Area Forecast Discussion
Issued by NWS Greer, SC

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893
FXUS62 KGSP 161457
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
957 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/...
As of 1000 AM EST Monday: Still seeing some pockets of dense fog,
and after sunrise additional dense fog developed across the Upstate
and NE GA, so issued a second SPS for those areas (in addition to
the one out for the mountains). The fog and widespread low clouds
will most certainly mess the temperatures up today with the wedge
front pretty close to the GA/SC state line (but with a wiggle more
into GA on the north side). Made minor adjustments to clouds and
then to hourly temperatures, with an ever-so-slight decrease in
afternoon highs. Other issue is with pops as hi-res models have
backed off late morning precip, though still seem to be on board
with afternoon/evening pops especially across the upslope areas of
the SW mountains with isentropic upglide atop the surface cool pool.
With that, have lowered morning pops and made some hourly
adjustments later in the day, but keeping max daily pops about the
same.

Otherwise, 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 /15Z MONDAY THROUGH FRIDAY/...
At KCLT and Elsewhere: Very little change to the KCLT TAF for the
15z AMD. NE winds continue to prevail with widespread IFR cigs, so
kept previous trend and just adjusted cig heights slightly based on
current obs. Otherwise, expect LIFR cigs to predominate at
KAND/KAVL/KHKY this morning, with mostly IFR at the other main TAF
sites, including KCLT. However, certainly cannot rule out brief
periods of LIFR at those sites as well. With weak cold air damming
established, cigs are expected to remain no better than IFR through
the day.

Cigs are expected to lower again this evening, with LIFR conditions
expected at all terminals by 06Z. More in the way of visby issued
are also expected tonight, with IFR or worse expected at most
terminals after midnight.

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

Confidence Table...

            15-21Z        21-03Z        03-09Z        09-12Z
KCLT       High  85%     Med   66%     Med   65%     Med   77%
KGSP       Med   77%     Med   67%     High  85%     High  94%
KAVL       High  86%     High  84%     High  98%     High  95%
KHKY       High  86%     Med   78%     High  86%     High  92%
KGMU       High  83%     Low   48%     High  82%     High 100%
KAND       Low   58%     High 100%     High  85%     High  98%

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
NEAR TERM...JDL/TDP
SHORT TERM...SBK
LONG TERM...LEV
AVIATION...JDL/TDP



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