Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 171038

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
638 AM EDT Tue Oct 17 2017

Dry conditions and below-normal temperatures will persist through
mid-week. Warmer temperatures will return later this week as
deep-layer ridging sets up over the southeastern states.


As of 630 AM: Ohio Valley high pressure maintains quiet weather
across the CWFA. Some valley fog and stratus has developed per
satellite fog product and Franklin/Sylva obs. This is expected to
burn off by 9-10 AM, leaving clear skies around the area that will
persist thru the day. Winds will remain NE today, not bringing any
downslope warming that may have been at work yesterday. Thus max
temps in the Piedmont are slightly cooler. However, with full sun
I still favored some component of MOS to warm the blend a bit. The
high builds east tonight which reduces the gradient enough to calm
winds in many areas. Mins accordingly will be a bit cooler. Even
favoring a dewpoint guidance blend on the dry side of the spectrum,
conditions appear favorable for a more widely distributed frost
event across sections of the NC mountain counties, plus the northern
foothills. Given the expected coverage, a Frost Advisory was issued
for tomorrow morning in those areas. Sfc moisture looks sufficient
for a return of valley fog, so this has been added to the fcst also.


As of 135 AM EDT Tuesday: Weak upper trough slides east across the
area through the period. Surface high pressure remains in place
across the area as well. The air mass slowly moderates through the
period as thicknesses slowly rise. Highs slightly below normal
Wednesday rise to right around normal Thursday. Lows Wednesday night
will be 5 to 10 degrees below normal keeping frost potential in play
for the mountain valleys and I-40 corridor. Lows warm to a couple of
degrees below normal Thursday night ending widespread frost chance.


As of 330 AM EDT Tuesday: Guidance has been in good agreement
through Saturday. Now with the 00Z runs, the GFS and ECMWF are in
remarkable agreement through Monday. Upper ridge axis builds over
the area Friday and slides to the coast on Saturday. The center of
high pressure over the area Friday slides off shore Saturday with
some lingering ridging. This means a dry and warm forecast through
Saturday night but with increasing clouds late. Highs will be around
5 degrees above normal with lows starting a little below rising to
right around normal.

A full latitude trough will amplify over the central CONUS on
Sunday, before the southern stream cuts off near the Gulf Coast on
Monday. Although the low cuts off, it doesn`t happen until Monday
and retains some connection with the northern stream until then.
This keeps the low moving instead of stalling well to our west like
previous model runs were showing. At the surface, a moist southerly
flow develops between the departing high pressure and a cold front
moving into the MS Valley. The cold front moves into the area Monday
even as a surface wave forms near the Gulf Coast in response to the
developing upper low. This brings deep moisture into the area along
with good synoptic scale forcing resulting in increasing precip
chances Sunday and Monday. There is even enough instability for some
thunderstorms along and south of the I-85 corridor. Have capped PoP
in the good chance range for now. Highs remain near normal Sunday
falling below normal for Monday. Lows rise to nearly 10 degrees
above normal.


At KCLT and Elsewhere: Dry high pressure north of the region will
maintain clear skies at all TAF sites today. Winds will be mainly
NE. A few low-end gusts are likely in the late morning but these
should mix out quickly. Tonight, the center of the high nears,
and guidance suggests winds will become light and VRB. Despite
temps well below normal within a dry continental airmass, sfc
dewpoint depressions are expected to be fairly small. Some frost
formation is possible in the mountains and foothills, including
at KAVL. Also, similar to what happened this morning, mountain
valley fog/stratus is likely. At KAVL this has prompted mention
of IFR vsby near daybreak.

Outlook: Seasonably cool and overall VFR conditions will persist
through the work week.

Confidence Table...

            10-16Z        16-22Z        22-04Z        04-06Z
KCLT       High 100%     High 100%     High 100%     High 100%
KGSP       High 100%     High 100%     High 100%     High 100%
KAVL       High 100%     High 100%     High 100%     High 100%
KHKY       High 100%     High 100%     High 100%     High 100%
KGMU       High 100%     High 100%     High 100%     High 100%
KAND       High 100%     High 100%     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:


NC...Frost Advisory from 2 AM to 9 AM EDT Wednesday for NCZ033-


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