Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 160824

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
324 AM EST Mon Jan 16 2017

A slightly cooler airmass today will give way to temperatures
well above average again by mid-week as a cold front approaches from
the west with light rainfall. Behind the front, temperatures will
cool slightly but remain well above normal. A warm front will move
through the Southeast Thursday and Friday, bringing another round of
showers. A more significant storm system will move into the
Southeast next weekend, increasing chances for widespread rainfall.


Back door cold front, best represented in surface data by a slight
dewpoint discontinuity, roughly bisects the forecast area early this
morning. Increasing moist isentropic lift in the vicinity of this
boundary will allow stratus to persist across much of the forecast
area through at least the morning hours, with ceilings likely
gradually lowering through this time. Light precip that earlier
developed over western NC has pretty much dissipated, but will
maintain a 20 pop in those areas through the morning.

By late morning/afternoon, there is a growing consensus among high
res model guidance that an area of showers associated with a migrant
low level theta-e axis, with perhaps a bit of weak associated
buoyancy, will push into the forecast area from central GA. It
should be noted that according to the HRRR, which is the most
aggressive with this scenario, this area of showers should already
be developing across southern GA, and there`s absolutely no sign of
it thus far. Nevertheless, based upon the signals in guidance, and
the expectation of persistent upglide and weak convergence in the
vicinity of the boundary, today`s highest pops (30 percent) will be
featured along and south of I-85 in the Upstate and GA, while slight
chances will be advertised elsewhere. Today`s temps will be
problematic due to uncertainty as to where the boundary will stall,
although the low cloud cover should at least hinder substantive
warming in most areas. The max temp forecast ranges from the upper
60s across the upper Savannah River Valley and the low valleys near
the TN border, to the lower 50s across the NE corner of the forecast

Precip chances will become more focused near the high terrain late
tonight, esp across the southern escarpment of the Blue Ridge, where
mechanical lift will increase as a consequence of accelerating
southerly flow in the H9-H8 layer responding to height falls to our W
and NW. Even so, pops will be 40 percent at best in these areas. Min
temps will remain well above climo.


As of 250 AM Monday: A strong subtrop high remains centered over the
Yukatan Penninsula and dominates the wx pattern across the SE CONUS
over most of the short term. Atl sfc high will ridge
across SC/GA and help slow down the advancement of a developing
moist cold front toward the CWFA. An h85 jet ahead of the front will
remain generally west of the area Tue relagating low-end topo lift and
sct -shra across the wrn zones thru the evening. The cold front will
eventually reach the mtns early morning Wed and become
quasi-staionary aligned within the northern periphery of the subtrop
high. This will warrant high end pops for -shra across most of the
mtns before a strong h5 s/w pushes the whole frontal system
southeast the CWFA by Wed afternoon.

The models are showing the potential for a few tstms across the SW
NC mtns early Wed associated with the strong s/w. There could also
be some thunder over the ern Piedmont by the afternoon as the s/w
and llvl convg zone interacts with a briefly destabilizing atmos in
strong bulk shear. Layered sky cover will remain high both
Tue/Wed...but with persistent sw flow...max temps will reach arnd 15
degrees above normal if not a few degrees higher. With all the cloud
cover and BL mixing...mins will only drop into the mid to upper 50s
non/mtns Tues night...and about 10 dgrees cooler Wed night behind
the front yet still about 15 degrees above normal for mid Jan.


As of 230 AM EST Monday: The medium range period is marked by
generally amplified flow over N. America, with a very active wave
train setting up over much of the CONUS, especially including the
southeast and mountain west. The period begins at 12Z Tuesday
morning with surface cyclogenesis occurring over northern Mexico,
and an upper level low ejecting towards the southeast from the
desert southwest. An old remnant surface high will be breaking down
over the southeast as a surface low approaches the region, and
though the high will be weak and in an unfavorable position for true
CAD to occur, a brief wedge of high pressure developing over our
area is possible late Thursday and into Friday, providing a focus
for isentropic upglide in an airmass that will already be moistened
considerably by a warm front passage and Gulf moisture return. At
the surface, late Thursday and Friday will likely feature widespread
rainfall across the region, especially considering the impressive
upper vort max associated with the the upper level low riding up the
spine of the Appalachians.

Some post-frontal passage clearing is likely Saturday before a
large, deep upper low cuts off and intensifies over the Central
Plains. Despite some brief upper ridging over the eastern CONUS, the
pattern remains progressive, and surface cyclogenesis occurs as the
low ejects out of the plains and crosses the OH river Valley. Though
guidance is in good agreement as far as timing of the warm front
passage/precip arrival in our area Saturday night and into Sunday
morning, QPF Sunday and into Monday morning remains unclear. PWs are
near record highs in some deterministic guidance, and high QPF
appears possible based on substantial upper forcing for ascent. On
the other hand, there are some signals for Gulf coast convection
possibly robbing a good bit of moisture before it can make it into
the inland southeast. For now, the end of this forecast should be
considered low confidence, and changes will likely be necessary in
future updates as some of the finer scale features come into
better view.

As far as temperatures...maximum and minimum temps will continue to
run about 10-15 degrees above average with an upper ridge in control
over the southeast through the end of the next work week. It should
also be noted, though, that there are some signals for a trend back
towards average just past the end of the current medium range


At KCLT and Elsewhere: Increasing moist lift above a back door cold
front is expected to result in expanding/lowering cigs across the
region through the morning hours. Meanwhile, fog/low stratus will
continue across the mtn valleys through at least sunrise, with at
least brief periods of LIFR, and perhaps VLIFR expected at KAVL. At
the other terminals, cigs are expected to lower to IFR at some point
this morning, prior to sunrise at KCLT, around sunrise at KHKY/KGSP/
KGMU, and by around late morning at KAND. Once the IFR cigs settle
in, they are expected to remain, possibly lowering to LIFR at times,
through the end of the period, as weak cold air damming becomes

For the most part, surface temp/dewpoint spreads appear to be too
high, esp in the face of increasing cloud cover to support much in
the way of fog outside of the mtns. However, MVFR visby will be
featured in most tempos later this morning. Guidance actually
maintains reduced visby through the day, although it`s not at all
clear that this is plausible, so will allow visby to improve to at
least 6SM at most terminals by afternoon.

Outlook: A moist airmass and sfc boundary will remain close to the
fcst area through Thu, with flight restrictions possible each

Confidence Table...

            08-14Z        14-20Z        20-02Z        02-06Z
KCLT       High  94%     Med   78%     Med   73%     Med   77%
KGSP       Med   65%     High  88%     Low   58%     High  91%
KAVL       Med   78%     Med   64%     High  83%     High  89%
KHKY       High 100%     High  97%     Low   55%     High  95%
KGMU       High  82%     High  83%     Low   59%     High  91%
KAND       High  94%     High  83%     High  93%     Med   78%

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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