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000 
FXUS62 KGSP 160824
AFDGSP

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

.SYNOPSIS...
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.

&&

.NEAR TERM /THROUGH TONIGHT/...
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 
area. 

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.

&&

.SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/...
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. Meanwhile...an 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.

&&

.LONG TERM /THURSDAY THROUGH SUNDAY/...
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
forecast.

&&

.AVIATION /09Z MONDAY THROUGH FRIDAY/...
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 
established.  

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 
day.

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:

www.weather.gov/gsp/aviation

&&

.GSP WATCHES/WARNINGS/ADVISORIES...
GA...None.
NC...None.
SC...None.

&&

$$
SYNOPSIS...LEV

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