Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 101953

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
253 PM EST Sat Dec 10 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 215 PM EST: The upper level flow pattern will become
increasingly zonal tonight into Sunday. Meanwhile, cold and dry
surface high pressure centered over the Appalachians will move off
the east coast through Sunday. With any appreciable mid level
moisture moving by to the north, overnight 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 south/southeast upslope areas
as well as across the lower piedmont late in the day. Onset profiles
are marginally cold/dry enough for a light rain/snow mix along the
higher ridges with any early arriving precip, but this will not be
featured since PoPs are so low. 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 through the
period as surface high pressure moves from the Appalachians to the
Atlantic coastal waters. High, thin clouds will increase through the
period, but low level Atlantic upglide moisture will begin to invade
from the southeast toward the end of the period. Will keep any late
Sunday morning cloud bases at VFR levels, but MVFR will be
increasingly possible just beyond the TAF period. Winds will be
light throughout and mainly southerly early in the period. Some
adjustment back toward easterly is expected across the foothills,
but southeasterly should be a good average through 18Z.

Outlook: Moisture will increase ahead of an approaching cold front
Sunday night through Monday with mainly a cold rain and associated
restrictions expected. Conditions remain unsettled through mid week
as the passing front stalls just to the south of the area and
moisture returns.

Confidence Table...

            20-02Z        02-08Z        08-14Z        14-18Z
KCLT       High 100%     High 100%     High 100%     High 100%
KGSP       High 100%     High 100%     High 100%     High 100%
KAVL       High 100%     High 100%     High 100%     High 100%
KHKY       High 100%     High 100%     High 100%     High 100%
KGMU       High 100%     High 100%     High 100%     High 100%
KAND       High 100%     High 100%     High 100%     High 100%

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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