National Weather Service National Headquarters

• Home
• Site Map
• News
• Organization
• Search for: NWS All NOAA 

-- Discussion containing changed information from previous version are highlighted. --
000
FXUS62 KGSP 280243
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
943 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 940 PM: The subtropical ridge near the area will maintain WAA
thru tonight, which will amplify as sfc cyclogenesis occurs over the
Midwest. This will lead to abundant cloud cover once again, with
areas of fog, some dense across much of the area outside of the
mountains tonight. Dense fog has been patchy and short lived, but
could become widespread and constant enough for a Dense Fog Advisory
overnight. 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 fog and low stratus will only slowly erode Sunday morning, with
fog dissipating by late morning but clouds lingering possibly into
early afternoon. After scattering, 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 /03Z 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...

            02-08Z        08-14Z        14-20Z        20-00Z
KCLT       High 100%     Low   49%     Med   71%     High  98%
KGSP       Med   72%     Med   65%     Med   75%     High  98%
KAVL       High  98%     High  83%     High  94%     High 100%
KHKY       Low   58%     Med   77%     Med   64%     High 100%
KGMU       High  80%     Med   66%     High  80%     High  98%
KAND       High  98%     Low   54%     Med   67%     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 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