Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 210715

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
315 AM EDT SUN AUG 21 2016

A cold front will push through the area from the northwest this
evening and tonight. High pressure will build in behind the front
Monday,  bringing cooler and drier air to the area for most of the


As of 300 AM EDT Sunday: The near-term forecast will usher in a very
welcome pattern change as we push into the work week! A deep upper
trough working its way across the Great Lakes early this morning,
with corresponding surface low at the southern tip of James Bay will
drag a cold front into and through the Appalachians through the
period. Convection across central TN at AFD time will approach the
NC mountains toward daybreak, though upslope flow across the western
slopes will likely allow some isolated showers to develop and push
over the state line before that. Right entrance region of the upper
jet streak will move across the Southern Appalachians this afternoon
and evening along with an elongated area of DPVA, with a
corresponding blob of just over 30kt 0-6km shear. Surface
instability will be limited by widespread cloud cover but still with
around 1000 J/kg sbCAPE plus some mid-level drying working its way
in, plus the aforementioned deep-layer shear, and we should see more
organization to the storms today than we`ve seen most of the summer.
Low-level lapse rates and that mid-level drying will support
isolated wet microbursts, but mid-level lapse rates not supportive
of much in the way of hail. With that, certainly an isolated severe
storm or two cannot be ruled out with strong winds and heavy rain
being the main threat, but storms should move along at a nice clip
with 40kt westerly winds between 700-500mb through the day.

As the front passes across the mountains, it will break up somewhat
as the upper dynamics continue to lift northeast with the surface
low. Additionally, downslope drying will also affect the integrity
of the front. As it pushes east, convection chances will be lower
across southeastern zones.

Expect highs today a couple of degrees below seasonal normals, but
the real effect of the front will be felt tonight, with overnight
lows expected 4-5 degrees cooler than what we`ll see this morning as
the cooler and especially drier air advects in starting just before
midnight in the mountains and spreading across the area through


As of 300 AM EDT Sunday...An upper ridge will build back in across
the Southeast states for Monday and Tuesday, providing subsidence
and mid-level warming to cap any convective chances. To help keep
things stable, a nice, late summer dry-ish air mass will settle in
across the region from the NW. Surface high pressure will slowly
drift east from the Ohio Valley to the Mid-Atlantic by late Tuesday.
Temps will be near or slightly below normal with noticeably less
humidity than we have seen in a while, as dew points drop into the
50s and  60s.


As of 315 AM EDT Sunday...The 00z cycle of guidance continues to
trend drier for the latter half of the week, as upper ridging holds
on across the eastern CONUS thru the end of the week. The low-level
flow will briefly turn around out of the SE on Wednesday, as high
pressure drifts off the Mid-Atlantic coast. This may result in
enough moisture and shallow instability coming off the Atlantic for
some isolated showers in the afternoon across the SW NC mountains and
adjacent mountains/foothills of NE GA and SC. But overall, Wednesday
looks dry with temps near normal.

Thursday thru Saturday, temps gradually return to slightly above
normal, as the upper ridge dominates. A cold front will approach
from the west, but basically washes out as it tries to push into the
forecast area. The GFS still shows some weak QPF response in the
high terrain each of the three days, but the 00z ECMWF is dry. So
PoPs were knocked down slightly with this forecast package, and may
still be overdone, if the current trends hold.


At KCLT and elsewhere: Main concern overnight is potential for low
stratus, as well as some possibility of MVFR fog. In addition to
typical mountain valley restrictions that will impact KAVL, guidance
is showing a slug of moisture coming across the Upstate and toward
KCLT in a repeat performance of last night. Have included these
restrictions in a combination of prevailing higher and TEMPO lower
and will monitor as adjustments may be necessary. Continued PROB30
TSRA already going for this afternoon as a front approaches from the
west. Generally SW winds through the period with some low-end gusts
possible especially across the Upstate, but with winds swinging
around NW as the front pushes through. Current timing for KCLT is
03z Monday.

Outlook: Much drier air will filter into the area behind the front
Monday, resulting in fair weather through at least mid-week.

Confidence Table...

            07-13Z        13-19Z        19-01Z        01-06Z
KCLT       Med   75%     High  99%     High 100%     High 100%
KGSP       Med   61%     High 100%     High 100%     High 100%
KAVL       Low   56%     High  92%     High 100%     Med   71%
KHKY       Med   78%     High 100%     High 100%     High 100%
KGMU       Med   66%     High 100%     High 100%     High 100%
KAND       Med   78%     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:




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