Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 032025
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
325 PM EST Sat Dec 3 2016

.SYNOPSIS...
Increased moisture will return from the west on Sunday and linger
into Tuesday. A strong cold front will arrive early Thursday
bringing some of the coldest air of the season so far at the
end of the week.

&&

.NEAR TERM /THROUGH SUNDAY/...
As of 130 PM EST Saturday:  A closed H5 cyclone centered over NW
Mexico continues to deepen as moisture lifts n/ne across the MS
Delta region into the the TN/OH valleys.  Surface high pressure
remains centered over the southern/central Appalachians this
afternoon and thus reinforcing a dry llv airmass.  However, given
the aforementioned moisture advection and swly flow aloft, the atm
will moisten with time from the top down.  As such, latest vissat
imagery indicates modest amounts of mid/high altocu/cirrus streaming
into northeast GA and the southern Appalachians at present time.
This pattern will continue into the evening/overnight with pops
increasing later this afternoon from the west with likely levels
favored west of I77 by 12z, then spreading across the entire fcst
area by midday Sunday.

Profiles across the region during this time frame so support all
ra with the exception of higher terrain locales above 4-5kft.
For those areas, expecting ptype phase changes from ra by early
morning to ra/sn or all sn by mid/late morning, especially across
the northern mtns.  Some light accumulations are possible in this
region, however generally less than 1 inch.  Temperatures will
slowly warm into late morning across the entire fcst area leading
to all ra by midday as highs top out in the upper 30s across the
mtns to upper 40s over the Piedmont.  Rainfall amounts through
Sunday afternoon are fcst to be around 1-1.25 inches across
the southwest/central NC mtns and northeast GA, tapering down
to the east with a half to quarter inch favored at GSP and CLT
respectively.

&&

.SHORT TERM /SUNDAY NIGHT THROUGH TUESDAY/...
As of 215 PM EST Saturday: A split flow pattern early in the period
evolves into a single flow Atlantic ridge and broad central and
western CONUS trough by the end of the period. The northern wave of
the split flow on pushes a frontal boundary across the area. The
combination of deep moisture and synoptic scale lift, along with
isentropic lift, will spread rain across the area through the night.
Although surface temps across the Northern Mountains will be in the
mid 30s overnight, a nearly 10 degree C low level warm nose will
keep precip as all liquid. Lows will be around 5 degrees below
normal. QPF values will range from tenth to a half an inch from
north to south.

The moisture and lift move east and south of the area early Monday
as high pressure builds in from the north and sets up in a cold air
damming pattern. As this takes place, the southern stream upper low
over the Rio Grande opens up and moves across Texas. Short wave
energy moves through the flow ahead of the low and across our area.
The associated surface low moves east along the Gulf Coast spreading
a moist southerly flow across the SE CONUS. Precip spreads back into
the area from the SW in response. QPF will be light. Temps will be
tricky with the damming high setting up, but precip tapering off
across portions of the area. Expect highs generally in the low to
mid 50s, but they could be higher where precip ends and lower where
it lingers.

Precip develops in earnest Monday night as the upper low tracks into
MS and the surface low takes on a Miller B pattern. Deep moisture
returns, along with strong synoptic and isentropic forcing. This
will strengthen the damming high across the area. As the surface
lows track east on Tuesday, the southern wedge boundary does lift
north toward the area. However, expect it, and any resulting
instability or thunderstorms, to remain to our south as well. Still,
given the PW values and strength of the forcing, expect QPF values
to range from around 0.75 inches near the TN border to 1.5 inches
along the southern tier of the CWFA. Lows Monday night will be
around 10 degrees above normal with all liquid precip. Highs will be
near normal across the mountains where the damming influence is
less, to around 5 degrees below normal elsewhere.

&&

.LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/...
As of 245 PM EST Saturday: A surface boundary should be south of our
county warning area (CWA) Tuesday evening as a deamplifying upper
level trough and vort max quickly sweep northeast into Virginia.
This will allow any lingering POPS to end quickly in the evening.

Wednesday a rather non descript pattern as the atmosphere reloads to
the west, and the surface pattern across our region remains "baggy"
with a weak flow. Conditions should remain dry for the balance of
the day.

A strong H5 trough will rotate into the middle Ohio Valley Wednesday
night and Thursday, signaling a change in our weather pattern. This
will allow a shot of cold air to begin a plunge into the region.
Thermal structure continues to show a downward trend in thickness
and H85 temperatures from late Wednesday night through Thursday -
at least.

We will continue with low POPs from late Wednesday night into the
wee hours Thursday night - with weak vorticity advection/cold air
advection and a bit of moisture. Deepest moisture should be in our
North Carolina mountains. Speaking of our North Carolina mountains
it appears to be cold enough for a change to all snow showers,
although precipitation amounts should be light at the moment.

Cold high pressure will then build into the region Friday and
Saturday.

Temperatures around normal Wednesday will start a much colder trend
in the Thursday through Saturday time range, perhaps some 10 to 15
degrees below normal.

&&

.AVIATION /21Z SATURDAY THROUGH THURSDAY/...
At KCLT and Elsewhere:  A mixture of VFR/MVFR and possibly IFR is
expected through this taf cycle as moisture advects into the region
from the southwest.  A deepening system moving through northern
Mexico will continue to loft moisture ne over the southern states
through the period.  As such, am expecting said moisture to lift
isentropically atop a broad region of high pressure. This will
result in increased chances for ra into/thru the overnight with
cigs/visb falling into restrictive flight categories.  These
restriction levels and timing in the tafs are based upon latest
CAM guidance and fcst soundings.  Once conditions deteriorate,
restrictions are favored at all sites through the period.
Winds will remain light vrb this afternoon, possibly veering sely
at the Piedmont sites to include KCLT, then should back nly for
the remainder of the taf cycle.

Outlook: Moisture will gradually spread into the region through
Sunday leading to increasing chances for precipitation and
restrictions. A brief lull is possible Monday with the best chance
for heavier rain and widespread restrictions on Tuesday. Brief dry
weather on Wednesday, with another front approaching from the west.

Confidence Table...

            20-02Z        02-08Z        08-14Z        14-18Z
KCLT       High 100%     High 100%     High  83%     High  93%
KGSP       High 100%     High 100%     High  88%     High  98%
KAVL       High 100%     High 100%     High  89%     High  85%
KHKY       High 100%     High 100%     High  90%     High  90%
KGMU       High 100%     High 100%     High  87%     High  98%
KAND       High 100%     High  95%     High  86%     High  97%

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...SBK
NEAR TERM...CDG
SHORT TERM...RWH
LONG TERM...TS
AVIATION...CDG



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