Area Forecast Discussion
Issued by NWS Greer, SC

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000
FXUS62 KGSP 191432
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
1032 AM EDT Thu Oct 19 2017

.SYNOPSIS...
Cool high pressure will move off the East Coast 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 season.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 1015 AM: Valley and lake fog is burning off, and a patch of
cirrus can be seen exiting to the east. So this should leave the
area with sunny skies from midday thru the aftn. Temps are starting
out a bit cooler than current forecast trends, but should rebound
quickly with full sun and light winds. So max temps look good.

A passing shortwave trough has led to a splitting of the sfc high
that was already in place over the Mid-Atlantic coast. A smaller
closed high thus sits over the NC/VA Piedmont attm. This high will
drift inland thru tomorrow morning, strengthening as heights rise
over the eastern half of the Mississippi Valley. In terms of
sensible wx there will be little change today compared to yesterday.
The airmass continues to modify, meaning max temps today will rise a
bit warmer, topping out 1 or 2 categories above normal per
bias-corrected MOS values, which have been performing well this
week. Mins will be a shade below normal. Moist conditions and
quiescent pattern may allow some fog to develop again tonight,
though confidence is low as to how much. Revised extent is based
partly on persistence and partly on NAMNest vsby output.

&&

.SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/...
As of 145 AM EDT Thursday: Upper ridge builds in from the west
Friday. The axis of the ridge slides to the Atlantic coast Saturday
as a deep trough builds into the central CONUS. At the surface, the
center of high pressure starts the period over the area but slides
off shore on Saturday. A moist southerly flow develops Saturday
night, but the moisture remains too shallow for precip. There will
be increasing clouds however. Highs 5 to 10 degrees above normal
Friday drop a couple of degrees Saturday. Lows near normal Friday
night rise a couple of degrees Saturday night.

&&

.LONG TERM /SUNDAY THROUGH WEDNESDAY/...
As of 350 AM EDT: Guidance agrees that the ridge over the East Coast
moves off shore as a deep trough develops over the central CONUS.
Guidance also agrees that the southern stream of this trough splits
off as an upper low forms near the ARKLATEX region with the upper
stream wave continuing east on Monday. The low is then kicked NE as
another deep wave drops into the trough on Tuesday. The deepening
trough slowly moves east toward the area Wednesday. However, there
are timing and strength differences regarding the upper low.

At the surface, a moist southerly flow develops between the
departing high pressure and approaching cold front associated with
the trough. The GFS is faster moving the front, and an associated
surface wave, into the area Monday and Monday night, then east of
the area Tuesday. The ECMWF is about 12 hours slower. Either way,
expect increasing precip chances, thunderstorms and heavy rainfall.
However, there is still quite a bit of uncertainty given the timing
and eventual evolution of the features meaning it is still too early
to peg a best time frame for any heavy rain or potentially severe
storms. Temps should slowly fall to near normal by Tuesday.

There is good agreement that a cold air mass moves in Wednesday
behind the departing cold front. Guidance has backed off on the
potential for any NW flow snow, but showers will be possible. Highs
fall to 10 to 15 degrees below normal.

&&

.AVIATION /15Z THURSDAY THROUGH MONDAY/...
At KCLT and Elsewhere: Deep dry high pressure will remain over the
region. With the exception of some passing cirrus associated with
a weak shortwave, skies accordingly will be clear. Winds will be
light and VRB for the most part, resulting in short TAFs. Excellent
radiative cooling tonight is expected to bring back valley fog,
even over some rivers/lakes in the Piedmont. Restrictions are not
likely enough to mention at any TAF site.

Outlook: VFR conditions will persist through the end of the 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...

            14-20Z        20-02Z        02-08Z        08-12Z
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  95%

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...RWH
NEAR TERM...ARK/Wimberley
SHORT TERM...RWH
LONG TERM...RWH
AVIATION...Wimberley


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