Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 141421

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
1021 AM EDT Mon Aug 14 2017

A stationary front is expected to lift northward into the region
today, possibly washing out on Tuesday while another weak front
approaches from the west. This next front will move into the
region Tuesday night into Wednesday with a brief round of drier
high pressure favored through Thursday. Another cold front will
move into the area on Friday warranting increased chances for
precipitation, with drier high pressure expected in its wake for
Saturday into Sunday.


As of 950 AM EDT: Northeasterly blyr flow aiding in the slowing of
clearing of morning stratus, but nonetheless, clouds will lift and
scatter from south to north, generally late morning into early
afternoon. With the blyr flow veering to SE and aided by continual
impulses within the quasi-zonal flow, morning NC mountain showers
will continually expand this afternoon with additional piedmont
development likely.  12Z soundings show freezing lvls above 15k feet
and pwat values about 130% of normal. Thunderstorms should become
numerous later today with the biggest threat being isolated
excessive rainfall. By the overnight hours, lingering isolated to
scattered mountain showers are then possible with additional weak
upper vort lobe energy passing through. Meanwhile, Tropical System
Gert will pass well east of the eastern seaboard and not impact the
area. Expect another night of very warm minimum temperatures some 5
to 7 degrees above climo.


As of 300 AM EDT Monday:  The short term fcst kicks off on Tuesday
morning amidst quasizonal flow aloft at the base of a
broad/departing H5 trof, while ridging builds westward over the
Plains.  At the surface, TC Gert will be approx 300 miles off the
Carolina coastline, with the fcst track driving the storm northeast
further out to sea.  Otherwise, weak surface ridging will be in
place across the southeast CONUS thanks the Bermuda high, however
with some ambiguity in pressure/wind field thanks to Gert.
Shortwave energy looks to pass through the mean flow aloft on
Tuesday while profiles remain rather moist and unstable ahead across
northeast GA and the Carolinas as a weak cold front approaches out
of the OH/TN valley.  With that, think sct/num showers and
thunderstorms are favored given ample instability and continually
elevated PWATS, therefore pops will be reflective of such.

Moving into Wednesday, the aforementioned front is progged to surge
southward into/across the SC Midlands by sunrise, while at the same
time Gert begins to move so far northward that the southeast becomes
under control of the elongated/migrating Bermuda high once again.
The airmass behind the front will lead to slightly lower PWATS on
Wednesday, however weak return flow could lift the front back along
the I85 corridor, which combined with modest diurnally favored
instability will warrant at least climo pops region wide.  All in
all, think the heavy rainfall threat will have diminished somewhat
on Wednesday, at least on a broader scale.  Temperatures on Tuesday
will be at normal levels, warming a few degrees on Wednesday to
above normal.


As of 315 AM EDT Monday:  The medium range fcst period kicks off on
Thursday morning amidst broad ridging centered over the GOM, however
extending northward into the southern Appalachians, while a
shortwave trof digs across the Great Lakes region.  At the surface
high pressure both over Bermuda and the GOM will dominate the
pattern over the southeast states, while a surface trof/front
extends southward beneath the aforementioned upper trof into the
upper/middle MS River Valley.  Pattern evolution will favor lower
precipitation chances on Thursday given proximity of the deep
ridging and only marginal diurnally favored cape, thus near climo
pops were highlighted.  The aforementioned front does look to move
into/through the TN valley Friday morning possibly arriving in
western NC by early afternoon as the upper ridge retrogrades
westward a bit.  As a result, lightly higher pops were included on
Friday as the front slowly moves into the region.  Guidance favors
poor shear in association with this front, thus overall think
convection on Friday will be rather unorganized.

As for the weekend, the weak frontal boundary looks to push south of
the region for Saturday however yielding only marginal, if any
airmass change.  At that point some discontinuity in the op guidance
becomes ever more evident as the ECMWF is a bit more progressive
with the next wave moving in on Sunday while the first frontal axis
lifts back north into the I85 corridor, thereby keeping pops
elevated on Sunday.  The GFS other hand is about 12 hours slower and
yielding a drier Sunday.  Temperatures through the end of the week
will moderate and remain a few degrees above normal, topping out on
Friday before cooling slightly on Saturday and Sunday.


At KCLT: Showers continue to gradually weaken and dissipate near the
airfield around daybreak this morning. Will thus hold onto only a
VCSH mention through 15Z. Otherwise, expect IFR cigs to develop
quickly around sunrise given the abundant moisture, and these
restrictions will be very slow to lift through MVFR through late
morning and the early afternoon. Will feature TEMPO conditions for
afternoon/evening convection as models agree fairly well that robust
convection should develop off the Blue Ridge later this afternoon.
Winds will be mainly N of E and fairly light through the current
period, but brief southeast flow at times cannot be ruled out at.
Expect another light of MVFR to IFR low stratus.

Elsewhere: Upslope showers developing along the SC mountains this
morning should generally not impact the Upstate TAF sites or KAVL.
IFR to MVFR cigs will be the main aviation concern, being slow to
lift through the higher MVFR range through late morning. Anticipate
mainly lower VFR cigs with showers and thunderstorms redeveloping
from the west this afternoon ahead of an approaching shortwave. KAVL
should see TSRA the earliest, by 19Z, with activity spreading to the
foothills from 20Z through 00Z. Winds will be NE early and become
southeast to southerly later in the day. Another night of low
stratus is expected tonight as the precipitation winds down.

Confidence Table...

            14-20Z        20-02Z        02-08Z        08-12Z
KCLT       High  93%     High 100%     High  98%     Med   67%
KGSP       High  92%     High 100%     High 100%     Med   71%
KAVL       High  87%     High  97%     High  83%     High  84%
KHKY       High  92%     High  98%     High  83%     Med   63%
KGMU       High  93%     High 100%     High 100%     High  88%
KAND       High  88%     High 100%     High 100%     Med   78%

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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