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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS62 KGSP 272343
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
643 PM EST Sat Feb 27 2021

.SYNOPSIS...
A front stalled south of our region will gradually lift
northward as a warm front through Sunday. A cold front will approach
the southern Appalachians from the northwest Sunday night and cross
the area on Monday. Dry high pressure moves from the Great Lakes to
the mid Atlantic coast Monday night into Tuesday before unsettled
weather returns from the west Tuesday night into Wednesday. A
stronger storm system could arrive by Friday.

&&

.NEAR TERM /THROUGH SUNDAY/...
-- Changed Discussion --
As of 640 PM: CAD continues to decay with scatting develop for all
but the NW Piedmont and portions of the Northern Foothills. These
areas will likely continue to see low clouds this evening while
other areas see mainly high clouds.

The subtropical ridge near the area will maintain WAA thru tonight,
which will amplify as sfc cyclogenesis occurs over the Midwest. This
is expected to lead to abundant cloud cover once again, likely
joined by fog in the NC Piedmont and possibly the eastern part of
the Upstate, where the shallow fragment of the wedge should remain.
Dense fog is not out of the question given the pattern and guidance
consensus. A small PoP exists overnight over much of the mountains
and northern NC Piedmont via the same mechanisms; upslope forcing
along the southern Escarpment and adjacent mtn ridges will further
enhance chances there. Lows will be 15 to 20 degrees above normal
with some locations seeing steady or even slightly rising temps.

The low stratus looks likely to erode late Sunday morning,
though moisture higher aloft is expected to maintain mostly cloudy
conditions across the board. With the wedge finally dissolving in
the morning, that should allow deeper mixing; midlevel winds will
be fairly strong in the gradient between the Midwest low and the
Atlantic ridge. This should result in a breezy/gusty afternoon,
with temps reaching well into the 70s in many locations, a few
degrees shy of records at our climate sites. RH will not be low
enough for this to pose any fire danger concerns.
-- End Changed Discussion --

&&

.SHORT TERM /SUNDAY NIGHT THROUGH TUESDAY/...
As of 205 pm Saturday: Frontal zone will be approaching the
forecast area at the start of the period, then will sag southeast
across the area throughout Monday. A rather vigorous precip band is
expected to accompany the front across the TN Valley into the
southern Appalachians, with likely-to-categorical pops forecast
across the NC mtns by daybreak Monday, with high pops overspreading
the remainder of the forecast area throughout the morning. Sort term
model guidance continues to reveal a strong signal toward weakening
of the precip region as it move across our area, as low level
convergence diminishes due to disruption of the flow pattern by the
high terrain, and as deeper forcing remains north of the forecast
area. In fact, by early afternoon, it appears likely that there
won`t be a whole lot left of the frontal band as it`s pushing east
of the area. All this being the case, any excessive rainfall
concerns Sun night/Monday should be confined to the areas closer to
the TN border, and even there the threat appears marginal at best.
Guidance continues to depict scant instability (i.e., sbCAPE < 100
J/kg) in the warm sector ahead of the front. However, the weakening
forcing profiles do not support much of a high shear/low CAPE severe
storm threat, nor do the shear profiles, which are rather inadequate
given the paltry buoyancy.

Otherwise, high temps will generally occur during the morning across
the mtns, with temps steady (valleys) or slowly falling (peaks/ridge
tops) throughout the day. As usual, downslope warming will offset
any late morning/afternoon CAA across the Piedmont/foothills,
allowing max temps to again warm to above normal...by about 5
degrees or so. The remainder of the short term will see a return to
normal...if not a slightly below normal temps and dry weather.

&&

.LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/...
As of 220 pm Saturday: A split flow regime will dominate the pattern
across much of the Conus, with an active southern stream likely
bringing two rounds of precipitation during the period. Fortunately,
there is more of a consensus among deterministic global model
guidance regarding these two events, particularly an event that is
expected to unfold in the Tue night/Wed time frame, when a compact,
but rather potent upper low is forecast to move across the TN and OH
Valleys into the Appalachians. The GFS continues to be weaker/more
suppressed with this feature, but much less so than in yesterday`s
runs, giving us the confidence to bump pops into the
likely/categorical range for much of the forecast area after
midnight Tue night, with pops quickly tapering off from the west Wed
morning.  Current indications are that sufficient cool air will be
left in place by retreating surface high to create a wintry precip
concern across the mtns and perhaps the I-40 corridor in the
foothills/Piedmont. However, the absence of any signal of a strong
cold air damming event/mech to lock in cold air suggests such an
event would likely be of the nuisance variety.

Guidance is also in better agreement regarding potential impacts of
a southern stream system later in the week, although differences
remain regarding the details. Nevertheless, the GFS and
ECMWF/Canadian camps identified yesterday are definitely trending
toward one another, with a slightly more potent/wetter system
depicted in the ECMWF/Canadian, and a much less potent/not nearly as
wet and more phased flow solution per the GFS. As such, pops are
warranted Friday through early Saturday, but these generally remain
only in the 30-40% range. Temps are forecast to remain around, if
not slightly below climo through the period, although a brief return
to above-normal conditions may return Thursday ahead of the late
week storm system.

&&

.AVIATION /00Z SUNDAY THROUGH THURSDAY/...
-- Changed Discussion --
At KCLT and elsewhere: Low clouds have scattered out for all but
KHKY. Expect VFR through much of the evening where it`s already in
place. However, KHKY will keep IFR cigs through the evening. IFR
cigs return overnight with generally MVFR vsby. Conditions then
deteriorate further with LIFR to potentially VLIFR cigs before
daybreak. Vsby follows similar trends. KAVL will most likely see IFR
cigs and MVFR vsby as conditions there remain a little more mixed.
Isolated showers also possible at KAVL. Strengthening low level
winds mean LLWS develops overnight at KAVL as well. Conditions only
slowly improve Sunday morning with vsby improving first but IFR cigs
lingering to nearly 18Z before lifting to low VFR or even scattering
out. Light and variable winds this evening and overnight become s to
SW during the morning. Winds increase and become gusty for the
afternoon. KAVL will see light S wind through the night with an
increase in speed for the afternoon.

Outlook: Flight restrictions and chances for precip are expected to
return Sunday night and linger into early next week. Drier high
pressure will build back into the area by Tuesday.

Confidence Table...

            23-05Z        05-11Z        11-17Z        17-18Z
KCLT       Med   78%     Med   60%     Low   45%     Med   72%
KGSP       High  94%     High  85%     High  85%     High  83%
KAVL       Med   66%     High  90%     High  80%     High  94%
KHKY       High  89%     Med   75%     High  90%     Med   78%
KGMU       High  94%     High  80%     High  80%     Med   78%
KAND       High  94%     High  90%     High  90%     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 are available at
the following link:

www.weather.gov/gsp/aviation
-- End Changed Discussion --

&&

.GSP WATCHES/WARNINGS/ADVISORIES...
GA...None.
NC...None.
SC...None.

&&

$$
SYNOPSIS...DEO
NEAR TERM...RWH/Wimberley
SHORT TERM...JDL
LONG TERM...JDL
AVIATION...RWH