Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 140606

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
106 AM EST Thu Dec 14 2017

A dry cold front will cross the area from northwest to southeast
today.  Thereafter, dry and cool high pressure will dominate our
weather through Sunday morning. Weak southerly flow with limited
moisture will return to the area Sunday and Monday as another cold
front approaches from the west.


As of 100 AM Thursday: No significant changes with this update.
Winds are howling above about 5000 ft, as expected, but valleys
remain sheltered with light winds. The southern fringe of a stratus
deck associated with the fast-moving clipper low is banking up
against the Northern Mountains, but otherwise, skies are clear. No
signs attm of any snow reaching the ground with those clouds. A Wind
Advisory remains in effect for portions of the NC mountains through
7 AM Thursday morning.

As another shortwave trough/weak clipper system propagates
southeastward through the Ohio Valley tonight, another dry cold
front will make it`s way towards the Carolinas. Behind the front,
northwest flow/CAA returns and with relatively shallow low-level
moisture. The clouds associated with this feature are approaching
the mountains as seen on sat pix. Cloud tops are around prime ice
nucleation temps of -15 C. Therefore, the combination of NW upslope
flow and CAA will lead to isolated light snow showers or flurries
across the usually favorable locations near the TN border. That
said, given the shallow nature of the moisture, weak CAA, and quick
movement of this system, so not expect any significant accumulation
with a dusting at best. Expect temperatures dip into the lower 30`s
overnight (mid to upper 20`s across the NC mountains), slightly
warmer than last night.

Expect another quiet day as the cold front slows down and nearly
stalls just south of the area across NC/SC. Despite the passage of
the cold front, downsloping will allow afternoon high temperatures
to climb into the low to mid 50`s across the Upstate and Piedmont,
though cooler into the 40`s across the Appalachians.


As of 100 PM EDT Wednesday:  The short term fcst period kicks off
on Thursday evening amidst zonal H5 flow, while at the surface a
dry cold front settles in from the west/northwest.  High pressure
behind the front will push east into Friday, setting up over the
Delmarva by daybreak.  With that, expecting dry/cool conditions
to return Friday amidst partly/mostly cloudy skies early on,
gradually sct`ing out into the day.  Meanwhile a northern stream
wave will work through the Great Lakes region, aiding erosion of the
aforementioned Delmarva ridge.  By daybreak Saturday the trof axis
associated with the northern wave will have passed allowing for a
gradual trend of rising heights aloft, and surface high pressure
development across the southeast states.  Therefore expecting dry,
sunny, and thus slightly warmer conditions on Saturday to round
out the period.


As of 145 PM EST Wednesday: the extended fcst picks up at 00z on
Sunday with the upper pattern flattening out as upper ridging
builds to our south. As we move into Monday, upper ridging persists
over the region as an embedded southern stream H5 trof digs down
across the southwest and moves eastward. The ECMWF continues to be
more progressive with this system and brings it to our doorstep by
late Monday/early Tues, 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 00z Wed, with the pattern amplifying again
later on Wed. At the sfc, the pattern will remain dynamic thru the
period with quite a bit of uncertainty remaining wrt the pattern
evolution. High pressure will be centered over the area at the
start of the period early Sunday, and slide off the coast later
in the day. Beyond this point, the pattern evolution remains fairly
uncertain 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 next cold front will approach the CWFA late Sunday
and move thru the area by late Monday/early Tuesday. The models
do agree that by the end of the period on Wed, drying high pressure
will be overspreading the region again.


At KCLT and Elsewhere: A fast-moving clipper system will track
across the central Appalachians early this morning, dragging a
fairly dry cold front across the area during the late morning
thru early aftn hours. Other than some low VFR to MVFR stratus
banked up against the west-facing slopes of hte NC mountains,
condtiions should be SKC or FEW250. Cannot rule out a previous low
VFR cloud deck at KAVL early this morning, but guidance has backed
off that. Winds are elevated out of the SW early this morning, but
gusts have subsided. At KAVL, N wind with a strong WLY wind just
2000 ft AGL will keep a threat for LLWS for a couple more hours,
then up-valley winds should pick up and flow veer to more NWLY
by daybreak. Outside the mountains, SW winds will veer to more
W or WNW by midday, but should remain light. Tonight, low-level
flow quickly backs to SWLY again, with guidance hinting at enough
moisture for some low VFR clouds developing across the NC foothills
and piedmont. So will keep FEW050 at KCLT tonight.

Outlook: Potential for short-lived restrictions on Sunday with
rain showers. Otherwise expect VFR as a series of dry cold fronts
move through the area.

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...Wind Advisory until 7 AM EST this morning for NCZ033-048>052-


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