Area Forecast Discussion
Issued by NWS Greer, SC

Home | Current Version | Previous Version | Graphics & Text | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
FXUS62 KGSP 211755

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
155 PM EDT Wed Mar 21 2018

A complex low pressure system will gradually move off the Atlantic
Coast today with colder air overspreading the region as the low
moves over the Atlantic. Drier high pressure will briefly return
over the area on Thursday, with another moist low arriving from the
west during the weekend.


As of 1045 AM...RADAR is showing good snowfall returns across the
NC/TENN Border region as bndy layer winds have picked up and are
starting to show some decent gusts, especially above 3500ft or so.
As of about 10am, most of the snow has ended outside of the higher
terrain as cloud cover has gradually filled across the SC Upstate.

Otherwise, latest sfc analysis continues to depict a slow-moving
meso-low centered over the FA this morning, which is aiding in the
supply of moisture, all which has been sparking the aforementioned
precipitation. Otherwise, the next Nor`easter is well on it`s way up
the eastern seaboard, with a secondary sfc low to the north across
WV, both of which are ushering colder air in around the backside
into northeast GA and the Carolinas. Continue to expect an upper
shortwave to push through the Southeast this morning through into
the afternoon hours, per latest guidance. This with colder
temperatures pushing into the northern foothills and along the I-40
corridor and moisture in place, anticipate that a rain/snow mix with
periods of light snow will break past the mountains and into these
areas, thus warranting the expansion of the Winter Weather Advisory
(on the previous shift). Though yesterday`s warm temperatures will
overall keep roads wet, significant travel hazards are not expected
at this time, but a dusting of snow is possible on grassy areas and
bridges and overpasses. Areas within the Winter Storm Warning,
especially along the higher elevations, should plan on difficult
travel conditions, along with scattered power outages and brief
reductions in visibility as gusty northwest winds are expected as
well. Further south towards the NC/SC border, potential for
rain/snow mix will decrease, with a changeover to all rain just
north of the Charlotte-Metro area and westward to east of the
escarpment, but would not entirely rule out a few snowflakes briefly
mixed in. Areas across the Upstate will remain overall dry, with the
exception of light showers possible this morning east of I-26.

With the exception of the western mountains, and Rabun county in
northeast Georgia where NW flow will keep snow showers through
tonight and into early Thursday morning, expect precipitation to
taper off by this afternoon as our moisture supply is cutoff, giving
way to a dry and cold day across the Upstate and NW Piedmont - not
an ideal start to Spring. Cold and dry will be the story for tonight
as well across the Upstate and NW Piedmont with overnight lows
dipping into the low 30s, just at or below freezing across the
Upstate and NW Piedmont and mid to upper 20s (upper teens in some
locations) across the mountains where light snow showers will
persist, tapering off from east to west towards the TN border
through morning.


As of 315 AM Wednesday: As the deep eastern cyclone moves farther
off the Atlantic coast, deep-layer northwesterly flow will continue
over our forecast area Thursday through Friday. Breezy to windy
conditions will linger through the period, especially over the
mountains, but with gusts below advisory criteria. Generally drier
high pressure will arrive from the west, however, a plume of mid-
level moisture may also arrive in the northwest flow Thursday night
into Friday. This moisture is not expected to be especially deep nor
be accompanied by any appreciable forcing, so PoPs will be minimal -
with just slight chances in the western mountains late Friday.


As of 335 AM Wednesday: Heights will fall over the plains on Friday
night, leading to a flattening of the upper flow pattern over the
southeast through Saturday. A warm front extending southeast of the
resulting plains/Midwest system will activate and provide upglide
from Illinois to the western Carolinas by daybreak Saturday.
Temperatures will be interestingly cool along the northern tier of
our forecast area with some mixed ptypes, mainly rain versus snow,
possible along and north of I-40 around onset. The deepest moisture
and forcing with this system may affect our area Saturday night
ahead of the low pressure center approaching from the west. The wave
should move east along the frontal zone draped through the region on
Sunday, and then offshore on Monday.

Temperatures will cool with this wave passage and strong surface
high pressure building to the north of the area will likely yield a
classical cold air damming configuration through Monday. However,
the numerical models are split over whether precipitation can return
over the wedge front into the cool air over our region. The GFS
brings the moisture back, while the ECMWF has strong but dry cold
air damming through Monday. Given the uncertainty, will blend
solutions and maintain low end PoPs for rain/snow - although a real
mixed bag of ptypes will be possible if precipitation develops
quickly over the wedge layer. The combination of wet systems and
then cold air damming will keep maximum temperatures some 10 to 15
degrees below climo through the period.


At CLT and elsewhere: A mix of low stratus and SCT to BKN mid-level
clouds will continue to stream across the forecast area this afternoon
and into this evening. All sites should see predominately VFR conditions
thru the 18z taf period with only KCLT carrying a brief TEMPO for -RA
from roughly 18 to 20z. The main concern will be the persistent gusty
NW winds that are expected to last well into the evening, and gradually
taper off later tonight (except for KAVL where they will likely continue
thru the entire taf period).

Outlook: VFR conditions expected through Friday, with increasing
precipitation chances this weekend.

Confidence Table...

            18-24Z        00-06Z        06-12Z        12-18Z
KCLT       High 100%     High 100%     High 100%     High 100%
KGSP       High 100%     High 100%     High 100%     High 100%
KAVL       High  99%     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:


NC...Winter Weather Advisory until 8 AM EDT Thursday for NCZ053-059-
     Winter Storm Warning until 8 AM EDT Thursday for NCZ033-


AVIATION...JPT is the U.S. government's official web portal to all federal, state and local government web resources and services.