Area Forecast Discussion
Issued by NWS Greer, SC

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000
FXUS62 KGSP 231049
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
649 AM EDT Thu Mar 23 2017

.SYNOPSIS...
Cooler air lingers across the region through the end of the work
week. A warm and moist southerly flow develops this weekend as high
pressure moves off the coast and a cold front approaches from the
west. This will bring showers and thunderstorms into the area by
Sunday, which continue into early next week.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 645 AM EDT...Stubborn stratocu continues to develop over the
Upper Savannah Valley and western Upstate, affecting temps and
warranting an adjustment to the sky grids. But otherwise, the
forecast is on track.

As of 300 AM EDT...An upper ridge will build over the region today,
as a trough closes off into an upper low over the Colorado Rockies.
At the surface, high pressure will settle over the Mid-Atlantic
today, bringing the winds around from NE to SE. Forecast soundings
show a shallow layer of RH trapped under a strong subsidence
inversion around 5-7 kft. Southerly flow in that layer will keep
enough moisture and WAA to produce a stratocu deck, mainly across
the western third of the CWFA today. Otherwise, skies should be
mostly sunny. thicknesses support max temps about 5-8 degrees below
normal.

Tonight, as low-level high pressure drifts off the coast, southerly
flow will increase atop the CWFA, tapping into a little Atlantic
moisture. Both the NAM and GFS show some increase in stratus across
the Upper Savannah Valley, and possibly spreading up the Piedmont
overnight. So I will advertise an increase in clouds across the
western two-thirds of the CWFA by daybreak Friday. The depth of
moisture doesn`t look deep enough in the time-heights to support
precip. So will continue a dry forecast overnight. Min temps will be
at to slightly above normal.

&&

.SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/...
As of 215 AM EDT Thursday: An upper ridge axis moves into the area
Friday then slides to the coast Friday night. The center of surface
high pressure wedged into the area from the NE in cold air damming
pattern moves out into the Atlantic with the ridge taking on an
east-west orientation. This allows a moist southerly flow to begin
to develop creating isolated showers near the Blue Ridge along the
NC/SC/GA border. Highs Friday will be near to a little above normal.
Lows Friday night will be 5 to 10 degrees above normal.

An upper low moves into the mid MS valley Saturday and into the OH
valley Saturday night as a short wave rotates around the upper low
and into the TN valley. The surface ridge breaks down as a cold
front associated with the upper low moves toward the area. This
creates a stronger moist southerly low level flow. Deep moisture
moves in as well along with synoptic scale forcing. Precip chances
will slowly increase Saturday with best chance along the southern
Blue Ridge, but then quickly increases Saturday night with best
chances over the mountains and foothills. Highs will be 5 to 10
degrees above normal with lows 10 to 15 above normal.

&&

.LONG TERM /SUNDAY THROUGH WEDNESDAY/...
As of 345 AM EDT Thursday: Guidance remains in good agreement during
the medium range. The upper low moving east in the short range moves
into the Mid-Atlantic on Sunday swinging the associated short wave
across our area. Deep moisture and synoptic scale forcing move
through as well as a cold front approaches from the west. Precip
chances increase as a result then slide east Sunday night with the
short wave. There will certainly be enough instability and forcing
for thunderstorms to develop. Shear increases as well. This combined
with the forcing may be enough to produce isolated severe storms.

Precip chances continue Monday and Tuesday as another, albeit
weaker, upper low and associated short wave crosses the area. Again,
there will be enough instability for thunderstorms to develop.
However, with the weaker upper system, shear is much less with a
much lower severe storm chance.

Ridging builds in surface and aloft on Wednesday bringing an end to
precip chances. Temps 5 to 10 degrees above normal Sunday rise to 10
to 15 degrees above normal through the end of the period.

&&

.AVIATION /12Z THURSDAY THROUGH MONDAY/...
At KCLT and Elsewhere: VFR conditions expected through the period,
except for some MVFR cigs around the Upstate and NE GA early this
morning. The low clouds are expected to scatter out within an hour
or two of the 12z TAF issuance. However, a thin layer of moisture
trapped under an inversion around 6 to 7 kft will persist thru the
day and tonight over much of GA and into the western Upstate. The
associated cloud deck may expand north and east overnight tonight.
Some guidance, in particular the NAM, hints at MVFR stratus
developing again across portions of central GA and Midlands and
expanding toward the Upstate and KCLT sites right before daybreak
Friday. I will only mention that at KAND for now. Winds will favor
NE thru midday, then veer to SE this afternoon. Winds will back
somewhat again tonight, especially across the Upstate to ENE, but
should remain SE at KCLT thru the rest of the period. A few low-end
gusts will be possible at KAND, but otherwise, winds should stay 10
kts or less thru the period.

Outlook: Low level moisture begins to return from the south tonight
thru Friday, resulting in an increase in cigs. Some restrictions in
stratus may be possible Friday and Saturday mornings, especially
near the Blue Ridge escarpment. Precip chances return Saturday thru
Sunday.

Confidence Table...

            10-16Z        16-22Z        22-04Z        04-06Z
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 100%
KHKY       High 100%     High 100%     High 100%     High 100%
KGMU       High 100%     High 100%     High 100%     High 100%
KAND       High 100%     High 100%     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:

www.weather.gov/gsp/aviation

&&

.GSP WATCHES/WARNINGS/ADVISORIES...
GA...None.
NC...Freeze Warning until 9 AM EDT this morning for NCZ035>037-056-
     057-069-072-502-504-506.
SC...None.

&&

$$
SYNOPSIS...RWH
NEAR TERM...ARK
SHORT TERM...RWH
LONG TERM...RWH
AVIATION...ARK


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