickly seeing how it developed this morning, seeing as the
pattern will have changed so little. One difference is that winds
will be more downslope, which could help speed erosion. Once again
the mountains are expected to destabilize sufficiently to expect
scattered convection, with the Piedmont still seeing the limiting
effect of subsidence within the ridge airmass. So PoPs are limited
to the high terrain. Max temps are expected to be near climo,
a bit warmer than today with the expectation of less cloudiness.


As of 215 PM EDT Wednesday...the late part of the week still looks
relatively quiet as a mid/upper anticyclone/ridge moves overhead on
Friday. This should keep some warmer air aloft and convective
inhibition that will help to put a damper on the amount of deep
convection. Thus, have limited the precip probability to the low end
of the chance range and only over the higher terrain. Temps will
climb back above normal. Starting on Saturday, uncertainty ramps up
with regard to the effect of the anticyclone center moving off to
the east and the position of a weak front drifting down from the N.
The operational GFS is more responsive than the other models,
perhaps because of a stronger SE flow at low levels which brings in
Atlantic moisture, while the operational NAM might be too dry
because it drives the surface boundary to our S and actually has a
wedge-like configuration by late afternoon. The official forecast
still favors the higher terrain with a slightly below climo chance
of precip, but allows for isolated storms to move out across the
I-40 corridor in the afternoon and the rest of the Piedmont/Upstate
in the evening. Not sure yet how this will trend, but still expect
precip chances to be diurnal in nature. Temps will depend on the
ability of the shallow surface boundary to slip southward. The
chance for severe storms looks low.


As of 230 PM EDT Wednesday...the extended forecast begins 12Z Sunday
with a large upper ridge over the southeast beginning to flatten.
Model guidance diverges almost immediately with the handling of this
ridge and subsequent features, so the forecast consists of a multi-
model blend that is weighted towards the ECMWF, which has displayed
better run-to-run consistency than the rest of the global model
suite over the past few days. The upper ridge does maintain a
warming and drying influence over the southern Appalachians into
early next week, though it begins to decay somewhat Sunday and
Monday. Pops were therefore kept below climo through early next
week, and maximum temperatures were kept a few degrees above climo.
A surface frontal boundary will begin to approach the area next
Tuesday, though its timing and the amount of moisture it has to work
with are dependent on the track and intensity of a potential
tropical system that is being investigated by the National Hurricane
Center. Most models now show some development of the system, and
though the tracks of the system in the major models are currently
quite different, it appears that no direct impact from it will occur
in our area through the next seven days. The ECMWF allows for more
moisture return into the southeast, so pops were elevated to
near/just above climo by the middle of next week. Overall, little
change was made to the previous medium range forecast, especially
considering the large amount of uncertainty in global model
solutions at the current time.


At KCLT and elsewhere:  VFR through the period at all sites aside
for possible fog induced visb/cig restrictions at a KHKY/KAVL and
possibly KAND where xover temps are fcst.  Otherwise, high pressure
will keep conditions relatively quiet with all tafs dry aside for
KAVL where mtn convection is possible on Thursday afternoon.  Thus,
favored mid/high cirrus overnight at all sites aside for the above
mentioned restricted sites where ifr/lifr stratus is possible.
Beyond that, a moist BL will prevail allowing for development of low
vfr cu for the afternoon hours.  Winds will be a bit vrb initially,
calming overnight, then increasing out of the wsw into late

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%     Med   70%     High 100%     High 100%
KAVL       High  95%     Med   79%     High  95%     High 100%
KHKY       High  95%     High  91%     High 100%     High 100%
KGMU       High 100%     Med   70%     High 100%     High 100%
KAND       High 100%     Med   79%     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:




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