Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 160006

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
806 PM EDT Tue Aug 15 2017

A stationary front is expected to remain across the region through
Tuesday while a second front approaches from the west.  This next
front will move into the region Tuesday night into Wednesday. Drier
high pressure is expected for the end of the week leading to hotter
conditions.  Moist and unsettled weather gradually returns through
the weekend into the start of the new work week.


As of 800 PM EDT Tuesday: Upper trough moving across the Great Lakes
will continue to lift NE through the period, with weak ridging up
the MS Valley ahead of the next (deeper) trough. Gert remains off
the NC coast and shouldn`t bother us. A weak shortwave/channeled
vortmax at the southern end of the Great Lakes trough will continue
to push through our area today as the incoming upper ridge pushes
east and phases with the strong Atlantic ridge. This will slowly
flatten tomorrow but should dominate our sensible weather, leading
to a reduction in afternoon/evening convection.

Speaking of which, only a handful of cells linger across the
forecast area this evening. Will probably still see some isolated
cells pop through the evening, but lower dewpoints and warmer temps
(higher LCLs/LFCs) is expected to preclude the post-sunset
"explosion" in convection that we`ve seen the past couple of

Should see another muggy overnight with some fog/low clouds toward
daybreak, though it should not be nearly as widespread/dense as it
was this morning. As we move into tomorrow and the weak ridge builds
in overhead, temperatures should inch up a couple of degrees, but
any convection should mainly remain limited to the mountains, though
cannot rule out isolated Piedmont convection as well.


As of 130 PM Tue: An upper trough and its surface reflection will be
present over the upper Mississippi Valley late Wed into early Thu,
tracking eastward. The warm front associated with this system will
push out of the Deep South and should be northeast of our area by
Thu morning. A warm mixed layer should remain atop the boundary
layer overnight, possibly resulting in isolated showers where the
WAA generates low-level lift. However all areas will most likely be
dry by the wee hours of the morning. Under a low-amplitude upper
ridge, southwesterly flow will promote diurnal destabilization
Thursday afternoon, characterized by SBCAPE values returning to
the 1500-2000 J/kg range. Based on modest shear and dry vertical
profiles, a seasonable damaging wind threat is a fair expectation,
though locally heavy rain may be of greater concern.

Thursday night heights will fall over the Southeast as that trough
displaces the aforementioned ridge. The sfc low will move along
Lakes Superior and Huron, with the trailing cold front extending
into the Tenn Valley, being oriented immediately west of the
Appalachians by daybreak Friday. While there are differences in the
NAM/GFS/SREF as far as how fast it enters the CWFA, all depict it
doing so between 18z Fri and 00z Sat. The thermodynamics and shear
will be similar to Thursday, but despite the arrival of the front,
modeled convective coverage is slightly less than Thursday. This
may be due to the depicted lower boundary layer RH and slightly
higher LCLs.


As of 215 PM EDT Tuesday:  The medium range forecast begins 12Z
Saturday with a surface front drifting south of the area toward the
Low Country SC and southern GA. Also Saturday morning there will be
an approaching strong shortwave crossing the Mississippi River. For
our area, scattered late day convection across the piedmont and in
the NC mountains with isolated to widely scattered elsewhere. The
axis of the shortwave crosses Sunday and thus we have higher
scattered POPs all across our area also with the stationary front
lingering near the piedmont sections.

The stationary front remains west to east across our region through
Eclipse Day as the front lingers generally between I-85 and I-20.
The ECMWF has the front a bit farther north than the other models
placing it along or just north of I-85. The next trough axis crosses
the Mississippi Valley to start the week with the associated front
reaching our area in mid week. Convection ahead of the front will be

Max temperatures will be around normal Saturday and Sunday then a
little below Monday due to less solar influence with the eclipse.
Max temps on Tuesday near normal with the southerly flow countering
falling heights and considerable cloud cover. Min temperatures about
a category above normal due to the cloud cover.


At CLT and Elsewhere: A much less active evening, convectively
speaking across the terminal forecast area. However, an isolated
cell will linger in the vicinity of KGSP and KGMU for the first 1-2
hours of the period, with a tempo warranted at KGSP through 01Z.
Otherwise, the overnight should be relatively quiet, with more of a
W or NW low level flow (along with lack of significant rainfall)
expected to limit the potential for visby/cig restrictions. However,
restrictions are possible at KCLT, where some rain did fall earlier
this evening, and in the valleys around KAVL, although it doesn`t
look like a slam dunk at either of these sites. At KCLT, opted
to advertise MVFR visby along with SCT IFR clouds after 07Z. Also
stuck with MVFR at KAVL, except a tempo for LIFR was included from
10-12Z. VFR conditions are forecast at the other terminals. Winds
should generally favor a light W/NW direction at most terminals
overnight, veering to N or N/NE on Wednesday. Convective chances for
Wed PM appear to be standard for the time of year, warranting
PROB30s at KAVL/KGMU/KGSP, while coverage should be less near the
other terminals.

Outlook: The transition to a more typical late summer pattern is
expected by the end of the week, continuing into early next week,
with widely scattered afternoon convection and morning low stratus
and patchy fog likely each day, especially in the mountain valleys
and in locations seeing appreciable rainfall.

Confidence Table...

            00-06Z        06-12Z        12-18Z        18-00Z
KCLT       High 100%     High  89%     High  94%     High 100%
KGSP       High 100%     High  97%     High  94%     High 100%
KAVL       High  97%     Med   78%     High  85%     High 100%
KHKY       High 100%     High  97%     High  94%     High 100%
KGMU       High 100%     High 100%     High 100%     High 100%
KAND       High 100%     High  97%     High  94%     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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