210
FXUS62 KGSP 082005
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
305 PM EST Wed Jan 8 2025

.SYNOPSIS...
Cold and dry high pressure builds into the region through Thursday,
keeping temperatures well below normal. An area of low pressure will
form near the Texas coast early Thursday and track across the Gulf
Coast and reach the Carolinas Friday into early Saturday. Moisture
spreads over our region in the cold air with wintry weather
forecast which ends on Saturday as the low moves off to the east.
Dry and cold weather returns early next week.

&&

.NEAR TERM /THROUGH THURSDAY/...
As of 2:25 PM EST Wednesday: Temps remain below freezing across
the bulk of the NC mtns even as most of the lingering stratocu
has retreated to the NC/TN border. Nonetheless, there continues
to be plenty of stratocu upstream, banking up against the NC/TN
border. These clouds will likely surge a little further into the
NC mtns this evening, as the NW flow strengthens. The cloud tops
should remain cold enough for additional snow flurries to fall
along the NC/TN border this evening/tonight, however moisture
still appears too shallow for more substantial snow showers.

Otherwise, an h5 vort max will swing thru the Ohio Valley to the
Carolinas this evening, bringing a reinforcing shot of cold air
across the region. Winds will remain gusty tonight as they struggle
to decouple thanks to CAA/mixing, especially over the mtns where
gusts of 25 to 35 mph are likely across the higher elevations. We
still expect 850 mb temps to fall into the -12 to -15 C range along
the NC/TN border, suggesting temps will fall into the single digits
above roughly 3500 ft. These temps, combined with the gusty winds,
should produce apparent temps in the -5 to -12 F range overnight and
into Thursday morning over the northern mtns. As such, a Cold Weather
Advisory for Yancey, Mitchell, and Avery counties will be in effect
from midnight tonight until noon Thursday. Bkn clouds and sct snow
flurries will also likely continue well into the night near the NC/TN
border. Otherwise, mostly clear skies are expected with lows in the
teens to low 20s with apparent temps in the single digits to teens
early Thursday morning outside the mtns. This is close to Cold Wx
Advisory criteria, but not quite cold enough. Highs on Thursday will
remain roughly 10 to 15 degrees below climatology for most of the
area.

&&

.SHORT TERM /THURSDAY NIGHT THROUGH SATURDAY/...
Key Messages:

1) The Winter Storm Watch was expanded east, and now includes the
entire NC mountains, Foothills, and Piedmont, as well as the entire
SC Upstate.

2) Snowfall totals have increased since the previous forecast
issuance, while ice totals have remained similar.

As of 246 PM EST Wednesday: By early Friday morning, a potent
500mb trough will sharpen over the southern Great Plains, inciting
cyclogenesis over the Texas-Louisiana coastline, and driving the
resultant surface low northeast into Alabama.  This will usher
deep synoptic forcing into the Carolinas by late morning Friday,
intensifying as the low draws nearer.  The surface low will lift
into the SC Lowlands by day, with the warm front likely remaining
south of GSP`s forecast area for the duration of the event.  So,
a mature warm conveyor belt will lift out of Georgia late Friday
morning or early in the afternoon...and most operational guidance
depicts an abrupt onset to strong low-level WAA.  The strength
and altitude of this WAA will dictate how, exactly, onset proceeds.

Initially, most precipitation will fall as snow.  Temps will
have dropped well below freezing across the area Friday morning,
and the mid/upper levels will be saturated enough that nucleation
should not be an issue.  So, whatever falls will fall as snow...and
although a deep dry layer will be in place as precipitation begins,
guidance depicts such strong isentropic ascent that it won`t take
more than 1-2 hours for this layer to saturate...allowing for
things to pretty quickly evolve from dry conditions, to flurries,
to accumulating snow during the late morning or early afternoon.
Temperatures should max out before the normal diurnal max, peaking
at basically however warm it can get before precipitation begins and
temps begin wet-bulbing down.  This looks like it may take place as
early as the 9am-12pm window, at least for the western half of the
CWA, where things will ramp up sooner.  The details beyond this
point, however, are murkier.  During the evening and overnight,
WAA will continue, and some form of changeover from all-snow to
wintry mix appears likely.  The most recent 12z cycle of operational
guidance has sped up its handling of low-level isentropic ascent,
but in response to a more southward storm track, the resulting
warm nose is also higher - as high as 700mb per the latest NAM -
with a deeper subfreezing layer at the surface.  Accordingly,
calibrated sleet probabilities have increased at the expense of
lower snow and freezing rain probs...somewhat reducing overall
ice accumulations despite the robust warm nose.

Unfortunately, there`s still a lot of room for error, and a lot of
time for the forecast to change.  If low-level profiles get even a
tiny bit warmer, it`ll mean less sleet and more ice.  If the warm
nose gets stronger...less snow, more ice.  If the system speeds
up, QPF, which continues exhibit a lot of spread among ensembles,
could change, which would alter both snow and ice totals.  It looks
increasingly likely, though, that the Upstate won`t escape at least
a small amount of ice, and that zones as far north as I-40 will
be under the gun for some sleet.  Dreams of an all-snow forecast?
Quashed.

In any case, the synoptic pattern is progressive enough that dry
air should begin filtering in aloft and cutting off ice nucleation.
For zones to the south that are already experiencing freezing rain,
this won`t really matter, but for zones farther north, which may
still be experiencing snow, this will probably lead to a brief
changeover to sleet before precipitation ends altogether and skies
begin clearing.  Behind the system, a bitterly cold Arctic air
mass will settle into the region, such that highs Saturday will
barely hit 40 outside the mountains.

&&

.LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/...
As of 251 AM EST Wednesday: Upper ridging builds in behind the
departing low and ushers in cold, dry, continental high pressure
for the duration of the period.  A brief spurt of light NW flow
snow may be possible late in the period, but it generally looks
too dry.  Skies will be clear and temperatures will be a few
categories below normal for most of the period.

&&

.AVIATION /20Z WEDNESDAY THROUGH MONDAY/...
At KCLT and elsewhere: expect VFR conditions to prevail thru
the 18z taf period. We may see a few stratocu over the Upstate
and CLT later tonight/overnight, but otherwise skies should
remain mostly clear. Winds start out light and vrb and then
toggle to NWLY early this evening and remain NWLY for the rest
of the period. At KAVL, winds will remain steady and from the
NW thru the period with low-end gusts. Another round of lower-
level moisture will likely spread some sct to bkn clouds back
over KAVL this evening, but clouds should remain VFR level.

Outlook: Expect dry, VFR conditions to continue thru Thursday as
high pressure builds into the region. A low pressure system moves
in from the west Friday into Saturday potentially bringing wintry
precipitation and restrictions. Dry weather returns by early Sunday
and continues into early next week.

&&

.GSP WATCHES/WARNINGS/ADVISORIES...
GA...Winter Storm Watch from Friday morning through Saturday
     morning for GAZ010-017-018-026-028-029.
NC...Winter Storm Watch from Friday morning through Saturday
     morning for NCZ033-035>037-048>053-056>059-062>065-
     068>072-082-501>510.
     Cold Weather Advisory from midnight tonight to noon EST
     Thursday for NCZ033-049-050.
SC...Winter Storm Watch from Friday morning through Saturday
     morning for SCZ008>014-019-101>109.

&&

$$

SYNOPSIS...DEO
NEAR TERM...JPT
SHORT TERM...MPR
LONG TERM...MPR
AVIATION...JPT