Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 211940

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
240 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 200 PM EST Tuesday: High pressure over the Atlantic continues
to dominate across our area, but with a deep trough in place down
the MS Valley. A secondary shortwave diving out of the Great Lakes
will phase with the main trough, with the amplitude continuing to
increase through the period. A coastal low is progged to develop off
the FL/SC coasts this evening, bringing moisture into eastern zones,
while moisture, albeit anemic, attendant with the upper trough will
push into the mountains tonight. The trough will fill somewhat on
its southern edge through the period, swinging across the
Appalachians and off the Eastern Seaboard by the end of the period,
leaving a bit of energy across the Lower MS Valley and Gulf. Model
progs of isentropic upglide are more impressive than the amount of
moisture seen out there right now (on satellite and radar), and bufr
soundings continue to indicate that the moist layer is fairly thin.

Expect lows tonight above seasonal normals as continued plentiful
cloud cover and very little change to dewpoints prevent the
temperature from dropping. With moisture skirting our eastern SC/NC
zones from the coastal low, pops increase to low chances across
those areas. Some slight chance pops continue across the mountains,
with the northern mountains most likely to get some light showers.
Moisture moves out by around daybreak Wednesday, with high pressure
over the Plains beginning to work this way. Gradient will increase
slightly during the day, with N winds picking up around 10mph, with
some low-end gusts (especially upstream of the valleys with the gap
winds) not out of the question. The downsloping component will allow
temperatures to increase a few more degrees tomorrow than today
across the Piedmont, though the CAA behind the upper trough will
cool the mountains down a few degrees. Overall though a very
pleasant day tomorrow.


As of 230 PM Tuesday: A split 500 mb trough will phase into a deeper
longwave over the Appalachians on Thanksgiving, allowing a cool and
dry high pressure to settle in from the NW. As the trough phases,
weak cyclogenesis is expected over the eastern Gulf. The low will
slowly cross the FL Peninsula Thursday thru Friday. The 12z GFS is
still the only model that throws a shallow layer of moisture up into
the southern edge of the CWFA. It keeps a small area of light QPF
just south of Greenwood/Abbeville counties, and even then, the
forecast soundings look too dry for measurable rain. So I will go
with a dry fcst for Thanksgiving. There may be some stratocu across
NE GA and the Upstate, at least thru the morning, but otherwise, it
should be mostly sunny. Temps will be about 10 degrees below normal
on Thanksgiving, then rebound to about 3-5 degrees below normal on


As of 100 PM EST Tue: The medium range fcst period kicks off on
Friday night amidst broad eastern CONUS troffing with a northern
stream wave digging across the upper Midwest, while ridging prevails
out west.  At the surface, the wave that we have been watching
evolve in the guidance for a few days now continues to track
offshore, and therefore yielding no sig impacts across northeast
GA and the western Carolinas.  Weakening high pressure across the
region will allow for a brief period of wly/swly backed surface
flow into/through Saturday before the aforementioned northern
stream wave and surface cold front move into the region in the
evening/overnight hours.  There remains some discontinuity with
regard to any frontal precip as the GFS favors enough upper support
tied to the wave to produce a quick burst of rain, possibly snow
at the highest elevations, while the ECMWF remains dry.  As such,
both of these guidance sources favor no residual nwfs behind the
front among the cold advection.  Therefore, will leave the fcst
dry through this time frame.  Moving along, caa will prevail on
Sunday as deep layer high pressure settles across much of the
southern Appalachians leading to dry conditions and below normal
temperatures into Tuesday.    At that point, the upper ridge begins
to shift east taking the surface component along with it, leading to
sly veered flow and thus waa.  This is all ahead of a late period
front moving across the Mississippi River valley into Wednesday,
which shouldn`t yield any affects on the cwfa through periods end.


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:




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