Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 160558

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
158 AM EDT Wed Aug 16 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 145 AM EDT: There is a great deal of uncertainty over the
potential for fog across the region this morning. The soil and the
boundary layer remain moist in many locations. The NAM has low
condensation pressure deficits around daybreak, while the GFS/RAP
are much more limited with any fog problems. IR imagery also shows
mostly thin mid and high clouds transiting the region, but
temperatures are already very close to the dewpoints. All told, some
fog is likely, but will keep the mention patchy for now.

Otherwise, the southeastern ridge will become resurgent today
through tonight. Under the slowly building ridge, lapse rates and
afternoon sbCAPE values remain relatively modest and the
convection-allowing models show limited coverage this afternoon and
early evening. Still feel that the best scattered coverage should be
along the east slopes of the Blue Ridge, and western foothill
sections immediately downstream, during the mid to late afternoon
hours. Max temps this afternoon should reach the 90s in most areas
east of the mountains, and heat index values should reach 100 in the
lower piedmont. Expect another warm and muggy night tonight with min
temps some 5 to 10 degrees above climo and another round of patchy
fog toward daybreak Thursday.


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 increasing.

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: Early morning fog remains the primary question
mark as the ground and boundary layer are moist in most locations,
but with some passing mid and high clouds, and disparate model
solutions of daybreak fog. Will feature brief MVFR fog at most
locations, with IFR most likely in the mountain valleys around KAVL.
Will also hint at few to scattered low stratus, but the potential
appears to be quite a bit less than recent mornings. Expect mainly
scattered cumulus with heating today, and PROB30 mainly at KAVL and
across the foothills from KGMU to KGSP to KHKY late this afternoon.
Light winds should toggle south to southwest through the day.

Outlook: The transition to a more typical late summer pattern is
expected by the end of the week, continuing into early next week,
with 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...

            06-12Z        12-18Z        18-24Z        00-06Z
KCLT       High  97%     High  94%     High 100%     High 100%
KGSP       High  89%     High  94%     High 100%     High 100%
KAVL       Low   53%     High  93%     High 100%     High  89%
KHKY       High  89%     High  94%     High 100%     High 100%
KGMU       High  97%     High  94%     High 100%     High 100%
KAND       High  97%     High  94%     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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