Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 211140
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
640 AM EST Tue Nov 21 2017

.SYNOPSIS...
Moist southerly flow in the lower atmosphere will bring some small
chances for rain or drizzle today. 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.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 640 AM EST: 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.

&&

.SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/...
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.

&&

.LONG TERM /FRIDAY THROUGH MONDAY/...
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.

&&

.AVIATION /12Z TUESDAY THROUGH SATURDAY/...
At KCLT and Elsewhere: Low VFR cigs will continue through much of
the day with TEMPO MVFR cigs this morning. Guidance has backed off
on restrictions and precip for the morning, so TAF`s are generally
more optimistic than earlier expected. Clouds lower back to MVFR
this evening and may clear out toward daybreak as a weak cold front
moves through. However, this would increase the potential for fog to
develop. For now, have generally gone with MVFR vsby and cigs, but
did put IFR in in the normally more foggy areas. Winds will be light
NE through the day for all but NC sites where they are light S to
SW. Winds turn light NE this evening then light N to NW overnight.

Outlook: Low-level moisture or foggy conditions may keep
restrictions in the forecast early Wednesday morning. Otherwise,
dry/cool conditions should return 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:

www.weather.gov/gsp/aviation

&&

.GSP WATCHES/WARNINGS/ADVISORIES...
GA...None.
NC...None.
SC...None.

&&

$$
SYNOPSIS...Wimberley
NEAR TERM...RWH
SHORT TERM...Wimberley
LONG TERM...Wimberley
AVIATION...RWH


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