Area Forecast Discussion
Issued by NWS Greer, SC

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000
FXUS62 KGSP 050249
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
949 PM EST Sun Dec 4 2016

.SYNOPSIS...
A moist wedge of high pressure will remain across the area through
the overnight before a weak cold front crosses from the northwest.
High pressure quickly builds back in while moist air returns late
Monday associated with a low pressure system moving up the Tennessee
Valley. Dry high pressure returns Wednesday and will remain until
another cold front approaches early Thursday.

&&

.NEAR TERM /THROUGH MONDAY/...
As of 940 PM, light rain, with some patchy moderate rain remains
widespread across much of the eastern 2/3 of the forecast area late
this evening, while an ill-defined back edge of this precip has
pushed through much of the Carolina and GA mtns. This back edge
aligns rather well with an H8 trough depicted in short term
guidance. However, occl -RA or DZ will be possible for another
couple of hours, before drier mid/upper level air advects into the
region. Pops have been massaged according to this latest thinking.
Otherwise, the shallow cool pool is expected to continue a gradual
drainage process overnight, as the flow responds to developing
surface low pressure off the Carolina coast. Overnight temperatures
are therefore expected to slowly rise in most locations.

By daybreak Monday pops will be lowered to slight chances north of
I85, with chances south. By that point, model pattern evolution
indicates movement of a deep upper low into south TX, while
another transient surface ridge slides through the OH valley and
begins wedging down the lee side of the Appalachians.  Given that
the moisture stream from the southwest will still exist, am
expecting light upglide induced rain to move in from the southwest
by Monday afternoon, thus pops will comply with likely levels west
of I26 by periods end.  Temperatures will favor a non diurnal trend
given continued southerly llv flow tonight, then trending more
diurnal into the later part of the fcst period.  All in all,
expecting lows to be at or just above normal, with highs at or just
below normal.

&&

.SHORT TERM /MONDAY NIGHT THROUGH WEDNESDAY/...
As of 255 PM EST Sunday: All set for a wet Monday night and Tuesday.
An upper level low over Texas opens up and crosses the area Tuesday.
The surface low along the Texas Gulf Coast takes on a Miller B
pattern and drags a cold front across the area Tuesday as well. High
pressure will be wedged into the area in a cold air damming pattern
Monday night and remain in place until late Tuesday when the cold
front moves through.

PW values increase to 2 standard deviations above normal as the
system moves in. A coupled upper jet will lead to enhanced
divergence and strong synoptic scale forcing. Isentropic lift will
also be impressive as relatively strong low level winds develop as
well. Despite these features, widespread excessive rainfall does not
appear likely given the system`s quick movement. Still QPF values
will range from nearly 1 inch along the TN border to nearly 2 inches
south of the I-85 corridor. This combined with the previous days
rainfall could result in isolated flooding across portions of the
area. With the damming high firmly in place, instability is
virtually non-existent, so any thunderstorms should remain south of
the area. May see breezy conditions across the mountains with the
increasing low level jet, and outside of the mountains in the
stronger ageostrophic NE flow. Lows Monday night will be 10 degrees
above normal, with highs Tuesday near to a little below normal over
the Mountains and 5 to 10 degrees below normal elsewhere.

Precipitation quickly outside of the mountains late Tuesday or early
Tuesday evening as the low pressure system moves east. Lingering low
level moisture and NW flow will keep scattered showers along the TN
border Tuesday night. However, temps will be warm enough for the
precip to be all rain. Dry conditions with some lingering clouds
expected for Wednesday. Lows Tuesday night will be around 5 degrees
above normal, with highs Wednesday near to slightly above normal.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/...
As of 255 PM EST Sunday: The surge of colder air, tied into a strong
cold front, should arrive in our western forecast area Thursday
morning. The front will then quickly cross the region during the day
Thursday. Note, the GFS remains the fastest of the models, while the
European model continues to show a wave on the front, and somewhat
slower progression. We have taken a compromise on the timing, similar
to WPC, with the cold air arrival.

Scattered shower activity will begin to impinge on the mountains of
western North Carolina late Wednesday night and cross the CWA on
Thursday. Fairly good jet structure and just enough moisture/forcing
should justify some POPS during this time frame.

Meanwhile, considering temperature profile, the highest elevations
in the  western North Carolina mountains could mix with snow by
Thursday morning. Frontal showers will move quickly zip across the
region Thursday, while northwest upslope precipitation develops in
the mountains. Our POP structure by the end of Thursday will be back
in the higher terrain to the west.

Upslope snow showers should then persist Thursday night into Friday
morning in the higher terrain. Snow amounts of an inch or so will
certainly be possible near the Tennessee state line and west facing
slopes.

Elsewhere quiet weather conditions are expected Thursday night and
Friday.

We considered going with a hard non-diurnal temperature trend for
Thursday, and went that route but not as aggressively as the GFS
would have. This is taking into account a percentage of the European
model (slower movement) in a blended package.

Coldest air of the season Thursday night through Saturday with
temperatures some 10 to 20 degrees below normal. Below zero wind
chills continue to be advertised in the western mountains Thursday
night and Friday night, with single digits and teens common
elsewhere.

The next problem will be the very end of the weekend potential
precipitation issue. The GFS is on the dry side, while the European
model want to spin up a potential wintry mess Sunday into Monday.
At this juncture we have followed our neighbors, and WPC, with
chance POPS Sunday into Monday. Precipitation types could be a
troubling, but this far out we kept it rain or snow.

&&

.AVIATION /03Z MONDAY THROUGH FRIDAY/...
At KCLT and Elsewhere: Rain chances will gradually taper off at most
terminals through midnight, although -DZ will be possible into the
early morning hours. In the interim, expect IFR to MVFR visby in
mostly -RA and/or BR. With low level moisture remaining abundant in
light NE flow regime, expect deterioration to LIFR cigs prior to
06Z, while IFR visby is also expected to settle in by that time.

As moisture begins to deplete, expect improvement to MVFR by late
morning, with VFR likely developing at most terminals by early
afternoon. However, moisture is expected to begin surging back into
the area from the southwest by the end of the period, with rain
chances and restrictions possibly returning to the Upstate SC
terminals by 00Z Tues.

Outlook: Another round of heavier rain will move into the region
Monday night into Tuesday leading to widespread restrictions. Brief
dry weather is expected on Wednesday, with another front approaching
from the west.

Confidence Table...

            02-08Z        08-14Z        14-20Z        20-00Z
KCLT       High  82%     Low   49%     High  81%     High 100%
KGSP       High  86%     Med   69%     Med   61%     High  96%
KAVL       Med   72%     Med   66%     Med   69%     Med   77%
KHKY       High  82%     Med   66%     High  80%     High  92%
KGMU       Med   78%     Med   69%     Med   69%     High  96%
KAND       High  84%     Med   61%     Med   73%     High  88%

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/JDL
SHORT TERM...RWH
LONG TERM...TS
AVIATION...JDL



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