Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 182330

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
730 PM EDT Wed Oct 18 2017

Cool high pressure will move off the East Coast by the end of the
week providing a light south to southwest flow of milder air.
Temperatures will warm a little to a few degrees above normal
through the weekend. A strong cold front will arrive next week
bringing precipitation and potentially the coldest air so far this


As of 730 PM EDT Wednesday: Only real updates to the grids this
evening are for aviation-related parameters, and even then the going
forecast looks pretty good. Made minor adjustments for trends but
temperature trends are beginning to catch up this evening.
Otherwise, little change in the overall synoptic setup for the next
30+ hours. A dry short wave trough will cross the area overnight,
and may bring a few cirrus. Otherwise, dry high pressure will shift
slightly SW to roughly over Boone, NC by daybreak Thursday. We
should see good radiational cooling again tonight. But the air mass
is beginning to moderate, and min temps are looking to be at least a
deg or two warmer than last night across CWA. Given the patchy
nature of frost this morning, I think we should be okay with no
advisory for tonight. I will continue to mention some patchy frost
in the HWO, as the coldest spots may see some. Fog will likely
develop again across the mountain valleys and area lakes, due to the
cool temps, and may become dense in spots around daybreak.

On Thursday, the sfc high continues to drift west as an upper ridge
builds over the lower MS Valley. A slow warming trend should
continue with another very quite and pleasant day on tap. Highs back
in the 70s for everyone below 3500 ft.


As of 2:15pm EDT Wednesday:  Fairly quiet weather in store for
Friday and Saturday as mid-level CONUS ridge builds in from the west
Thursday night along with a surface high.  High pressure gradually
moves east Friday and Saturday, but by Saturday evening, next
upstream frontal system will still be well west of the area.
Surface high will keep winds light and northeasterly and will keep
moisture out of the area.  Thursday and Friday will thus be clear of
clouds and precipitation (except for a few wisps of cirrus) with
temperatures warming.  Highs on Friday will again be pushing into
the upper 70s to low 80s in piedmont areas with highs to the mid 70s
in the mountains.  That will be about 10 degrees above normal.  With
dry air, lows Thursday and Friday morning will still reach
seasonally normal levels, however.


As of 205 PM EDT: Anomalously strong upper ridge will be in the
process of progressing off the East Coast and weakening at the start
of the medium range, as the first in a series of strong short wave
troughs emerge from central North America, with this trend expected
to continue through at least the first half of the medium range.
These features are expected to carve out a very deep trough across
the eastern Conus by Days 6/7.

While the period will begin with a continuation of the warm and dry
conditions seen during the short term, deep (and increasingly moist)
southerly flow developing across the area may bring precipitation
chances as early as Sunday night, as guidance depicts increasing
isentropic lift over weakening/retreating surface ridge. Precip
chances then gradually ramp up through Monday into Monday night,
with likely pops apparently warranted.  If precip does fall across
the area during this time, the initially dry surface air may result
in establishment of in situ cold air damming. Global model guidance
also depicts warm sector instability developing Monday afternoon,
along with increasing shear parameters. Thus, organized/potentially
severe storms cannot be ruled out, and this potential could
gradually expand into Monday night/early Tue depending upon how any
surface boundaries evolve.

A consensus of global model guidance depicts the cold front sweeping
across the forecast area on Tuesday, bringing a much cooler and
drier air mass into the western Carolinas and northeast GA for the
end of the medium range. Post-frontal NW flow could result in shower
chances continuing across the mountains through at least early Wed.
Snow showers will be possible, at least in the higher elevations,
although the mention of snow has been tempered for the time being.
Otherwise, temps are forecast to be as much as 10 degrees below
climo by the middle of next week.


At KCLT and Elsewhere: Cool and dry high pressure in place will keep
conditions VFR for the most part through the period with just some
FEW passing high clouds, but typical mountain valley fog is expected
again. Guidance beginning to back off on impacts to KAVL/KHKY but
kept restrictions in at these sites. Lgt/vrb winds but generally
favoring the N/NE side.

Outlook: Seasonably cool and overall VFR conditions will persist
through the work week with the only possible exceptions being
mtn valley fog/stratus restrictions in the morning. Moisture will
begin to return to the area Saturday in advance of a cold front
early next week.

Confidence Table...

            23-05Z        05-11Z        11-17Z        17-18Z
KCLT       High 100%     High 100%     High 100%     High 100%
KGSP       High 100%     High 100%     High 100%     High 100%
KAVL       High 100%     High 100%     Low   21%     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:




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