Area Forecast Discussion
Issued by NWS Greer, SC

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000
FXUS62 KGSP 201448
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
1048 AM EDT Sun Aug 20 2017

.SYNOPSIS...
Relatively dry High pressure will give way to a warming and
moistening airmass early in the new work week, bringing hot and
humid afternoons Monday through Wednesday. A cold front is expected
to pass through Wednesday night and usher in cooler and drier air
that will last into 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 /15Z SUNDAY THROUGH THURSDAY/...
At KCLT and elsewhere: Only change to the KCLT TAF for the 15z
AMD is to add FEW040 to the prevailing group as low VFR clouds
should begin forming soon. Otherwise, VFR conditions are expected to
persist through at least the evening hours. Chances for high terrain
convection will be slightly improved today vs. yesterday, but
coverage will be very sparse and no mention of convection is
warranted at any of the terminals this afternoon/ evening.
Otherwise, light N to NE winds should turn south of due east this
afternoon. Improved chances for fog/low stratus are anticipated
tonight, particularly in the mtn valleys, and MVFR visby is forecast
at KAVL by 09Z, although conditions certainly could prove to be more
restrictive.

Outlook: Chances for diurnal convection and morning mtn valley
fog/low stratus gradually increase during early-to-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...

            14-20Z        20-02Z        02-08Z        08-12Z
KCLT       High 100%     High 100%     High 100%     High  95%
KGSP       High 100%     High 100%     High 100%     High  95%
KAVL       High 100%     High 100%     High 100%     High  82%
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  95%

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



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