Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 191449
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
1049 AM EDT Tue Sep 19 2017

.SYNOPSIS...
A weak trough of low pressure will cross the region from the west
through Wednesday. High pressure will then return from the north
Thursday through Friday, but with more moisture in easterly flow.
Drier and stronger high pressure will settle over the region through
the weekend as both Hurricane Jose and Hurricane Maria remain well
offshore in the western Atlantic.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 1030 AM: Deep layer ridging will highlight the pattern
once again today as an upper ridge axis remains draped along the
Appalachians, and surface high pressure stretches southward from
New England into the southeast.  Meanwhile, Hurricane Jose remains
over the Atlantic, more or less due east of Virginia Beach. Today
looks very similar to days past as far as sensible weather goes, yet
with improved chances for ridgetop convection given slightly lower
upper heights and improved instability through the profile. PoPs
have been revised by blending in some of the latest HRRR, which
does depict a few tiny showers developing in the cloudy area over
the Upstate, but still indicates ridgetop showers breaking out
in the early aftn. (A couple of brief echoes already have shown
up on KGSP over the Upstate.) A couple updrafts may grow into
thunderstorms, but being nonsevere with lightning and gusty winds
being the primary threats since convection will be rather shallow.
Temperatures today will remain above normal levels, however probably
a degree or two cooler than days past given expected abundance of
fair wx cu this afternoon.  Tonight looks to be a repeat of recent
nights given slow erosion of daytime/evening cu/stratocu and the
potential for patchy radiation fog for some locales.

&&

.SHORT TERM /WEDNESDAY THROUGH WEDNESDAY NIGHT/...
As of 300 AM EDT Tuesday: A mid-level trough will cross the
Appalachians from the west on Wednesday. Slightly improved moisture
is evident in model profiles along and east of the trough axis, and
this will raise shower chances. Also anticipate 850 to 500 mb lapse
rates steepening up a bit above 6.5 deg C/km by Wednesday afternoon
to warrant an isolated to scattered thunder mention. Warm maximum
temperatures should reach 5 to 8 degrees above normal Wed.
afternoon.

The trough axis will settle southeast of the forecast area toward
the southeast coastline on Thursday, with drier air settling into
our region from the northwest. Warm conditions will continue, but
with temperatures perhaps a degree below Wed. values.

&&

.LONG TERM /THURSDAY THROUGH MONDAY/...
As of 300 AM EDT Tuesday: A prominent central CONUS ridge axis will
build from the southern plains to the Great Lakes on Friday,
wrapping over in Rex block fashion atop the lingering trough axis
along the southeast coastline. At lower levels, flow will become
more easterly on Friday around the surface high to the north,
producing greater cloudiness and shower chances in our region -
especially in eastern upslope mountain areas.

The ridge will become dominant north of the region through the
weekend, while Hurricane Maria spins well offshore - east of the
coastal waters of FL/GA/SC. Subsidence over the southeast along with
surface high pressure along the southern Appalachians will keep the
region dry.

The complicated interaction of Jose and Maria over the western
Atlantic will make for high levels of uncertainty for early next
week. However, both GFS and ECMWF solutions keep any circulations
east of the Carolinas through Monday. The forecast will remain dry
with slightly above normal temperatures through the period.

&&

.AVIATION /15Z TUESDAY THROUGH SATURDAY/...
At KCLT this morning: A few waves of 010-015 cumulus will be seen
near KCLT and KHKY thru about 16z until mixing lifts bases to
VFR level.

Otherwise: High pressure will remain in control of the pattern as
it`s center shifts slightly south, possibly setting up nearly atop
the region.  Therefore all sites remain dry with llv moisture
sufficient for widespread fair wx cu amidst light/vrb flow.
With that, guidance does favor a hint of sely/swly flow this
afternoon, which is included at KCLT and the Upstate sites,
however this should be short lived and generally less than 5kts.
Chances for convection will be a bit higher across the terrain
today as upper heights fall slightly, however kept any wx from
KAVL at this time.  Lastly, did introduce patchy fog at KAVL/KHKY
overnight only in the form of 5sm MVFR visb around 8-9z given than
confidence is low per recent mornings` guidance verification.

Outlook: Chances for diurnally favored showers and possibly a
thunderstorm will increase each day this week.  The best chances
look to be Thursday and Friday as flow veers easterly and marginal
moisture advection returns across the region.  That said, the best
chances for restrictions will be from early morning fog across
the northern NC piedmont/foothills, as well as in the mtn valleys.

Confidence Table...

            14-20Z        20-02Z        02-08Z        08-12Z
KCLT       High 100%     High 100%     High 100%     High 100%
KGSP       High 100%     High 100%     High 100%     High 100%
KAVL       High 100%     High 100%     High 100%     High  88%
KHKY       High  96%     High 100%     High 100%     High  87%
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...HG
NEAR TERM...CDG/Wimberley
SHORT TERM...HG
LONG TERM...HG
AVIATION...CDG/Wimberley


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