Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 242122
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
522 PM EDT Sat Sep 24 2016

.SYNOPSIS...
A broad upper ridge and surface high pressure will remain in place
over the southeast through tonight, then break down Sunday as an
upper trough approaches from the Mississippi Valley. A slightly
cooler and moist airmass will begin Sunday as a frontal boundary
settles into the area from the north. Unsettled weather is likely to
linger through the first half of next week before drier and cooler
air enters behind the passing cold front by the middle of next week.

&&

.NEAR TERM /THROUGH SUNDAY/...
As of 510 PM: KGSP radar indicated a few showers across the western
NC mtn counties. I will update the forecast to increase PoPs to schc
under the showers through 23z. Otherwise, I will keep temps nearly
steady over the next hour, then diurnal cooling through the evening.
KAVL tied todays high temperature of 89 set in 1895.

Previous discussion...
Areas of few-sct cu and maybe a small sw nc ridgetop shower will
dissipate with loss of htg early this evening.  Still expecting a
back door cold front to approach from the north tonight with an
accompanying wind shift back to NE and an associated stratocu field
across western NC during the late night hours.  The southward push
of said boundary is expected to slow on Sunday, as it becomes
parallel to the upper flow. This may serve as a focus for scattered
deeper convection during the afternoon along with scattered activity
in the favored terrain-aided locales.  With the push of lower
thickness values into the northern cwfa, and the potential for
cloudy skies to start off the day on Sunday, maximum temperatures
are slated to be 10-12 deg f cooler than today along I-40, but will
be close to persistence on the warm side of the front, acrs the far
sw cwfa.

&&

.SHORT TERM /SUNDAY NIGHT THROUGH TUESDAY/...
As of 235 PM EDT Saturday: Back door cold front remains stalled
across the area Sunday night with high pressure weakly ridged into
the area from the NE. With a moist low level southerly flow in
place, expect scattered showers to remain over the area through the
night. Any storms should be pushed southeast toward the frontal
boundary. Lows will be around 10 degrees above normal.

The front will wash out on Monday as a cold front moves to the spine
of the Appalachians and into the area Monday night. The moist low
level southerly flow continues through both periods. Expect at least
good coverage of showers across the area with scattered
thunderstorms as moderate instability develops. Even with the front,
shear remains light, so severe chances are minimal. However, there
should be some beneficial rainfall with the convection as QPF
forecasts are up to half an inch across the mountains and foothills.
Highs Monday will be cooler "only" up to 5 degrees above normal.
Lows Monday night will be 5 to 10 degrees above normal.

The guidance shows a little timing difference on the speed of the
cold front moving through the area on Tuesday. Best chance of
precipitation will be outside of the mountains with any solution.
That said, scattered convection is expected during the morning even
where chances are lower. Instability should remain weak, but high
enough for scattered thunderstorms, especially outside of the
mountains. Highs will be near normal mountains and a couple of
degrees above elsewhere.

&&

.LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/...
As of 150 PM EDT Saturday: We begin the medium range/extended with a
change in airmass Tuesday night as the cold front moves east and
away from the Interstate 85 corridor toward the coast. The forecast
deep closed upper low will be centered over the Great Lakes Tuesday
night.  The ECMWF has this low centered over the western Carolinas
Thursday night. The GFS on the other hand has this low opening up
with the westerly flow Wednesday night and moving the trough east
and off the east coast by Thursday night. We will be keeping the
medium range forecast dry after the few departing showers early
Wednesday. At this time do not believe the closed low will wobble
this far south along there is a possibility that the closed low will
become detached from the westerlies and wobble around for a few
days.

Temperatures will be near normal Wednesday then about a category
below normal Thursday through Saturday.

&&

.AVIATION /21Z SATURDAY THROUGH THURSDAY/...
At KCLT, just a few cu and light ne winds until about sunset leading
to a clear and nearly calm evening.  Toward Sunday morning within
developing NE flow, there is the possibility of stratocu development,
possibly dipping into the mvfr range before scattering out midday.

Elsewhere, light winds with few-sct cu dissipating this evening.
Overnight, the best chance for dense valley fog developing will be
across the southern/sw NC mtn valleys although cig restrictions may
develop by daybreak north of I-40. MVFR/IFR cigs have the potential
to be seen at least briefly all across western NC through about
mid-morning Sunday.

Outlook: A back door cold front will push into the region on Sunday,
bringing increased moisture for early next week. Another cold front
will push in from the west on Tuesday, bringing the best chance for
showers and possibly some TSTMS. Then dry high pressure returns
midweek.

Confidence Table...

            21-03z        03-09Z        09-15Z        15-18Z
KCLT       High 100%     High 100%     High 100%     High  87%
KGSP       High 100%     High 100%     High 100%     High 100%
KAVL       High 100%     High 100%     High  91%     High 100%
KHKY       High 100%     High 100%     High  98%     High  86%
KGMU       High 100%     High 100%     High 100%     High 100%
KAND       High 100%     High 100%     High  83%     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...DEO
NEAR TERM...NED
SHORT TERM...RWH
LONG TERM...DEO
AVIATION...CSH



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