Area Forecast Discussion
Issued by NWS Greer, SC

Home | Current Version | Previous Version | Text Only | 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 121942

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
242 PM EST Tue Dec 12 2017

Northwest flow moisture will dissipate over the mountains tonight,
with dry high pressure building over the region through mid-week. A
cold front will cross the area from the northwest Wednesday night
through Thursday before high pressure sets up through much of the
weekend. Low pressure and moisture are expected to return from the
west by early next week.


As of 230 PM Tuesday: A Winter Weather Advisory and Wind Advisory
remain in effect for portions of the NC mountains through 7 AM on
Wednesday. A Wind Chill Advisory will be in effect from 10 PM
tonight through 7 AM on Wednesday for portions of the NC mountains
as well.

Latest radar imagery continues to depict light snow showers falling
across portions of the NC mountains, mainly along the TN/NC border.
As total snow accumulations of 1 to 2" are expected in the higher
elevations, anticipate snow showers to taper off this evening with a
few flurries continuing into tonight.

Temperatures have warmed into the upper 40`s to lower 50`s this
afternoon but have likely peaked for today (upper 30`s across the NC
mountains). With a recently passed strong, dry cold front, currently
just east of the forecast area, northwest winds will continue to
increase across the area this afternoon as strong CAA builds in.
Though gusts will subside across the Upstate and Piedmont tonight,
expect increased winds to persist across the NC mountains overnight
into Wednesday morning. These increased winds along with
temperatures dropping into the lower teens to single digits across
the NC mountains will allow for wind chills to drop to around 5
degrees above zero to minus 10 degrees below zero in locations,
mainly above 3500 ft near the TN border. Elsewhere, overnight low
temperatures will drop into the low to mid 20`s, with wind chills in
the mid to upper teens.

As sfc high pressure becomes situated to our south and clouds
decrease during the morning hours, expect a quiet yet cold day
on Wednesday ahead of the next approaching system. With
northwest winds around 10 mph (slightly higher across the NC
mountains), afternoon high temperatures will climb into the low
to upper 40`s across the Upstate and Piedmont, where colder
temperatures in the 30`s will persist across the mountains.


As of 230 PM EDT Tuesday:  The short term fcst kicks off on
Wednesday evening as a Clipper wave slides across the southern Great
Lakes pulling a dry reinforcing cold front southward into the OH/TN
valleys by daybreak Thursday.  Guidance has trended slightly wetter
with this fropa, mainly focusing any moisture along western slopes
of the Appalachians where H85 flow remains veered nwly.  With that,
will continue the current low end pops across the central/northern
TN line mtn zones, with thermal profiles supportive of a few light
snow showers amidst gusty winds.  H85 flow looks to weaken into the
evening hours therefore any residual upslope snow showers should
wrap up quickly leading to a dry forecast to round out the period
as the front sweeps through the rest of the fcst area.

Meanwhile, another northern stream upper wave will dive through the
Rockies with deep layer flow across northeast GA and the western
Carolinas backing wly then swly overnight into Friday morning.
However, dry high pressure sliding east across the central
Appalachians will setup over/near the Delmarva by midday Friday
yielding weak cold advective nely flow in lee of the mountains.
Despite the intrusion of the weak front, temperatures across
the region on Thursday will be slightly warmer than recent days,
especially for the foothills/piedmont given ample downsloping and
thus modest insolation, not to mention possible backed swly sfc
flow thanks to lee troffing.  Temperatures will be cooler on Friday
as the aforementioned northern high edges southward into the region.


As of 220 PM EST Tuesday: the extended fcst picks up at 00z on
Saturday with the upper trof axis moving over the fcst area and
then rapidly lifting NE of the region over the next 12 to 24 hrs.
As we move into Sunday, the pattern flattens out as upper ridging
builds over the Greater Antilles. As we move into Monday, upper
ridging persists over the southeast as an embedded southern stream
H5 trof digs down across the Southern Rockies and moves eastward.
The ECMWF continues to be more progressive with this system and
brings it to our doorstep by Monday afternoon, while the other
long-range models are about 18 to 24 hrs slower. Either way, the
trof axis should be passing over the fcst area by the end of the
period on Tues. At the sfc, the pattern will remain dynamic thru
the period with quite a bit of uncertainty remaining wrt the pattern
evolution. On Sat, drying high pressure will slide in behind a departing
coastal low. The high is not expected to hang around for too long,
as it will shift NE and move off the Atlantic Coast on Sunday.
Beyond this point, the synoptic pattern becomes unclear as each
model has a different scenario wrt exactly where and when the
next sfc low will spin up to our west. They generally agree that
the later part of Sunday thru early Monday could be fairly wet
with some drying after that, however overall fcst confidence for
days 6 and 7 remains low at this time.


At KCLT and Elsewhere: Expect VFR through the valid TAF period as
latest satellite imagery depicts SCT/BKN high clouds moving overhead
across much of the forecast area, along with intermittent areas of
FEW/SCT/BKN MVFR stratus. Winds have shifted to the northwest behind
a recently passed cold front and are expected to persist out of the
northwest through the forecast period. Expect winds to increase to
10 to 15 kts with gusts up to 25 kts through this evening, and
higher to 30 kts possible at KAVL continuing through Wednesday
morning. A brief period of snow could reach KAVL over the next few
hours, but overall anticipate the majority of snowfall to stay
pinned to the TN/NC border, not affecting any other terminals.  On
Wednesday, VFR continues with passing high clouds and northwest
winds around 10 kts.

Outlook: Potential for flight restrictions  Thursday night into
Friday, especially at KAVL, with a system approaching from the west.
Otherwise expect VFR.

Confidence Table...

            15-21Z        21-03Z        03-09Z        09-12Z
KCLT       High  81%     High  82%     Med   68%     Low   56%
KGSP       Med   70%     Med   75%     High  83%     Med   64%
KAVL       High  94%     High  85%     Med   70%     High  87%
KHKY       High 100%     High  83%     Med   66%     High 100%
KGMU       Med   76%     High  86%     High  85%     Med   63%
KAND       Med   76%     Med   65%     High  90%     Med   61%

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 7 AM EST Wednesday for NCZ033-
     Wind Advisory until 7 AM EST Wednesday for NCZ033-048>052-058-
     Wind Chill Advisory from 10 PM this evening to 7 AM EST
     Wednesday for NCZ033-048>052-059.


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