Area Forecast Discussion
Issued by NWS Greer, SC

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000
FXUS62 KGSP 142340
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
640 PM EST Sat Jan 14 2017

.SYNOPSIS...
The cool airmass currently in place across the region will erode
on Sunday as the associated surface front lifts north, allowing
well-above normal high temperatures to return. Another cool high
pressure over New England on Monday will force the front south
into Georgia again. The front retreats north again by mid-week as a
cold front approaches from the west. The cold front may stall near
our region late next week allowing rounds of showers to persist
into Saturday.

&&

.NEAR TERM /THROUGH SUNDAY/...
As of 635 PM EST Saturday:  Made a few minor tweaks to pops
accounting for current light shra moving across the northern
mtns/fthills.  Still watching the slow retreat of the wedge front
across portions of the NC/SC Piedmont as winds along/south of
I85 report light vrb/sly at this time.  Still think the front
will move north into the I77 corridor region of lower NC Piedmont
by midnight, then lift further into the I40 corridor overnight.
As such, guidance continues to favor decoupling of the moist BL,
and thus stratus/fog development.  Otherwise, tweaked t/td to
reflect recent ob trends and left the remainder of the fcst as it
was for this update.

At 2 PM Saturday: The upper ridge now over the Southeast USA
will weaken slightly along the east coast tonight and Sunday,
while slight amplification occurs over the lower MS River Valley.

At the surface, ridging along the Eastern Seaboard will break down
overnight, however cloud cover associated with a stalled surface
front is expected to persist over the area. On Sunday another
ridge begins building down the Eastern Seaboard. Precipitation
chances are only expected to increase slightly, from the the NC
Mountains eastward, as low level winds increase, and resultant
lift increases.  Temperatures will remain above normal, with a
slightly greater diurnal range as the ridge weakens, and cool
northeasterly flow veers to the south.

&&

.SHORT TERM /SUNDAY NIGHT THROUGH TUESDAY/...
As of 210 PM EST Saturday: The period begins Sunday night with
excellent model agreement regarding a lifting 500 mb closed low
center over NW TX and a downstream ridge in place over the
southeast. Under the ridge, an 850 mb baroclinic zone will remain
stretched along the northern tier of the forecast area, with
associated weak upglide developing Sunday night into Monday morning.
The upglide will further weaken Monday afternoon as the 850 mb
barocline zone retreats northward, but light southwesterly upslope
forcing may transition the better lingering precipitation chances to
southern/southeastern mountain upslope areas through late day.

Meanwhile, the low pressure system will get gradually absorbed into
a developing longwave trough over the plains Monday. Deeper layer
southwesterly flow will set up over the southern Appalachians Monday
night through Tuesday as the central CONUS trough translates east
toward the lower OH valley. Deeper moisture pooling ahead of the
associated cold front will begin approaching from the west across
western TN/KY through late Tuesday - increasing mountain shower
chances. Anticipate breezy to windy conditions developing over the
high terrain by late Tuesday as southwesterly 850 mb winds increase.

Plenty of clouds are expected throughout the period given the
upglide early, upslope flow late, and continued abundant high clouds
aloft. This will limit insolation, but temperatures will continue
above climo through the period, and surge well above climo in the
solidly warm sector air by Tuesday.

&&

.LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/...
As of 235 PM Saturday, Guidance remains in disagreement through the
medium range keeping confidence low. The GFS remains faster with the
Wednesday cold front and associated upper low. The ECMWF remains
slower. They do agree on a ridge building in on Thursday behind this
system. However, on Friday the ECMWF takes an upper low through the
bottom of the ridge and across our area, while the GFS moves the
ridge axis east and moves some short wave energy over the area in
the SW flow.

Therefore, both models agree on precip over the area Tuesday night
with the GFS drying things out quickly Wednesday and remaining dry
Thursday. The ECMWF has precip through the day Wednesday. It also
stalls the front over the area with a wave of low pressure forming
to the west and moving along the front bringing more precip on
Thursday. Model blend and national guidance suggests moving toward
the wetter solution, so have done that. However, have all PoP but
Tuesday night in the chance range given the uncertainty. Lows
Tuesday night around 20 degrees above normal fall to around 15 above
normal Wednesday night. Highs will be 10 to 15 degrees above normal
both days with Thursday being slightly cooler.

Both models keep precip over the area Friday and Saturday, but
differ in the overall pattern. The GFS brings a warm front into the
area Friday and a cold or occluded front on Saturday. The ECMWF
brings a warm front in, but then brings a wave of low pressure along
the front across the area Saturday. Again, a model blend and
national guidance keeps low end chance over the area each day. Lows
Thursday night will be just under 20 degrees above normal rising to
just above 20 degrees above normal for Friday night. Highs both days
remain nearly steady 10 to 15 degrees above normal.

&&

.AVIATION /00Z SUNDAY THROUGH THURSDAY/...
At KCLT and Elsewhere: MVFR/IFR and LIFR expected to some degree at
all sites through this taf period as a high pressure wedge slowly
erodes to the northeast overnight.  However, light surface flow
amongst a decoupling/moist BL will lead to low stratus/fog at all
sites tonight, therefore all tafs features some flavor of said
restrictions with adjustments based upon guidance.  Winds are a
little tricky to start as all Upstate sites seem to be just south
of the retreating wedge front, and thus are reporting sly flow,
while the NC sites remains light vrb/nly.  Thus, opted to initialize
KCLT/KHKY with a nly wind through late evening, then veered sly
and light for the overnight hours.  Beyond that, conditions are
expected to improve at all locations through late morning Sunday,
eventually leading to low VFR conditions by the afternoon, all
before another wedge front approaches from the northeast.  Lastly,
did include precip mention at KAVL/KHKY with timing based upon
latest radar trends, and near term guidance for Sunday.

Outlook: Cool high pressure ridges down the East Coast Sunday
evening, bringing yet another round of precipitation and
restrictions to start the work week.

Confidence Table...

            23-05Z        05-11Z        11-17Z        17-18Z
KCLT       Med   72%     Low   38%     Med   65%     Low   56%
KGSP       High  83%     Low   26%     Low   55%     Low   56%
KAVL       High  83%     Low   55%     Med   70%     Med   65%
KHKY       High  83%     Low   21%     Med   65%     Low   56%
KGMU       High  83%     Low   36%     Low   38%     Low   56%
KAND       Med   78%     Low   21%     Med   70%     Low   56%

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...JMP
NEAR TERM...CDG/JAT
SHORT TERM...HG
LONG TERM...RWH
AVIATION...CDG



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