Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 140538
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
1238 AM EST Sat Jan 14 2017

.SYNOPSIS...
Cool high pressure ridges down from New England today as a
stationary front remains over Georgia. This high pressure moves out
over the Atlantic tonight and Sunday as the front moves north over
North Carolina on Sunday. Another cool high pressure over New
England on Monday will force the front south over Georgia again. A
cold front will approach our region from the west through mid week
as well above normal temperatures prevail ahead of the front.

&&

.NEAR TERM /THROUGH TODAY/...
1230 AM EST Update...made some lowering adjs to the going pops based
on the latest WSR-88D trends and good consensus among the short
range hires models. Overcast skies have held y/days above normal
temps 6-8  higher than the fcst curve...so will adj up across
localized areas.

As of 1030PM EST Friday:  As expected, light upglide induced
precipitation is now starting to develop across portions of the
northern NC Piedmont, while a few residual light showers struggle to
survive along the frontal boundary which is now pushing south of the
I85 corridor.  Guidance favors weaker upglide for this southern tier
of the fcst area, while the aforementioned NC Piedmont zones will
likely see light showers all night.  Thus, did increase and spread
out likely/categorical pops along the I40 corridor, east of the NC
mtn zones.  Given increased low/mid stratus, latest minT guidance
has come in a bit warmer than previously progged, therefore did
blend in consshort which effectively increases minimums around a
degree or two beneath the intruding wedge.  Otherwise, no additional
adjustments were needed/made with this update.

Previous Discussion: Saturday will be cloudy and considerably
cooler as a back door cold front/wedge front with a cold pool and
dense low clouds behind it flows across the area from northeast to
southwest tonight and Saturday morning.  Some light, stratiform
precip is also nicely depicted by high-res models behind the
front through Saturday morning.  With clouds and cool-advection,
Saturday temps. will have a narrow range from the upper 40s for
lows in the mountains to upper 50s for highs in Piedmont areas.

Parent surface high that supports northeasterly cool flow behind
front Saturday morning gradually dissolves Saturday afternoon and
dense low clouds associated with cool pool behind the front may
begin to erode Saturday afternoon or evening, with Sunday seeing
a warm-up back to above normal temps.

The balance of Friday will continue with increasing clouds and
light winds, and a few isolated light showers, with denser low
clouds coming with the back door front early Saturday morning.
Some showers aided by westerly 850mb flow along the Southern
Appalachians will continue this evening, being joined by some light
showers behind the back door front later.  Upper flow remains zonal,
with a large upper high over FL and the Gulf Coast.

Some marginal convective instability has developed over western
parts of the CWA with MUCAPE to 250 j/kg.  Current radar and
satellite do not show any convective activity so far, beyond some
low-top stratocu.  However, some of the widely scattered showers
could become stronger over the next few hours before diurnal
cooling rapidly eliminates this marginal instability.

&&

.SHORT TERM /TONIGHT THROUGH MONDAY/...
As of 200 PM EST Friday: A flat upper level ridge will be in place
across the southern tier of the central and eastern CONUS the latter
half of the weekend as a deep, closed low lifts from western Mexico
across West Texas. Deeper moisture feeding east of this system will
spill over the northern periphery of the ridge and stretch out close
to western North Carolina Saturday night into Sunday before
retreating northward Sunday night. Meanwhile, at the surface, weak
cold air damming may still be in place Saturday evening. The wedge
boundary will begin a period of oscillation, with some northward
movement through Sunday and then a possible backdoor retreat into
the area once again Sunday night as surface high pressure slides
east from the Great Lakes to the East Coast. Forcing over the
oscillating wedge appears quite limited during the period, but any
chance of weak moist upglide will be best over western NC.

A highly amplified pattern will remain in place on Monday with the
reinforcing trough axis gathering over the plains states while a
ridge builds over the southeast. Transient northern tier upglide may
continue into Monday and this could help pull the wedge boundary
back southward across our region. Any QPF through the period will be
light. Temps should see a smaller diurnal range across the more
wedge-impacted northern tier and more warming and less precip threat
across the southern tier.

&&

.LONG TERM /MONDAY NIGHT THROUGH FRIDAY/...
As of 240 PM Friday, confidence has taken a hit for the medium range
as models are in flux with the potential weather systems moving
through the area. The ECMWF keeps the upper ridge over the eastern
CONUS in place on Tuesday while the GFS has it weakening. This
allows an upper low to cross the Great Lakes Tuesday night with its
trailing trough to cross our area late Tuesday night and early
Wednesday. The ECMWF brings the trough through late Wednesday and
early Wednesday night. The ECMWF keeps the flow zonal for Thursday
with a dampening short wave crossing the area. The GFS shows flat
ridging with a weak short wave. Both models show a progressive upper
low crossing the area Friday, but the ECMWF shows it weakening while
the GFS is stronger.

At the surface, the damming high over the area weakens Tuesday as a
cold front approaches from the west. The ECMWF brings the front into
the area Wednesday while the GFS moves it through Tuesday night. The
ECMWF stalls the front just to our south through Friday with some
weak moisture return and precip over the front. The GFS is dry for
Wednesday and Thursday with moisture and precip returning late in
the day on Thursday and continuing into Friday in developing low
level southerly flow. Given all these differences, have gone with a
mix of guidance blend and national center guidance. This means
slowly increasing PoP Tuesday and Wednesday. PoP drops off a little
Thursday into Friday but remains in the chance range. There is also
little to no agreement on whether any thunderstorms can develop, let
alone severe storms.

Highs 5 to 10 degrees above normal Tuesday rise to 10 to 15 above
normal for Thursday and Friday. Lows Monday night 15 to 20 degrees
above normal rise to around 20 above normal for the rest of the
period

&&

.AVIATION /06Z SATURDAY THROUGH WEDNESDAY/...
At KCLT/KHKY: A llvl wedge will build in and slowly breakdown late in
the TAf period. There wont be much isent lift over the cold
dome...however enuf prevailing moisture will be available to produce
sct -shra over the fthills and piedmont regions. The hires models
agree on a very limited qpf response. Thus...pops were cut back
and went with vcsh thru the morning hrs at both locales. Cigs shud
drop into the MFVR range at KCLT and possibly TEMPO IFR arnd
daybreak. Expect MVFR/IFR KCLT/KHKY thru most of the day Sat as w/ly
h92-h85 flow develops aft 18z.

Elsewhere:  KAVL will see decreasing cigs and vsby overnight into
the MVFR/IFR range as moisture is maintained associated with wafting
ern wedge front moisture. The same trend will occur across the
Upstate sites. Don/t see much chance for precip across these sites
with limited lift...but perhaps very brief -shra or vcsh. MVFR to
IFR cigs will persist thru most the taf period over the Upstate
sites with downsloping flow developing btw 18z-20z. KAVL may
retain low cigs thru the period as moisture atop the shallow
cold pool is slow to modify across the valleys.

Outlook: Cool high pressure ridges down the East Coast over the
weekend, bringing chances for precipitation and restrictions.

Confidence Table...

            05-11Z        11-17Z        17-23Z        23-00Z
KCLT       High 100%     High 100%     High 100%     High 100%
KGSP       High 100%     High 100%     High 100%     High 100%
KAVL       High 100%     High  89%     High 100%     High  94%
KHKY       High 100%     High 100%     High 100%     High 100%
KGMU       High 100%     High 100%     High 100%     High 100%
KAND       Med   60%     High  94%     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...None.
SC...None.

&&

$$
SYNOPSIS...HG
NEAR TERM...CDG/SBK/WJM
SHORT TERM...HG
LONG TERM...RWH
AVIATION...SBK



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