Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 110606

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
106 AM EST Sun Dec 11 2016

Cold high pressure overhead tonight will move off the mid
Atlantic coast Sunday as another cold front crosses the Plains
states.  Expect this front to cross our region Monday with rain
chances remaining into mid week. Another blast of cold air will
settle across our area in the later half of the week.


As of 1250 AM EST, the upper level flow pattern will become
increasingly zonal through the period. Meanwhile, cold and dry
surface high pressure centered over the Appalachians will move off
the east coast. With any appreciable mid level moisture moving by to
the north, this morning`s clouds should be confined to thin cirrus
and another cold night of mins in the 20s throughout is expected.

Broad upper troughing will then develop through Sunday over the
central CONUS. Meanwhile, 850 mb flow will toggle southerly
overnight and increase through Sunday, with low level Atlantic
upglide moisture steadily making a run into the region from the
southeast. Anticipate mainly an increase in clouds, but with
isolated light rain PoPs developing in most areas from the Blue
Ridge east by late in the day. Actually, considering that the
profiles in most short term models become nearly saturated in the
lowest 5kft, but dry out quickly above about 0 C, this has the
appearance of more of a drizzle concern, and areas of drizzle
wording has been added to the forecast along with the small pops for
-RA. Onset profiles are marginally cold/dry enough for freezing
drizzle along the NC Blue Ridge, and will need to evaluate this
further in the coming hours. In addition, ridge top winds will
become gusty in the improving southerly flow through Sunday
afternoon. Temps will rebound marginally, but the rise will be
limited by increasing clouds despite the improving southerly flow.


At 2 PM Saturday: on Sunday night nearly zonal upper level flow will
be in place over the CONUS. This pattern persists into Tuesday, with
the bulk of upper level energy channeled across the northern tier of
states. The GFS does show and advection vort lobe crossing the
Southern Appalachians on Monday morning however.

At the surface, on Sunday night moisture will be increasing across
Northeast Georgia and the Western Carolinas in advance of an
approaching cold front. The front reaches the Southern Appalachians
by Monday morning, moving to the Piedmont by afternoon. The front
stalls to the south of our area on Monday night, while moisture
persists to its north across our area. This pattern persists into

Precipitation over our area is expected to start as early as late
Sunday in the mountains, and spreading east across the rest of the
area Sunday night. The main issue with this forecast will be
precipitation type on each night. With a warm nose aloft present,
snow is not expected. Some guidance suggests freezing rain in
isolated portions of the mountains, while other guidance is warmer
to begin with and would support liquid rain. Temperatures will
generally run above normal.


As of 245 PM EST Saturday:  The medium range fcst period kicks
off on Tuesday night amidst broad cyclonic flow aloft, while a
cold frontal axis slowly shifts south through north GA into the
Carolinas.  Behind this front is a rather broad cold/dry continental
high pressure system that should be promoting modest/improving
caa across western NC at fcst initialization.  As such, moist
northwest H85 flow looks to lift mechanically along the western
slopes of the southern Apps thereby yielding a brief round of nwfs
Wednesday morning, while further south thermal fields look to warm
to yield any wintry ptypes, thus all liquid is favored.

This all rain ptype will remain persistent into Wednesday evening
before Canadian high pressure dives through the Plains into
the OH/TN valleys ushering a reinforcing cold front across the
southern/central Apps Wednesday night into Thursday.  Developing
H85 northwesterly flow will once again promote upsloping during
this time frame, with latest accums across the NC high terrain at
generally 1-1.5 inches of less.  This cold ridge of high pressure
will slide east through the remainder of the week, setting up as
classical or hybrid CAD event (Depending on which model source is
favored).  Nevertheless, both the ECMWF/GFS favor some degree of a
developing Miller B pattern as a Plains low ejects northeast into
the OH valley, spreading moisture northward atop the entrenched
CAD Friday night, while an Atl coastal low develops by Saturday
afternoon/evening.  Profiles during this Miller B setup will
initially favor wintry precip Friday evening/night into Saturday
morning before warm advection yields a ptype phase change to all
liquid by midday Saturday.  It should be noted that confidence in
ptypes is rather low at this range therefore only a rain/snow mix
was featured in the fcst, however profiles do suggest that fzra/ip
could also be in the mix.  Temperatures through the period will
start out near/above normal, falling below normal into Thursday and
thru Friday behind the reinforcing front, before finally warming
back to near normal amidst the late fcst period warm advection.


At KCLT and elsewhere: VFR conditions will continue over about the
next 12 hours. By early Sunday afternoon, a very moist low level air
mass will push into the area from the south, and this is expected to
result in MVFR to low VFR cigs rapidly overspreading the forecast
area. Additionally, raw model output is producing precip across much
of the area from Sunday afternoon into the evening. However, based
upon vertical profiles, it appears to be more of a drizzle scenario,
and -DZ has been added to the terminal forecasts, as cigs fall
through MVFR to the 010-020 range by the end of the period. Would
not at all rule out IFR cigs developing Sunday evening, but this is
far too uncertain to add to the forecast attm. Visby may also begin
to deteriorate during the evening, although this will depend largely
upon the intensity of any DZ. Winds will remain light, but generally
favor a light SE direction this morning, possibly becoming light NE
during the afternoon and evening.

Outlook: Restrictions and light precip will remain possible late
Sunday night into Monday as a weakening cold front crosses the area.
Conditions could remain unsettled through much of the week as the
front stalls just to the south of the area and moisture returns.

Confidence Table...

            06-12Z        12-18Z        18-24Z        00-06Z
KCLT       High 100%     High 100%     High  80%     High  85%
KGSP       High 100%     High 100%     High  86%     High 100%
KAVL       High 100%     High 100%     High  86%     High  96%
KHKY       High 100%     High 100%     High  86%     High  89%
KGMU       High 100%     High 100%     High  87%     High 100%
KAND       High 100%     High  80%     High  94%     High  97%

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:




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