Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 142127

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
427 PM EST Tue Nov 14 2017

High pressure will slowly move east over the Atlantic through
Wednesday then a weak front crosses our region early Thursday.
A strong cold front crosses the area over the weekend with much
cooler temperatures to start next week.


As of 415 PM EST: A shortwave trough will exit to our east this
evening, with a shortwave ridge approaching in its wake. At the
sfc, high pres centered over Ohio will drift slowly east toward
southern New England. This will keep a NELY flow over the area.
Forecast soundings show a strong inversion around 825 mb, which
is trapping a stratocu deck across portions of the CWFA. Based
on the cloud trends on satellite, as well as short-term sky
cover guidance, the cloud deck still looks not to completely mix
out before sunset. Touched up sky and temp trends accordingly
with this update. Also there will likely be some cloud
redevelopment overnight as flow remains weak and radiational
cooling helps condense further clouds in the high terrain.
Guidance is not in agreement on this, and the amount of clouds
will obviously have an impact on min temps. For now, trended a
little cloudier near the Escarpment and blended in SREF/ADJMET
temps to bump them up slightly.

Wednesday, the stratocu should clear out, as flow turns out of the
west-northwest and increases enough for better downsloping. A cold
front will be pushing into the Ohio and mid-Mississippi Valley. Some
cirrus may start spreading in from the west during the afternoon.
Otherwise, it should be mostly sunny. Temps will remain below
normal, as thicknesses remain low.


As of 130 PM EST Tuesday: The model guidance continues to show a
progressive upper pattern through the latter half of the week. The
passage of an upper trof axis still appears to be on track for
moving eastward across the fcst area Wednesday night and early
Thursday, but timing has slipped enuf to suggest precip will
not have reached the mtns before 00Z Thursday. The better forcing
still looks like it will miss us to the north and what moves across
our area looks very weak. That combined with the strong westerly
component to the flow and lack of moisture inflow from the Gulf
does not bode well for precip chances east of the mtns. The best
forcing and moisture will be the WNW upslope on Thursday morning,
which still does not look all that impressive because it is expected
to be shallow and short-lived. Thus, have cut back precip chances
more into the slight chance range and further limited them to areas
closer to the TN border. Min temps should be well above freezing
early Thursday morning, so it should fall in liquid form. High
pressure building in from the WNW should clear us out as the ridge
moves eastward on Thursday afternoon. The rest of the period will
be seasonally cool and dry with temps a category below normal as
the surface high moves from the OH Valley to the Carolina coast.


As of 220 PM EST Tuesday: Guidance continues the timing
discrepancies for the weekend frontal system. The short waves
driving the frontal system are less amplified yet slower on the
ECMWF while the GFS is more amplified yet faster. They agree that
the associated cold front crosses the area with at least numerous
shower coverage. However, the GFS is at least 6 hours faster. The
GEFS mean is slower than the GFS but not as slow as the ECMWF.
Therefore, have gone with a model blend but keep a slower trend.
Kept PoP limited to high chance across the mountains and 40 range
elsewhere. Highest PoP CWFA wide is Saturday afternoon, but chance
PoP lingers Saturday evening. There will be some NW flow across the
mountains behind the front, but the amount of CAA differs as the GFS
is quite a bit colder then the ECMWF given its amplification. Still,
cannot rule out some high elevation snow showers, but no significant
accums currently expected. Minimal instability is shown on any
model, so no thunderstorms expected yet. QPF looks to be moderate at
best given the quick movement of the system. Breezy and possibly
windy conditions expected across the mountains behind the front with
low end breezy possible elsewhere. Winds taper off as dry high
pressure builds in Monday and Tuesday. Temperatures will be above
normal ahead of the front then falling below normal behind the front
through Monday. Temps warm Tuesday but remain below normal.


At KCLT and Elsewhere: moisture trapped under a strong inversion is
keeping low vfr to mvfr cigs along and east of Blue Ridge escarpment
into late AFTN. Some of this cloud cover may linger thru tonight,
primarily near the escarpment and adjacent foothills. Flow should pick
a little out of the west ahead of an approaching cold front and
scatter out the low clouds Wednesday. So I have cigs scattering out
for late AFTN into evening, then some return of cigs, especially at
KAVL and KHKY tonight. Winds will favor a NE direction, except SE at
KAVL thru the period.

Outlook: Another front will move into the region from the northwest
Wednesday night into Thursday, but moisture will be limited, so
restrictions are not especially likely. A more robust front is
expected over the weekend.

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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