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769
FXUS62 KGSP 241154
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
654 AM EST Fri Jan 24 2020

.SYNOPSIS...
Moist flow over a cool wedge of high pressure will make for a
chilly, rainy day today. A cold front will cross the area tonight
bringing in drier air. Seasonally cool and dry conditions will
persist over the weekend.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 645 AM: High pressure centered over northern Quebec is ridging
down the Eastern Seaboard this morning. Water vapor imagery shows
a deep cutoff low over the Ozarks, which is expected to slowly
wobble eastward into the lower Ohio Valley today. A broad plume
of moisture is being advected north out of the Gulf in advance of
this low. Sfc temps wet-bulbed down very close to freezing across
much of the foothills overnight, allowing precip to fall as a
cold rain in almost all areas. Aloft a strong warm nose suggested
freezing rain was likely where temps fell below freezing, but only
a few ridgetop obs actually dropped that low. A few automated obs
in lower elevations have occasionally reported UP which suggests
sleet pellets mixing in from time to time. The warm nose should
only strengthen the rest of the morning, and temps warm slightly. No
impacts from wintry precip are expected aside from those few ridges
which could see some slight ice accumulation.

850mb winds of 40-50 kt will continue with the southerly flow into
the occluding system, and this jet will gradually traverse the
mountains and Escarpment through early afternoon. A Wind Advisory
covers the impacts of gusts from this flow, which will not mix
down too remarkably well within the WAA. Significant enhancement
to rainfall rates however will occur which means isolated spots
along the south-facing Escarpment, and in the Balsams, are likely
to see more than 2 inches rain for a storm total. Minor flooding
is possible in these areas.

Along and south of the wedge boundary, sfc-based instability will
develop within the warm sector of the system. While the major
deterministic models show this instability staying south and east
of our CWA, the 00z HREF ensemble max SBCAPE rises above 100 J/kg
in the eastern SC and southern NC Piedmont zones, so it is looking
like a close call. The strong midlevel flow results in 0-3 km shear
values up to 50 kt immediately ahead of the cold front as it moves
into those areas around or soon after sunset. Coupled with a low
LCL forecast, when SPC issued the new Day 1 Outlook they saw fit
to place a sliver of our far southeast CWA into the Marginal Risk
area for the associated tornado risk.

NW-flow snowfall is expected to develop late tonight in the wake of
the cold front, along the Tenn border. No significant accumulation
is forecast with unfavorably warm temp profiles in the layer of
lift, and winds taking their time to become orthogonal. East of
the mountains, the drier incoming airmass will bring PoPs to near
zero after midnight, though some of the hi-res WRFs depict stratus
and fog developing as the cold air moves over saturated ground,
beneath a subsidence inversion. Some cloud cover thus is fcst to
stick around thru daybreak in parts of the Piedmont.

&&

.SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/...
As of 130 AM Friday: Deep layered forcing continues to weaken early
during the short range. The mean sfc-h5 flow becomes w/ly to nw/ly
across the FA with meager amts of moisture affecting the wrn upslope
regions of the NC mtns. Dropped soundings across the spine indicate
a stg warm nose and very shallow llvl moisture...yet the entire
sounding will be below freezing...so no p/type concerns outside of
snow possibly transitioning to rain across the nrn NC mtns late
while available llvl moisture decreases. The llvl flow across the
central NC mtns including the Smokies will generally be w/ly which
will limit topo lift and subsequent snowfall amts thru early Sun.
For now...have generally a half inch or less and mainly confined to
the border region. The winds will be defined nw/ly across the
nrn NC mtns so even with lowering moisture...expect around an inch
of snow mainly the higher elevations like Beech Mtn. Overall the
event looks to remain sub-advisory yet slick roads will be possible
both Sat/Sun mornings.

A reinforcing cP airmass continues to mix in Sat/Sun which will keep
max and min temps right arnd normal. By Sun night...a srn stream low
will advance toward the FA area. The models have sped this system up
and there/s decent agreement with light precip reaching the wrn
zones after 00z. The srn mtns look to saturate up to h5 while sfc
temps drop below freezing. So...have introduced accum snow aft 03z
thru the period with up to an inch anticipated across the srn/cent
mtns and less so up the spine thru daybreak.

&&

.LONG TERM /MONDAY THROUGH THURSDAY/...
As of 235 AM Friday: Continued snowfall across the NC mtns will
yield little additional accum before the sfc layer rises abv
freezing by late morning. Expect arnd a half inch or so generally
abv 3.5 Kft. The models develop a more robust cP high building into
the region Mon afternoon...so expect dry conds earlier in the
period. Made some sigfnt changes to PoPs over the mid-week period.
The latest guidance has come in much drier wrt the evolution of a
srn stream system. The GFS and the ECMWF have suppressed a moist sfc
low further south than the previous runs while the 00z CMC is a
curious outlier...which continues to bring the low across the nrn
GOM with a good deal of moisture and diurnal snow over the NC mtns
Wed and Thu. Thus with some uncertainty...have left slight chance
PoPs in with non/accumulating -snsh across the higher terrain. Max
temps will likely rise a bit abv normal each day as good insol and a
w/ly downslope component offsets a reinforcing polar airmass.

&&

.AVIATION /12Z FRIDAY THROUGH TUESDAY/...
At KCLT and elsewhere: Warm advective flow over entrenched in-situ
CAD will mean LIFR will be the norm today, possibly lifting
to IFR later today. The heaviest precip is expected in the late
morning. LLWS criteria may be met at times across the Piedmont from
late morning to late afternoon, which has prompted a mention at
KCLT. A rumble of thunder is possible in the same timeframe across
the area, but chance of TS is too small to include. Furthermore
a very small chance of a storm producing damaging winds exists
around sunset. Cold fropa will bring precip to an end from west
to east this aftn and evening. A strong inversion is depicted as
lingering into Saturday morning above the PBL, which will allow
cigs to persist until close to daybreak. Cold advection over wet
ground may also generate fog.

Outlook: Dry conditions will persist Saturday through early
next week.

Confidence Table...

            12-18Z        18-24Z        00-06Z        06-12Z
KCLT       High  87%     High  84%     Med   64%     Med   69%
KGSP       High  83%     Med   78%     Med   65%     High  87%
KAVL       Med   75%     Med   69%     High  85%     High  87%
KHKY       Med   77%     High  83%     Med   64%     Med   60%
KGMU       High  81%     Med   73%     High  81%     High  94%
KAND       High  84%     Med   66%     High  87%     High  94%

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:

www.weather.gov/gsp/aviation

&&

.GSP WATCHES/WARNINGS/ADVISORIES...
GA...None.
NC...Wind Advisory above 3500 feet until 4 PM EST this afternoon
     for NCZ033-048>052-058-059.
SC...None.

&&

$$
SYNOPSIS...08
NEAR TERM...08
SHORT TERM...SBK
LONG TERM...SBK
AVIATION...08