Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 291852

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
252 PM EDT Wed Mar 29 2017

Dry high pressure will build into the area from the north through
tonight. Moisture will gradually increase through the day tomorrow,
with abundant moisture in place by Friday as a strong low pressure
system moves east from the Mississippi River Valley. Drier weather
will return for the weekend, with unsettled weather returning
early next week.


As of 250 PM EDT: Enjoy the rest of the afternoon and evening
because change is on the way. The upper ridge axis over the area
tonight slides east to the coast Thursday. High pressure remains
ridged into the area from the NE tonight into Thursday. Low level
moisture increases over the area tonight with deep layer moisture
increasing on Thursday as upper heights begin to fall and flow
becomes SW ahead of an upper low moving into the Mid-South. The low
level flow becomes steadily more upslope in nature tonight and
increases in magnitude Thursday. Isentropic lift increases through
time as well. All this leads to increasing clouds tonight and a
chance of rain and drizzle developing along the Blue Ridge after
midnight. This precip spreads out across the CWFA through the day
Thursday as deep moisture moves in and stronger forcing develops.

With the surface ridge nosed in from the NE and clouds and precip
developing, a cold air damming wedge develops. The guidance differs
a little on where the southern extent of the wedge and resultant
TMB. The NAM, ECMWF, and SREF all showing instability developing
over NE GA, much of the Upstate, and the NC Mountains indicating a
farther north boundary than the GFS. The GFS shows little to no
instability keeping the boundary farther south. Have gone with a
blend to come up with thunder chances Thursday afternoon. This keeps
TSRA limited to west of the French Broad valley in NC, and generally
west of I-26 across the Upstate and into NE GA, though only small
chances at best for northern Greenville and Spartanburg Counties.

Lows tonight will be quite mild 10 to 15 degrees above normal. Highs
Thursday will show the wedge pattern, with near normal readings
along and south of the I-85 corridor and the TN border counties.
Highs will be below normal along the Blue Ridge into the NC
Foothills and NW Piedmont.


As of 2pm EDT Wednesday: First of a series of strong dynamical
spring systems reaches the area Thursday night/Friday morning with a
round of showers and thunderstorms.  Current expectations are for
very marginal instability with CAPE below 500 j/kg and LI of -1,
combined with deep layer shear to 55 kts.  Showers and some thunder
are a good bet Thursday night/Friday morning, but severe potential
will depend on some improvement in parameters over what is now
forecast.  As the system moves eastward on Friday, diurnal warming
will increase instability, with improved chances for SVR as the
system exits out of eastern parts of the CWA.  Region should receive
useful amounts of rainfall with this first system Thursday night and
Friday morning with storm total rain amounts of around a half inch
to an inch, with locally heavier amounts with the deeper convective

Wedge/CAD regime in place on Thursday brings some low-level moisture
from the southeast into the area with some upslope showers in the
higher terrain.  Somewhat cooler air and CAD-related cloudiness will
limit the development of surface-based CAPE.  CAD will be disrupted
by wet passage of major frontal system Friday morning, with
low-level winds veering to westerly and eventually northwesterly
behind the front.  Frontal passage will be accompanied by gusty
winds, especially at higher elevations with 850mb winds of 30 to 40
kts. Passage of front will scour moisture and create drying
conditions for the balance of Friday and clearing by Saturday
morning; with fair weather on Saturday.

Temperatures on Friday will warm some over Thursday pre-frontal,
with post-frontal temperatures recovering rapidly on Saturday in
clear skies.


As of 215 PM EDT Wednesday: the extended fcst picks up at 00z on
Sunday with upper ridging building back over the region as a very
deep upper trof digs down over the SW CONUS. The upper trof will
approach the fcst area on Monday and move across the CWFA early
Tuesday. The system is expected to lift NE of the area by early
Wednesday with flat upper ridging spreading back over the region in
its wake. At the sfc, Canadian high pressure will be pushing into
the fcst area from the north early Sunday but is expected to drift
NE of the region later in the day. At the same time, a vigorous low
will develop over the ArkLaTex region and lift NE on Monday and move
a warm front over the Carolinas. The system is expected to lift
north of the fcst area on Tuesday and push a cold front thru the
CWFA as it does. Things should dry out late Tuesday/early Wednesday
as the low moves NE of the region. As for the sensible fcst, Sunday
should be dry with POPs ramping up quickly from SW to NE Monday
morning. Chances for widespread showers and thunderstorms, some of
which could be strong to severe, remain high Monday afternoon thru
early Tuesday with lingering showers possible for the remainder of
Tuesday. I kept a slight chance POP over the NW half of the CWFA on
Wed for any lingering showers. Temps will remain above normal, for
early April, thru the period.


At KCLT and elsewhere, surface high pressure will continue to build
down across the forecast area from the north today and persist
through tonight. Winds have toggled SE or ESE outside of the
mountains and SSE at KAVL. These winds will continue until this
evening when they toggle back to NE. They remain light SSE at KAVL.
Stronger ENE winds outside of the mountains and S wind at KAVL
expected Thursday morning. Low VFR clouds become BKN this evening
then lower to MVFR then IFR before daybreak as moisture increases
and upslope flow develops. Cigs lift back to low MVFR at KCLT but
remain IFR elsewhere with MVFR vsby developing as isentropic lift
and cold air damming wedge develops bringing rain and drizzle across
all but KCLT.

Outlook: Showers and thunderstorms develop over the SC sites and
possibly KAVL Thursday afternoon as the wedge weakens and
instability develops. The approach of a strong storm system will
bring continued chances of restrictions as well as a potential for
heavy rain showers and thunderstorms Thursday night and Friday.
Drier conditions will return again for the weekend.

Confidence Table...

            19-01Z        01-07Z        07-13Z        13-18Z
KCLT       High 100%     High  97%     Med   76%     High 100%
KGSP       High 100%     High 100%     Med   71%     High  96%
KAVL       High 100%     High 100%     Med   64%     High  95%
KHKY       High 100%     High  94%     Med   71%     High  84%
KGMU       High 100%     High 100%     Med   73%     High  93%
KAND       High 100%     High 100%     Med   71%     High  81%

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:




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