Area Forecast Discussion
Issued by NWS Greer, SC

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000
FXUS62 KGSP 021126
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
626 AM EST Fri Dec 2 2016

.SYNOPSIS...
Dry and cool conditions will persist through Saturday. Increased
moisture will return from the west on Sunday and linger into early
next week. Another cold front will approach the area later next week.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 630 AM EST...Only minor changes needed with this update. I
freshened the hourly T/Td grids with latest obs, and updated the sky
grids with latest guidance to show gradual increase in cirrus this
afternoon thru tonight.

As of 230 AM EST...a relatively quiet day for the region, as surface
high pressure continues to slowly build into the area from the
west today under quasi-zonal flow aloft. Skies are expected to be
sunny with relatively light winds, except for some lingering gusty
winds in the NC mountains. Highs will be similar to yesterday,
perhaps a degree or two cooler (near normal).

Tonight, the axis of surface high pressure will settle over the
area, with the center still over the Ohio Valley. A deep trough will
begin to close off over northwestern Mexico, with a moist low
pressure system developing in association with it over Texas. Some
increasing cirrus is expected to spread across the area within a
flat upper ridge, but shouldn`t have too much effect on min temps.
Temps are expected to fall into the 20s to upper 30s across the CWFA
(which is around normal).

&&

.SHORT TERM /SATURDAY THROUGH MONDAY NIGHT/...
As of 230 AM EST Friday: We begin the short term dry with confluent
westerly flow aloft as a strong upper low remains parked over NW
Mexico and the SW US, with downstream ridging increasing in
amplitude over the Plains. Surface cyclogenesis is progged to begin
but will develop first as an inverted trough generally along the
Gulf Coast as a deep trough dives into the northern and central
Plains from Canada. Moisture will begin to spread northeast toward
the Southern Appalachians on Saturday ahead of the shortwave, with
the operational models in decent agreement and with support from the
ensembles. Temperatures should be pretty close to normal on Saturday
but this may be tempered by timing of increasing clouds.

Surface high pressure will slide east along the Great Lakes, pushed
along by the progressive wavetrain as the upper trough moves toward
the Mississippi Valley (with the closed low still spinning over
Mexico). As axis of the surface high crosses the Appalachians, it
will ridge down the eastern seaboard in a transient damming-like
pattern which will push the bulk of the precipitation to our south,
though some decent totals may still creep into the Upstate and NE
GA. The bigger challenge will be the timing of the cold air from the
high and the incoming moisture early Sunday across the northern
mountains. Bufkit soundings for Boone (KTNB) all show a deep near-
freezing isothermal layer but with partial thicknesses indicating a
freezing rain/rain event. WSW flow aloft may indeed lead to a little
warming aloft but thinking with the strong winds in the split flow
pattern, there will be enough orographic uplift to support wet snow
rather than freezing precip. While we could see some minor
accumulations (grids have between 0.1-0.2") anything that falls
should melt as temps warm (somewhat) during the day and ptype
changes to all rain. But speaking of temps, the cool high pressure
trying to wedge into the area should keep temps a good 5-8 degrees
colder than on Saturday and close to 10 degrees below seasonal
normals.

The moisture fetch from the Gulf and Eastern Pacific remains in
place with the southwest flow aloft over the Gulf Coast as the
initial shortwave damps and moves off the East Coast. The Mexico
upper low begins to fill and slide east toward TX late Sunday into
Monday. Ridging again developing over the Mississippi Valley in
response to yet another shortwave diving into the Rockies will lead
to some confluent flow over the Upper Ohio Valley, with the
corresponding surface high strengthening as the upper ridge
increases in amplitude. This leads to a more pronounced diabatically-
enhanced classical CAD setup with a much stronger ageostrophic
adjustment that should be a little more successful at shunting the
precipitation to our south late Monday. As the TX low continues to
fill and lift northeast, the slug of Gulf moisture will spread
across the southeast with a Miller-B-looking surface pattern, slowly
pushing the wedge front back northeast. Some uncertainty in the
amount of available instability but this will be highly dependent on
timing of CAD erosion so for now no thunder at this point, just
another round of rain. Storm total QPFs through the short term range
from about an inch in northeast zones to not quite 2.5" southwest.

&&

.LONG TERM /TUESDAY THROUGH THURSDAY/...
As of 2 AM EST Friday: the medium range fcst picks up at 12z on
Tuesday with a compact upper lvl shortwave passing just to our NW
as broad upper ridging amplifies over the Eastern CONUS. Ridging
is expected to remain over the region trough Wednesday a broad upper
trof moving pushing the ridge offshore by the end of the period on
Friday. At the sfc, a fairly strong low is expected to lift out of
the NW Gulf of Mexico on Monday and pass just to our west early
Tuesday. The long range models are in good agreement that the system
should be lifting northward and up over the Great Lakes by late Tuesday
with drier air spreading back over the CWFA during this time. The
remainder of the period appears more unclear wrt the sfc pattern.
The 12z ECMWF develops a very deep low over the southern plains and
moves its cold front to our doorstep early Thursday with drying high
pressure in the front`s wake for Friday. The 00z GFS develops a low
just to our north early Thursday and also sweeps a cold front across
the CWFA around that time. The GFS solution is noticeably drier with
the fropa compared to the ECMWF, however both scenarios have a quick
fropa so overall QPF is not that great. As for the sensible fcst, the
highest POPs are during the first 12 hrs of the period with slight to
solid chance POPs beyond that. Temperatures start out around normal and
warm on Wed and then drop to well below climatology by day 7.

&&

.AVIATION /12Z FRIDAY THROUGH TUESDAY/...
At KCLT and Elsewhere: VFR thru the period, with generally just
periods of cirrus streaming by this afternoon thru tonight. The main
concern will be wind direction at KCLT, as a lee trough will likely
back the winds from NW to WNW or WSW. Guidance is mixed on what will
be most predominant. However, most of the time, the winds end up WSW
for most of the afternoon in these situations. So will side with
guidance that has WSW for this afternoon. Winds will also likely go
WSW at the Upstate sites. At KAVL...low-end gustiness out of the
north is expected from midday thru the afternoon. Winds should
weaken and favor a NW to N direction this evening thru tonight.

Outlook: Dry high pressure will persist over the region through
Saturday. Precip and restrictions may return as soon as Sunday as
another cold front moves into the region. Low pressure may develop
along the front to our west and bring a second shot of moisture into
the region Monday night into Tuesday.

Confidence Table...

            11-17Z        17-23Z        23-05Z        05-06Z
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 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:

www.weather.gov/gsp/aviation

&&

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

&&

$$
SYNOPSIS...JPT
NEAR TERM...ARK
SHORT TERM...TDP
LONG TERM...JPT
AVIATION...ARK


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