Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 240511
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
1211 AM EST Tue Jan 24 2017

.SYNOPSIS...
A strong upper level low will move northeast of the region before
warm high pressure builds into the region through late Wednesday. A
cold front will push east of forecast area Thursday...with below
normal temperatures returning Friday through the weekend.

&&

.NEAR TERM /THROUGH TODAY/...
As of 1210 AM EST Tuesday:  Tweaked pops up to slight chance
levels across the NC/SC Piedmont and Fthills through early morning
given light moisture wrapping around the departing upper cyclone.
Otherwise, the current fcst remains on track with this update and
only minor adjustments to t/td trends were needed/made.

As of 225 PM EST: Water vapor imagery shows the closed upper low
center moving east across the central Carolinas piedmont, with
surface observations indicated the pressure falls near coastal North
Carolina. This system will continue to slowly pivot away to the east
through late day, with lingering deformation zone forcing moving
east across the I-77 corridor through late afternoon. Elevated PoP
values will follow this area of deeper moisture and forcing. As the
banded forcing slides farther east, northwest flow upslope forcing
and moisture will increase across the western mountains this evening
and overnight. Thermal profiles continue to support mainly rain
across the mountains, however, snow levels should continue to fall
across elevations above about 4000 to 5000 feet. This should allow
the higher ridges to see some light snow accumulations through
the overnight areas, but any advisory level accumulations would
be mainly at 5000 feet and up - with upwards of 3 inches possible
around the Smokies. No Winter Advisory products appear needed given
the very high elevation nature of any accumulations. In addition,
the low level cold advection jet during the peak of the northwest
flow may reach around 50 kt along the Blue Ridge toward daybreak.
The surface based mixed layer should just briefly the strong winds
near the Blue Ridge, so we high end advisory criteria still looks
good there. Any uptick in the 850 mb cold advection jet overnight
could require a small High Wind Warning near the northern Blue
Ridge.

The 500 mb low center will move east off the Mid-Atlantic
coast overnight, with broad ridging building over the southern
Appalachians from the west through Tuesday. NW upslope moisture will
steadily dry up as well through the day on Tue with mountain winds
diminishing after Noon as the pressure gradient relaxes. Expect
lee troughing to develop east of the mountains through Tuesday
afternoon. Downsloping off the mountains should yield plenty of
max temps in the 60s over the foothills/piedmont Tuesday afternoon.

&&

.SHORT TERM /TONIGHT THROUGH THURSDAY/...
As of 245 PM EST Monday: High pressure will be across the area on
Tuesday night. That feature will pull away on Wednesday as the next
in a series of systems impacts the region. Temperatures in the
southwesterly flow will top out around 70 outside the mountains
Wednesday afternoon.

A cold front will push across the region Wednesday night. A band of
showers is expected with this feature. Amounts look to be a quarter
to a third of an inch in the mountains and around a tenth of an inch
in the Piedmont.

The front will push east of the region on Thursday leaving most of
the area dry and a bit cooler. Northwest flow showers will develop
along the Tennessee border by Thursday afternoon. The showers will
be snow in the higher elevations and rain lower down with a gradual
trend to more snow by late in the day. Little accumulation is
expected.

&&

.LONG TERM /THURSDAY NIGHT THROUGH MONDAY/...
As of 230 PM Monday...looks like a return to winter for the western
Carolinas and northeast Georgia at the end of the week, not so much
because of precipitation, but in terms of temperatures. We have been
anticipating an upper pattern change for the end of the month and
the new guidance continues to show a mean upper trof over the
eastern half of the country for the period from Friday onward to the
end of the 10-day model runs, with perhaps a brief break in the
middle of next week. The mean upper trof axis should be centered
over land for most of the period, which should afford us the passage
of several weak short waves dropping down into the trof and more
than one surge of low level moisture from the north/west. This bodes
well for the chances of snow near the TN border, but the timing of
any periods of better probability are difficult to nail down because
of timing differences between the GFS and ECMWF.  Suffice to say
that we should expect more than one NW Flow Snow event during the
medium range period, the first of which may be underway Thursday
night and into Friday morning. The GFS in particular shows moisture
surges Friday evening, then another Saturday afternoon, and a third
Sunday night and Monday. The ECMWF is not as impressed with
magnitude and duration. The forecast more or less follows the idea
of the operational GFS, while limiting precip to the lower part of
the chance range due to uncertainty this far out in the forecast. No
precipitation is expected east of the spine of the Appalachians.
Temps should be at or slightly below normal. The last surge on
Monday could be the interesting one, as the GFS shows a stronger
short wave with a vort center diving down and crossing northeast
GA/Upstate SC in the afternoon with a deep cold air mass in place.
This sort of mid/upper feature is typically what we need to cause
some of the snow showers/flurries to break containment and move out
east of the Blue Ridge. It is way too far in the future to start
including chances of snow outside the mtns, but it is fair to say
there is a non-zero chance of wintry precip as seen in fcst
soundings from the GFS over the NC Piedmont/Foothills and GEFS plume
diagram at CLT on Monday. This will hold some of our interest going
forward.

&&

.AVIATION /05Z TUESDAY THROUGH SATURDAY/...
At KCLT and Elsewhere:  VFR conditions will prevail at all sites
through this taf cycle with the exception of at KAVL where MVFR
low stratus is possible consequent of upslope shra/shsn along the
TN line.  An upper low continues to move away from the region,
while moisture wraps around the western flank.  Thus, light shra
is possible over the next few hours at all NC sites, as well as
at KGSP/KGMU.  Therefore all these sites feature vcsh and tempos
for -shra.  Cigs continue to improve from the southwest as drier air
advects in, thus am expecting current bkn low stratus to gradually
sct out to mid/high levels as sunrise approaches, possibly going
skc into the afternoon.  Otherwise, winds will remain wnwly through
the period with gusting possible this afternoon.

Outlook: Dry conditions are expected into Wednesday.  Brief moisture
return is possible ahead of the next cold front Wednesday night
into Thursday, with colder air and NW flow moisture setting up by
late week into the weekend.

Confidence Table...

            05-11Z        11-17Z        17-23Z        23-00Z
KCLT       High  81%     Low   53%     High 100%     High  89%
KGSP       Med   75%     Med   61%     High  87%     High 100%
KAVL       Med   62%     Med   72%     High  87%     High  89%
KHKY       Med   62%     Med   78%     Med   62%     Low   36%
KGMU       High  81%     Med   66%     Med   62%     High 100%
KAND       High  94%     High  83%     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:

www.weather.gov/gsp/aviation

&&

.GSP WATCHES/WARNINGS/ADVISORIES...
GA...None.
NC...Wind Advisory until noon EST today for NCZ033-048>053-058-059-
     062>065-501-503-505-507-509.
SC...None.

&&

$$
SYNOPSIS...SBK
NEAR TERM...CDG/HG/JAT
SHORT TERM...SW
LONG TERM...PM
AVIATION...CDG



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