Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 142349

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
649 PM EST Thu Dec 14 2017

Dry and cool high pressure will dominate our weather through Sunday
morning. Weak southerly flow with limited moisture will return to
the area Sunday and Monday as another cold front approaches from the


As of 630 PM Thursday: A dry cold front will continue to sag
southward acrs the balance of cwfa tonight. Evening IR satellite
imagery still shows considerable high clouds along the periphery of
the cwfa, but little else atop the region.  Considerable high clouds
along and south of upper jet axis will spread northward tonight in
concert with the approach of elongated positive tilt upper trough.
Sensible weather overnight should be limited to mainly considerable
high clouds.  At this point, encroaching clouds may hinder
temperature drop overnight, in fact progged mins on latest guidance
is a few deg F less cold than going fcst. Will monitor this trend
through mid-evening before making any temperature changes.

On Friday, another shortwave will push across the Great Lakes/Ohio
Valley through the day, but will remain north of the forecast area.
Thus, expect quiet weather conditions with passing clouds and high
temperatures just below normal.


As of 215 PM EDT Thursday: A split flow pattern will set up over the
southern half of the CONUS by Friday evening, with a northern stream
clipper system moving from the southern Appalachians to the mid-
Atlantic/southeast coast while deep, closed low pressure sets up
over Mexico. Dry profiles will persist over our forecast area
through Saturday as a flat upper ridge develops over the southeast,
with temperatures near climatology. Meanwhile, the southern tier
system will open up and phase through west TX. This system will lift
over the Ohio Valley through Sunday as yet another southwestern
cutoff low develops somewhere from Arizona to the Baja Peninsula.
Mid level moisture will begin returning from the southwest ahead of
the first phasing system Saturday night, but any deeper moisture
will be slow to arrive through Sunday. Any early Sunday morning
onset of light precipitation in the far southwest mountains could be
freezing rain, but onset prior to temperatures warming above
freezing looks unlikely.


As of 235 PM EST Thursday: Guidance is coming into better agreement
on the overall pattern through the medium range. However, some
detail differences remain keeping the overall forecast confidence on
the low side. Upper ridging over the southeast CONUS Monday moves
east Tuesday as split stream troughs move east toward the area. The
GFS is faster with the troughs keeping both streams relatively in
phase and moving east of the area Wednesday. The ECMWF moves the
northern stream trough to the east with similar timing as the GFS
but is slower with the southern trough and actually has a secondary
southern stream trough late on Wednesday. The GFS troughs, while not
particularly strong, are stronger the troughs on the ECMWF. A wave
forms along a frontal boundary stalled to our south Monday which
spreads moisture and precip north into the area. A stronger cold
front moves into the area Tuesday and to the east Tuesday night.
This should bring a better chance of precipitation, but even that
could be limited as moisture flux may be interrupted by convection
along the stalled front to our south. Therefore, have limited highest
PoP to good chance given the uncertainty. Looks like precip will be
all rain as H85 temps and thicknesses are warm for this time of
year. Some mountain valleys could be in the 30s but should remain
above freezing throughout. There could be some lingering NW flow
precip Tuesday night across the mountains, but even this ends before
temps cool enough for snow to mix in. Temps should be above normal
all locations.

Dry high pressure and upper ridging build into the area Wednesday
and Thursday. Another trough and frontal system build over the
middle of the CONUS by late in the period, but expect any precip to
hold off until after this forecast period, especially since there is
timing disagreement with this system. Temps cool a little but remain
above normal.


At KCLT and Elsewhere: Expect VFR through the valid TAF period.

A dry cold front will will sink south of the FA tonight allowing
light northerly winds to develop acrs the balance of the FA.
Winds just above the sfc will back to the southwest as well, ,
allowing for low-level moisture to infiltrate into the northern half
of the FA. Moisture progged around 850mb remains sparse and areas of
FEW-SCT040 may still develop. For the daylight hours on Friday, a
westerly sfc flow will be seen, perhaps gusty in the mountain as
well.  Clouds will be limited to considerable high clouds.

Outlook: Potential for short-lived restrictions on Sunday with rain
showers. Otherwise, expect VFR as a series of dry cold fronts move
through the area.

Confidence Table...

            15-21Z        21-03Z        03-09Z        09-12Z
KCLT       High  81%     High  82%     Med   68%     Low   56%
KGSP       Med   70%     Med   75%     High  83%     Med   64%
KAVL       High  94%     High  85%     Med   70%     High  87%
KHKY       High 100%     High  83%     Med   66%     High 100%
KGMU       Med   76%     High  86%     High  85%     Med   63%
KAND       Med   76%     Med   65%     High  90%     Med   61%

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:




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