Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 211751

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
1251 PM EST Tue Nov 21 2017

Moist southerly flow in the lower atmosphere will bring some small
chances for rain or drizzle until a weak cold front crosses our area
tonight.  A passing area of low pressure to our south may bring some
precipitation to the Midlands and Southern Upstate on Thanksgiving
Day. However, from Friday through early next week, dry high pressure
will dominate our weather.


As of 1000 AM EST: Isentropic upglide continues across the area, but
moisture hasn`t descended quite as low as expected, so have pulled
back on pops and bumped up high temperatures slightly. No changes to
overall sky cover even though cloud bases aren`t quite as low.

Otherwise, upglide-induced stratocumulus has moved across most of
the area this morning. Coverage will continue to increase through
the day. The numerical models continue to indicate that isentropic
lift and shallow moisture mainly below 850 mb will move north across
the area this morning. The guidance also says precip should have
already developed in this flow. However, radar remains clear and no
surface obs are showing any precip. This is fortunate as there are a
couple of locations with temps below freezing, although trends show
warming with the low clouds moving in. Have slowed the precip onset
again as a result. Have slight chc PoP spreading across the entire
CWFA during the day as moisture and lift increase. Have chance PoP
along the NC/SC/GA border where upslope flow is maximized. The
moisture is very shallow, so even with the increasing lift, QPF
response is very light. Highs will be a few degrees below normal.

The isentropic lift moves east tonight taking the better precip
chances with it as a weak cold front moves through from the NW. Even
with the front moving through, low level moisture lingers across the
area keeping clouds in for much of the night. Skies may clear soon
enough for areas of fog to develop before daybreak. Lows will be
around 5 degrees above normal.


As of 300 AM Mon: Confluent flow over the Eastern Seaboard on
Wednesday will allow dry and cool high pressure to expand in from
the west. Under a light downsloping flow and abundant sunshine,
max temps will rise a couple degrees above normal. Meanwhile,
during the day a shortwave will move over the central to eastern
Gulf of Mexico and initiate cyclogenesis. Wednesday night these
features will approach the Florida Peninsula, and moisture advection
will occur ahead of them up into GA and SC. While most model runs
of late have indicated this moisture would not extend far enough
inland to affect our CWFA, the 21/00z GFS broke from the trend of
the previous couple of runs, and shows some QPF early Thursday over
the southeastern zones. The GFS does suggest enough warm advection
occurs to keep temps comfortably above freezing; the drier guidance
is colder. I did nod to the GFS by blending some of its influence
into the fcst--both in moisture and temperature. Thus the small
portion of the CWFA that gets a precip mention gets it as all
rain. Mins actually end up about normal.

The coastal low advects over to the Atlantic later on Thursday,
and low-level temp advection basically becomes neutral as the high
re-exerts its influence. However, with a colder start and a cool
northeasterly flow, maxes will be quite a bit cooler, mainly in the
lower to mid 50s. Though thicknesses begin to rebound Thu night,
settled conditions and decent radiation will keep mins slightly
below normal.


As of 200 AM Tue: Rather good agreement noted among the consulted
models for the medium range period. The pattern effectively amplifies
over the CONUS this weekend, as one shortwave over the Midwest phases
with a second one rolling off the ridge over the Intermountain West.
This will bring an initial cold front into the area Saturday,
followed by the slow expansion of Canadian high pressure into the
area from the west. Moisture is a bit lacking to expect any NW Flow
snowfall to develop at this point. Nonetheless by Monday morning we
may experience the coldest temps of the season yet, remaining quite
cold into Tuesday morning even as heights begin to rise overhead.

Temps will trend warmer Friday to Saturday, with maxes a little above
normal Saturday afternoon. The front then will knock maxes/mins down
considerably, with blended guidance bottoming out as much as 10
degrees below normal Sunday night and Monday.


At KCLT and Elsewhere: VFR through the evening, with the
exception being KAVL where some MVFR cigs may continue off and on.
Moisture will return tonight and expect MVFR cigs and vsbys to move
in overnight. Confidence moderate on this, with some guidance
hinting at IFR, but the trend has been improving, and soundings not
indicative of much in the way of restrictions. In any case, expect
rapid improving after sunrise. Winds will be lgt/vrb overnight, with
KCLT trending SE early but all sites swinging to the N by this
evening. Winds will pick up tomorrow between 5-10kt.

Outlook: Dry/cool conditions will continue through late week.

Confidence Table...

            17-23Z        23-05Z        05-11Z        11-12Z
KCLT       High  87%     High 100%     High 100%     High 100%
KGSP       High 100%     High 100%     High 100%     High 100%
KAVL       High  94%     High 100%     High 100%     High 100%
KHKY       High 100%     High 100%     High 100%     Low   58%
KGMU       High 100%     High 100%     High 100%     High 100%
KAND       High  94%     High 100%     High 100%     High  83%

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:




SHORT TERM...Wimberley
LONG TERM...Wimberley
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