Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 131758

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
1258 PM EST Tue Feb 13 2018

A cool wedge of high pressure will build in from the north through
today before weakening on Wednesday. Warm high pressure then builds
in from the south to end the work week, bringing a return of well
above normal temperatures. The next front will approach from the
northwest late Friday, cooling temperatures back to near normal and
increasing rain chances again. This unsettled pattern will maintain
some chance of rain most days through early next week.


As of 1245 PM: Cold air damming will remain in place south of a
1045 mb high pressure center now moving into New England. Though
upglide atop the wedging airmass has weakened to the point that
light showers have diminished, a few sprinkles are possible
this afternoon out of the remaining cloud deck. While PIREPs and
satellite imagery indicate the deck is pretty thin, bases have
managed to continue lowering; current expectations are for the
deck to remain pretty solid through the afternoon. Given the lack
of a good scouring mechanism tonight, the more pessimistic sky
cover guidance is favored.

The upper level flow pattern will become increasingly zonal
later today through tonight. Weak embedded waves and an uptick in
moisture should then arrive from the west toward daybreak Wednesday,
especially over the western NC mountains. At the surface, the nose
of the lingering wedge will persist through tonight despite the
deeper layer drying, with the typically small diurnal range on
temperatures expected in the wedge (maxes up to 10 degrees below
climo this afternoon and mins 10 degrees above climo tonight).


As of 300 AM EST Tuesday: The short term begins Wednesday morning as
unsettled weather is expected to consume the forecast period, with a
glimpse of sunshine potentially not in sight under the anticipated
persistence of widespread cloud cover. With nearly zonal flow aloft,
sfc high pressure gradually moving off the NE coast and wedged back
in across the Carolinas is progged to breakdown and detach, allowing
for CAD to slowly erode over the area as guidance highlights the
development of a secondary weak sfc high over the Carolinas. General
consensus remains across the models that this feature will slowly
sink southeastward and move offshore through the day into early
Thursday. With return flow, available moisture will infiltrate in up
through the TN Valley through into the southern portions of the OH
Valley Wednesday afternoon into Thursday. Per analysis, a warm front
or moreso the aid of weak impulses will supply available forcing
across the area, allowing for periods of rain, moreso Wednesday late
afternoon/evening into early Thursday. With upslope flow, have kept
the higher values of PoPs confined to the mountains, decreasing
towards the Piedmont and Upstate. QPFs through the short term will
remain fairly low compared to the recent heavier rainfall this past
weekend, with no flooding concerns expected at this time.

Thursday night into early Friday morning, with lingering light,
isolated showers possible, subtropical ridge will remain in place as
attention turns towards an eastward propagating, deepening upper
trough and a cold front extending from the OH Valley back through
the TN Valley. This feature will just fall short of the forecast
area to the west by the end of the forecast period.

As the wedge breaks down into Wednesday, the infiltration of a
warmer airmass will allow for temperatures to climb into the low 60s
on Wednesday, with cooler spots across the mountains. Overnight lows
will remain above normal. Into Thursday, despite anticipated cloud
cover, temperatures are expected to rise even more into the lower
70s across the Upstate and Piedmont, into the mid to upper 60s/near
70 along and west of the escarpment. These warm temperatures along
with dewpoints near 60 degrees and increasing southwesterly winds,
it most certainly will not feel like a day in early February.


As of 230 AM EST Tuesday: The medium range begins 12Z Friday morning
with the eastern CONUS under the influence of progressive and mainly
zonal upper flow with an upper ridge parked over the Gulf of Mexico.
In the lower levels, a surface cold front will slowly lay across the
southern Appalachians and sag into the southeast by late Friday,
increasing rain chances overnight and into much of Saturday as well.
Another upper shortwave will be transported towards the southeast
late Saturday and into Sunday, and guidance now agrees that the
track will be such that decent Gulf moisture will accompany the
surface reflection of the upper impulse. Rain chances will carry
through Sunday for the entire area as the shortwave passes aloft,
with some of the moisture drawn up into our area possibly
interacting with a weak "in situ" type of high pressure wedge.
Temperatures over the weekend will hover near normal, and with pops
overnight both weekend days in the higher elevations, some brief
snow is reflected in the forecast in our farthest northern mountain
zones. Profiles aren`t very supportive of any impactful winter
weather at this time, so no snow accums were reflected in the grids.

By Monday, the upper Gulf ridge will drift into the Atlantic and
amplify and an upper trough digs into the western CONUS (the
amplitude of which remains a significant point of disagreement in
global guidance). There is general agreement on the idea that there
will be multiple upper shortwaves rounding this upper ridge and
passing over our area Monday and Tuesday, and with a healthy tap of
Gulf moisture established, a surface reflection/frontal
boundary/wave train will slowly lay over our area again, bringing
chances of rainfall through the end of the medium range. With the
upper ridge building off the east coast, heights over our area will
rise aloft early next week, bringing temperatures up to around 15+
degrees above average. Looking just past the current forecast
period, there really isn`t an end in sight to the unsettled/warm
pattern over the southeast.


At KCLT and elsewhere: Weak cold-air damming continues over the
region. A relatively thin cloud deck, mostly at MVFR level, is
expected to linger over most of the area through tonight. Though the
warm upglide that led to this deck`s formation has now weakened,
cigs have continued to lower despite suggestions of some earlier
guidance. The uncertainty is how much, if any, of the deck mixes
out this afternoon. Most likely the deck will hang on until sunset
which suggests no appreciable improvement in cigs until after
daybreak Wednesday. Once the lower deck departs, an approaching
upper level disturbance will bring increasing midlevel cloud cover
for Wednesday, along with small precip chances at some sites.

Outlook: VFR should return Wednesday with dry high pressure
remaining dominant. Unsettled weather, and associated restrictions,
may return later in the week with a cold front approaching from
the northwest.

Confidence Table...

            18-24Z        00-06Z        06-12Z        12-18Z
KCLT       High  91%     High  82%     Med   68%     High  94%
KGSP       High  93%     High  80%     Med   72%     High  81%
KAVL       Med   71%     Med   66%     Med   69%     High  87%
KHKY       Med   74%     High  93%     Low   58%     High  83%
KGMU       High  87%     High  80%     Med   71%     High  82%
KAND       High  93%     High  93%     High  97%     High  90%

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:




NEAR TERM...HG/Wimberley
LONG TERM...Carroll
AVIATION...Wimberley is the U.S. government's official web portal to all federal, state and local government web resources and services.