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FXUS62 KGSP 252307

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
607 PM EST Sat Feb 25 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.


2315 UTC Update: Sky cover was updated per visible satellite 
imagery, a with a decrease resulting across most of the area.

As of 200 PM: Low pressure now over Ontario/Quebec continues to
drive a cold front across the Eastern Seaboard. Winds have shifted
to NW across the mountains and foothills, and begun such a shift
over the upper Piedmont. A few gusts upwards of 35 mph have occurred
in isolated locations near the wind shift line. Expect frequent
gusts of 20-25 kt in all areas until late afternoon. Convective
coverage ahead of the front has peaked within our CWFA, and while
a few congested cu remain in the I-77 corridor, it appears safe to
remove all PoP from the near term forecast. There no longer appears
to be enough moisture to expect upslope showers in the mountains.

Once the wind gusts diminish, 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: A cold front will depart to the east, 
followed by cool, dry air through Sunday. No cig or vsby restrictions 
are expected. The main issue will be gusty NW winds, which will 
gradually decrease overnight. Light winds will back to the SW on 
Sunday afternoon.

Outlook: A shortwave exits the lower Mississippi Valley on Monday, 
once again increasing chances for precipitation/restrictions which 
may last into Tuesday. Somewhat unsettled weather will last until 
the passage of a cold front associated with another Midwest low late 

Confidence Table...

            23-05Z        05-11Z        11-17Z        17-18Z 
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:


The 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.




NEAR TERM...JAT/Wimberley

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