Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 260521

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
1221 AM EST Sun Feb 26 2017

Cooler high pressure will build into the region from the west
through Sunday. Warmer air should return during the first half of
next week. A warm front lifts north through the area around midweek
as a cold front approaches from the west bringing showers and storms.


As of 1220 AM EST Sunday:  Updated discussion for taf issuance.
Current fcst remains on track amidst building high pressure
therefore only minor tweaks to t/td and wind trends were made to
better align with recent obs.

Previous Discussion:  Clear and much cooler weather will return
to the area tonight as high pressure builds in from the west. Min
temps actually are expected to dip about a category below normal
in the Piedmont, and perhaps two in the mountains. This will be
followed by near-normal maxes Sunday.

The only impactful weather remaining in the period is the
elevated fire danger associated with low afternoon RH and
ever-drier fuels. This is particularly concerning today given
the brisk winds. We will maintain a Fire Danger Statement thru
600 PM. However, for Sunday, winds will be much lighter; we will
simply highlight low RH in the Fire Weather Forecast product,
and the evening or midnight shifts may re-evaluate.


As of 215 PM EST Saturday: General west/southwest flow aloft will
dominate the short term, with embedded shortwaves pushing through the
area. We begin the period with surface high pressure off the NC
coast, with southerly flow around the western periphery of that
surface high, slowly bringing another warm and moist airmass to the
region. Monday should see morning lows and afternoon highs fairly
close to seasonal averages, maybe a degree or two above, before the
low-level WAA really kicks in Monday night into Tuesday.

The first shortwave will bring increasing precipitation chances
during the day on Monday as isentropic upglide increases across the
Deep South and Southeast, and if the moisture arrives early enough,
there might possibly be enough cold air-moisture overlap for some
light snow in extreme western zones, but generally seems unlikely.
The low-level shortwave splits Monday afternoon, with the northern
wave damping. Precipitation falls apart over the Southern
Appalachians Monday night as moisture flow is temporarily cutoff by
an enhancement in precip along the SC coast with the southern
shortwave (this can also be seen in vorticity fields as the southern
vort stream intensifies as the northern one weakens Monday evening).
Another weak shortwave/vortmax gets lifted over the region Tuesday
morning ahead of a stronger upper level jet (to impact us at the
beginning of the extended). The upglide pattern looks messy with
lack of synoptic lift, but as usual generally favors the upslope
areas of the SW NC mountains. Overall not much to write home about
for QPF, but WAA increases Tuesday night ahead of the next system,
with overnight lows closer to seasonal highs.


As of 230 PM EST Saturday: During the short term, a longwave trough
will be pushing through the Rockies and into the Plains, to affect
our area at the start of the extended. Primary surface low over the
Great Lakes at the start of the period will connect to a secondary
surface low lifting from the OK/TX Panhandles toward the Mid-
Mississippi Valley at the start of the period, with the cold front
approaching the Appalachians Wednesday evening. Thankfully guidance
is in much better agreement today, with the GFS much slower and
lined up with the ECMWF and both depicting the frontal passage after
00z Thursday. This helps reduce severe potential as instability will
be limited, and what little may be leftover across the area
Wednesday night will be a little farther removed from the strong
deep-layer shear. Still, the best chance for thunderstorms across
the area will be with the frontal passage as mechanical lift adds
its oomph to the convective instability lingering from the
unseasonably warm temperatures on Wednesday (though frankly it`s the
seasonal temperatures that are starting to feel abnormal). Still
cannot completely rule out a strong to isolated severe storm (more
of a HSLC situation with <500J/kg sbCAPE with 50-70kt deep layer
shear, though the environment becomes decreasingly favorable after
00z Thursday).

Will see another battle of invading cold air across the mountains
pitted against retreating moisture, though with the help of some
weak moisture attendant with the upper trough axis behind the
surface front, and with this some light snow showers will be
possible early Thursday across the mountains before the moisture
completely dries up. Snowfall totals for now are less than an inch
but will continue to refine with later forecasts. The end of the
period will sport near-to-just-slightly-above average temperatures
as mean upper trough remains over the area. A shortwave rounding the
base of the trough may bring a clipper to the northern mountains
Thursday night; GFS is farther south with this feature than the
ECMWF. Have included very very light pops in the northern mountains
just to hint at this possibility, with cool Canadian high pressure
building into the area late in the week.


At KCLT and Elsewhere:  VFR through the period at all sites as
high pressure prevails at the surface beneath quasizonal flow
aloft leading to mostly SKC with a few high cirrus streaming aloft
late in the period.  Nwly winds will generally weaken through the
morning hours as the pressure gradient relaxes, with some mid/late
afternoon wswly backing possible at all sites.

Outlook: Dry conditions with very low chances for restrictions
expected to start the work week, before another upper impulse
approaches on Monday afternoon leading to increased chances for
precipitation/restrictions for Tuesday and again on Wednesday as
cold front approaches from the west late in the evening/overnight.

Confidence Table...

            05-11Z        11-17Z        17-23Z        23-00Z
KCLT       High 100%     High 100%     High 100%     High 100%
KGSP       High 100%     Med   72%     High 100%     High 100%
KAVL       High 100%     High 100%     High 100%     High 100%
KHKY       High 100%     Med   66%     High 100%     High 100%
KGMU       High 100%     Med   66%     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:


An area of high pressure will sit atop the region Sunday, and though
temperatures will be notably cooler (not breaking out of the 50s in
most areas), RH values will still dip to near 20 percent during the
afternoon. However winds are not expected to be much of a factor. A
fire danger statement still may be issued overnight in coordination
with other agencies.




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