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000
FXUS62 KGSP 090848
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
348 AM EST Mon Dec 9 2019

.SYNOPSIS...
The weather will be unsettled, with occasional rain until a cold
front passes east of the region Tuesday night and early Wednesday.
Rain is forecast to briefly change to snow before ending across the
North Carolina mountains early Wednesday. Dry but cold high pressure
will settle in behind the front for mid-week, with another storm
system expected to bring precipitation late in the week.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 250 AM: Expansive sfc high pressure is centered off the
Atlantic coast. Water vapor imagery depicts a shortwave swinging
from the Rockies into the northern Plains, and low pressure is
developing in the Midwest as a result. Closer to home, a lobe of
the offshore high extends inland over the Carolinas, manifesting
as a wedge. Dewpoints are mostly in the 20s attm, with temps
largely in the lower 40s. The Midwest low is already associated
with a broad area of warm advection across the Southeast, and as
the warm conveyor belt moves across the area today, precip should
result atop the wedge, reinforcing it via evaporative cooling.

Model QPF reflects a significant boost to the lift in the upslope
areas, which means PoPs only reach the likely range near the
south-facing terrain. In fact, as the better midlevel winds
exit to the east and north late in the day, the net forcing may
diminish enough away from the Escarpment that a lull in precip
will occur. However, with the potential for at least sprinkles or
the occasional shower to occur, a small PoP has been retained in
most areas. The temp fcst will largely hinge on the expectation
of evaporative cooling; the NAM as usual reflects this very
strongly. However, with the parent high being so far offshore,
it is a little questionable how effective the wedge will hold on
in areas that see less rainfall. Virtually all guidance, even the
NAM, brings sfc winds around to the south today, and this could
easily bring temps well above normal if the wedge were not in
play. Normally our short-term model consensus product does very
well with wedge temps, and it depicts the warmer air making it
about as far north as I-85. I did blend in a bit of the NAM`s
temps, sharpening the gradient between "fully wedged" temps near
the Blue Ridge and north of I-40, and above-normal values in the
far southeast. The retreat of the wedge boundary likely will lead
to lowering ceilings and possibly areas of fog near the boundary,
as the airmass becomes very shallow.

The sfc high will move east of Lake Huron by 00z, leading low to
midlevel winds to veer, and drier air will advect in above 850
mb. The more westerly winds will be associated with a loss of
the WAA and possibly even the onset of CAA at some levels. While
mostly cloudy to overcast conditions should continue, PoPs will
remain largely at slight-chance away from the better terrain
thru the evening. As the cold front nears in the early morning,
the westerly flow will strengthen and further increase chances in
the SW NC mountains and vicinity. Tonight`s min temps generally
will occur in the early evening, as the wedge loses its grip.

&&

.SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/...
As of 250 am Monday: The leading edge of a rather well-forced/moist
cold front will begin to pass through the forecast area near the
start of the short term period...moving somewhat slowly across and
east of the area by Tue evening. With strong upper jet axis
displaced well behind the front, much of the forcing/moisture will
be found along and on the cold side of the boundary. Pops therefore
increase gradually to categorical across the northwest half of the
CWA by the end of Tuesday, reaching a nadir with 80-90 pops across
the entire area Tue evening. Event total rainfall amounts will be
rather tame...generally .5-1.0 inch in most areas, except across the
high terrain of southwest NC, where 2-3 inches are possible.

The anafront nature of this scenario will create p-type concerns
across mainly the NC mtns Tue night/early Wed, as cold air is
expected to overspread the area while moisture and forcing are still
in place (at least to some degree). Forecast soundings suggest a
narrow transition zone to sleet and/or freezing rain will exist, but
the bulk of precip wintry precip would most likely fall as snow.
It`s always tricky to nail down accums in these anafront events, and
they tend to have a tendency to "disappoint," but current
indications are that an inch or two will be possible across the TN
border counties, with amounts likely tapering down quickly to little
more than a dusting across the interior mountain counties. Surface
should be quite warm before the transition to snow occurs, so accums
would most likely be confined to grassy surfaces. Winter wx
headlines are certainly not warranted at this juncture  (and may
never be with this event), but we will begin to mention this event
in the HWO and briefing materials.

The remainder of the short term will see quickly drying conditions
Wed morning, with chilly weather expected Wed into Wed night, when
temps are forecast to be roughly 5 degrees below normal.

&&

.LONG TERM /THURSDAY THROUGH SUNDAY/...
As of 330 am Monday: A rather progressive upper air pattern will
result in unsettled weather during much of the medium range, as a
series of short wave troughs are forecast to interact with a
baroclinic zone draped across the Southeast. The extended period
will begin dry and cool, but pops will gradually ramp up late Thu
into Friday, during which time moisture and upglide associated with
a developing Gulf Coast surface wave are expected to overspread the
Southeast. Owing to the cool and dry conditions, and precip falling
Fri morning could fall as light freezing rain, mainly across the
mountain valleys near the Blue Ridge and along the I-40 corridor in
the Piedmont and foothills. While light accums cannot be ruled out,
and pronounced in-situ/hybrid cold air damming will likely develop
in response to any falling precip, current guidance indicates that
parent surface high pressure will be in an unfavorable location to
lock in sub-freezing temps for any significant length of time. Thus,
a quick transition to rain is forecast by Fri afternoon. Likely pops
will otherwise be advertised by Friday afternoon, continuing into
Saturday before slowly tapering off late Sat/Sat night.  Dry
conditions should return by Day 7. Temps will begin the period below
normal, possibly ending up well below normal under Friday`s cold air
damming regime, then return to above-normal levels by Day 7.

&&

.AVIATION /09Z MONDAY THROUGH FRIDAY/...
At KCLT and elsewhere: Within an strengthening and increasingly
moist warm-advection regime, areas of -DZ will occur this
morning. Continued development of precip, associated with LLJ into
Great Lakes low pressure, warrants addition of -SHRA to the TAFs
later this morning, and is expected to promote a cool in-situ
wedge. Cigs will lower especially as precip becomes steadier,
but likely won`t go IFR until after daybreak. The strong winds
aloft imply a LLWS threat for most of the period. Wedge front is
expected to creep northward later in the day, likely introducing
LIFR if it has not already formed. Weakening flow aloft will
reduce precip rates late in the day, but areas of LLWS remain in
the fcst. Little to no improvement expected after sunset.

Outlook: Widespread restrictions along with occasional rain are
expected to persist thru at least early Wednesday. A cold front
slips into the area on Tuesday, but drier air doesn`t filter in
until Wednesday. Dry high pressure should return during midweek
and is forecast to persist through at least Thursday.

Confidence Table...

            08-14Z        14-20Z        20-02Z        02-06Z
KCLT       High  85%     Med   77%     High  80%     Med   68%
KGSP       High  90%     Med   75%     High  80%     Med   76%
KAVL       Med   68%     High  95%     Med   75%     High  90%
KHKY       High 100%     Med   66%     Med   61%     Med   78%
KGMU       High  90%     Med   70%     High  83%     Med   73%
KAND       High  88%     High  90%     High  80%     Med   75%

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...JDL
NEAR TERM...08
SHORT TERM...JDL
LONG TERM...JDL
AVIATION...08