Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 240031

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
831 PM EDT Thu Mar 23 2017

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.


As of 825 PM EDT:  Updated discussion for taf issuance.  Current
near term remains on track thus no sig changes were needed/made.

Previous Discussion:  With strong high pressure anchored to our NE,
dry conditions and mostly clear skies will prevail thru the
afternoon. As the center of the high slowly moves farther offshore,
sky cover is expected to gradually increase from the west this
evening. Simultaneously, southerly flow will increase across the
fcst area tapping into minor amounts of Atlantic moisture. Both the
NAM and GFS show some increase in stratus across the Upper Savannah
Valley, and possibly spreading up the Piedmont overnight. Thus, I
kept the increase in sky cover across the western half to two-thirds
of the CWFA by daybreak Friday. The moisture appears pretty shallow,
so I kept POPs below slight chance thru the morning. Overnight, low
temps are still expected to be right around normal with some
portions of the NC Piedmont and Foothills slightly below normal.


As of 245 PM EDT Thursday: The weekend looks like it will be a
transition to a more wet period, at least into early next week. The
upper ridge axis should be to our east and moving offshore Friday
night. This should push the surface high and surface ridge axis to
the south. Once this happens, moisture will return from the Atlantic
early Saturday and then from the Gulf later Saturday. Expect
we should see some forcing for light precip near the Blue Ridge
Escarpment of SC and northeast GA by daybreak on Saturday. From
there, precip chances gradually expand. Overall, the evolution
of the upper pattern favors continued moisture transport from the
Gulf. Initially, this will be the result of the ridge axis to our
east and an upper low moving from the Plains to the mid-MS valley
on Saturday. A nrn stream long wave ridge will have moved over
the top of the upper low while the old low gets kicked out by the
next low moving off the Rockies. This lifts the first upper low
northeast across the Midwest through Saturday night and Sunday. A
cold front being driven eastward by this feature will run out of
support to move it east and will probably stall just west of the
region on Sunday. Precip chances ramp up gradually through this
period into the categorical over the mtns and likely E of the Blue
Ridge, what with good forcing acting upon deep moisture. It is too
early to be concerned with severe weather with this system, but
we will have to keep an eye on developments off to the west. Temps
look to be above normal.


As of 225 PM EDT Thursday: The first half of the medium range will
be marked by a rather progressive pattern, before a return to a high
amplitude/less progressive pattern late in the period. Closely on
the heels of the late short term system, another short wave trough
will approach the area Monday into Monday night. Buoyancy will be
more than adequate for deep convection, and while shear will be
little more than adequate for organized convection, it is
interesting that guidance is trending toward more of a negative tilt
with the trough axis. The resultant strong forcing acting on a
modestly buoyancy air mass should yield at least an isolated severe
convective risk Monday afternoon and evening.

Conditions gradually dry out Tuesday, as the pattern gradually
amplifies, with an upper ridge expected to develop across much of
the eastern Conus by mid-week. The latter part of the medium
range should be generally dry, although we cannot rule out some
diurnal convection developing by Day 7, as some guidance members
progress the upper ridge to the East Coast and diurnal instability
returns with southerly flow. Otherwise, temps are expected to be
5-10 degrees above climo through the period.


At KCLT and Elsewhere:  Vfr through the vast majority of the taf
cycle with the exception of low stratus probs in the morning given
moisture advection from the south.  With that, guidance favors
persistent/increasing southerly moisture advection as the Western
Atlantic surface ridge continues to dominate.  Nam/GFS sounding
exhibit hints of low stratus around daybreak as llv moisture spills
into the region from the south.  Opted to carry mvfr cigs only at
the SC Sites and KAVL/KHKY, while featuring a tempo at KCLT for a
sct mvfr deck.  Otherwise, moisture will continue to increase over
the region through the day on Friday with low vfr clouds dominant
once any lower stratus erodes with mixing.  Winds are expect to
remain southerly and light on Friday.

Outlook: increased low level moisture returns from the south thru
Friday, resulting in increases in sky cover. Some cig restrictions
are possible Friday and Saturday mornings, especially near the Blue
Ridge escarpment and portions of the SC Upstate. Increased precip
chances return Saturday thru Sunday.

Confidence Table...

            00-06Z        06-12Z        12-18Z        18-00Z
KCLT       High 100%     High  93%     High  87%     High 100%
KGSP       High 100%     High  93%     Med   66%     High  88%
KAVL       High 100%     High 100%     Med   72%     Med   75%
KHKY       High 100%     High 100%     Med   76%     Med   76%
KGMU       High 100%     High  93%     Med   66%     High  89%
KAND       High 100%     High  93%     Med   71%     High  89%

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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