Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 201724
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
124 PM EDT Sun Aug 20 2017

.SYNOPSIS...
Relatively dry High pressure will give way to a warming and
moistening airmass early in the first half of the week. This will
give our region hot and humid conditions ahead of an approaching
cold front which will reach our area Wednesday night or early
Thursday. Expect cooler and drier air from Thursday through next
weekend.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 1030 AM EDT Sunday: Grids look good this morning, but have
reduced sky cover and updated temperature trends through the morning
and early afternoon hours. Overall MaxT not really adjusted. Hi-res
guidance indicating possibly slightly higher coverage of convection
(mainly showers) across the mountains today but without even any Cu
forming yet, hard to justify making many changes to pops since
overall coverage will still be isolated. Will continue to monitor
through the morning.

Otherwise, heights will rise through the near term, as upper trough
progresses off the East Coast and the subtropical ridge increases
its influence on the Southeast. Resultant warmer temperatures as
well as increasing boundary layer moisture due to a transition to
more of a SE flow should yield improved instability across our area
this afternoon. However, mid-level lapse rates will remain very
poor, owing in part to a pronounced stable layer based at around
700mb as depicted in forecast soundings. Nevertheless, the improved
instability does allow some spotty convection to develop along the
ridge tops in most high resolution guidance, so slight chances for
deep convection will be advertised there. Max temps will generally
be a solid category above climo. Warm and increasingly muggy
conditions will be felt tonight, as low level moisture continues
increasing on SE flow.

&&

.SHORT TERM /MONDAY THROUGH TUESDAY/...
As of 3:00am EDT Sunday:  Short-term forecast is dominated by
presence of a Bermuda high extending westward across the Southeast.
On Monday, surface anticyclone with this high over the Atlantic
produces a little southeasterly flow than will help moisture with
the GFS indicating some showers in upslope areas of the Southern
Appalachia Monday afternoon. Winds will continue generally light,
and this anticyclone will only advance dewpoints a few degrees,
but flow into the mountains may help initiate some showers.
Cloudiness on Monday for eclipse time are still not too bad at 30 to
40% (near climo).  Mountainous areas look to  have a greater chance
for clouds given the weak upslope moisture flow.  MLCAPE does
increase to the marginal level on Monday and Tuesday afternoons,
with lower amounts over the mountains where initiation is more
likely.

On Tuesday, situation does not change a whole lot with 500mb heights
declining a slight 2 dam as Eastern CONUS pattern becomes slightly
more trough-oriented, and Bermuda high moves a little eastward,
making surface winds more southwesterly and keeping some chance for
Tuesday afternoon showers, primarily over the mountains.

With only subtle changes to the airmass, conditions will remain hot
and sticky through Tuesday.

&&

.LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/...
As of 3:30am EDT Sunday: EC and GFS models maintain some agreement
through the extended forecast as they both have an eastern CONUS
upper trough with a cold front and enhanced chances for rain by
Wednesday evening, followed by cold FROPA on Thursday and drier
subsequent conditions; though details differ quite a bit with the EC
having a somewhat deeper trough. Models generally agree on higher
POPs with a FROPA in the Wed.-Thu. time frame, with a substantial
drop-off in dewpoints and highs dropping below climo Thurs. through
Sunday.

Per the GFS, MLCAPE levels remain subdued to moderate in the 400 to
1200 j/kg range through Thursday with moisture being scoured behind
the front and much reduced chances for thunder Friday and Saturday.

&&

.AVIATION /18Z SUNDAY THROUGH FRIDAY/...
At KCLT and elsewhere: Low VFR Cu expected this afternoon
and again toward the end of the period. Increasing low-level
moisture through the period as flow swings around to the SE will
allow for some VFR to possibly MVFR fog to develop in the Piedmont
by Monday morning, in addition to improved conditions for the
typical mountain valley fog/low stratus that should affect KAVL
overnight. ENE winds will veer ESE this afternoon, back to ENE by
early Monday morning, then veering again SE by the end of the
period. Convection this afternoon will remain limited to the
mountains and not high enough to include at KAVL. Could see
additional mountain convection tomorrow, but not until after the end
of the period.

Outlook: Chances for diurnal convection and morning mtn valley
fog/low stratus gradually increase during through mid week, with the
best chances expected Wednesday, as a cold front pushes into the
area. Chances for restrictions and diurnal convection may diminish
again during late week.

Confidence Table...

            17-23Z        23-05Z        05-11Z        11-12Z
KCLT       High 100%     High 100%     High 100%     High  83%
KGSP       High 100%     High 100%     High 100%     High  83%
KAVL       High 100%     High 100%     High  83%     High  94%
KHKY       High 100%     High 100%     High 100%     High  83%
KGMU       High 100%     High 100%     High 100%     High 100%
KAND       High 100%     High 100%     High 100%     High  83%

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...DEO
NEAR TERM...JDL/TDP
SHORT TERM...WJM
LONG TERM...WJM
AVIATION...TDP



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