Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 140817

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
317 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 245 AM Thursday: A clipper system will quickly track across
the northern Mid-Atlantic this morning, dragging a relatively dry
cold front across the CWFA. A stratus desk behind the front can be
seen on IR imagery slowly advancing SE toward the NC mountains.
Other than an isolated snow shower and/or a few flurries this
morning in the Northern Mountains, it looks dry today. Gusty winds
should begin to weaken as the clipper moves east. No changes needed
to the Wind Advisory, which expires at 7 AM. East of the mountains
should see plenty of sunshine and light winds. Temps will rebound to
near normal across the piedmont, but still below normal in the
mountains. Highs in the 30s to mid 40s in the mountains, and in the
50s east.

Tonight, weak sfc high pressure builds in under NWLY flow aloft.
Another clipper system will be entering the western Great Lakes.
Flow at 850 mb will back to SWLY ahead of this wave, with guidance
showing some RH and WAA across the NC foothills and piedmont. This
may produce a stratocu deck and affect min temps. Overall, there
will be some increase in clouds and temps near normal. Lows in the
20s to mid-30s.


As of 145 AM EDT Thursday:  It looks like a quiet end to the week,
weather-wise. A fairly strong short wave will pass on Friday,
but with no moisture to work with, this feature will hardly be
noticed but for cooling temps off about five degrees behind an
associated sfc boundary. The flow veers a bit more WNW Friday
night, but moisture looks even more meager than previous model
runs, and no longer supportive of including even a slight chance
of precip, so that has been pulled from the fcst. High pressure
should move across the region as a flat ridge builds in from the
west. Temps should rebound to slightly above normal for Saturday
as a result. Meanwhile, the next system will organize over TX and
lift northeast Saturday night. As it stands right now, it does not
appear that moisture or forcing will arrive before daybreak Sunday.


As of 245 AM EST Thursday: The medium range remains in a state
of flux and forecast confidence is fairly low, as is typical for
this time of year. The GFS and ECMWF are in reasonable agreement
at the start of the period with bringing a srn stream system
northeastward on Sunday, altho there are timing and strength
differences. Both agree that precip chances will develop from the
west, but perhaps not as quickly as previously thought. There is
consensus that a lead short wave will lift out and deamplify across
the TN Valley/Cumberland Plateau region. That would take the bulk
of the forcing and deeper moisture west of us, only brushing past
the NC mountains. The trend in the guidance is to hold off longer
and the fcst moves in that direction, but still has precip chances
reaching the mtns early enough in the day that temps will be cold
enough for a brief period of wintry mix over the Smokies. With
the trend seen in the model guidance, this is not expected to be
a problem, as more than likely the precip chances will get pushed
farther back while temps continue to warm because of strong warm
advection that takes hold during the day. The fcst is an attempt to
blend the two models with the old fcst from that point onward. Thus,
we ramp up to a chance of precip Sunday night more in line with the
ECMWF, and keep the chance through Monday and Monday evening. Model
solutions diverge after 00Z Tuesday, with the ECMWF being dry and
the GFS developing another wave that spreads precip across the
region Tuesday and Tuesday night. The fcst was nudged more toward
the drier ECMWF while favoring the chance of precip over the srn
fringe. We dry out Tuesday evening and stay dry Wednesday. Temps
will be above normal the whole time with fairly high thickness,
so any precip should be all liquid.


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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