Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 280659

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
259 AM EDT Wed Jun 28 2017

Dry and cool high pressure will continue today, but will move off
the East Coast on Thursday. Warm and moist air will move north from
the Gulf through the weekend, bringing back the summer heat as well
as a daily chance of afternoon and evening showers and
thunderstorms through the Independence Day holiday.


As of 255 AM Wednesday: little change from the last near-term
update with calm conditions prevailing across the fcst area.
Under clear skies and good radiational cooling conditions, the
sfc-based inversion should persist well into the morning. Some
patchy morning fog is possible over the usual mtn valleys and
even the northern NC Foothills, however most locations are too
dry to support visby restrictions this morning. Otherwise, heights
will continue to gradually rise over the region as the upper trof
lifts farther to our NE today and tonight and broad upper ridging
begins to build to our south. At the sfc, high pressure currently
centered just to our north will slowly slide eastward thru the
day and then move offshore later tonight and early tomorrow.
This will cause low-lvl winds to veer around to SELY later today
and then more SLY by early tomorrow bringing a more typical moist,
summertime airmass to the region. As for the sensible wx, continued
low RH thru a deep layer will keep mostly clear skies over the CWFA
with just a few fair wx cumulus breaking out during the afternoon.
SLY flow and abundant sunshine will allow temps to top out about
2 to 4 degrees warmer today than yesterday.


As of 230 AM EDT Wednesday: The surface high will be off the NC/VA
coasts as we begin the short term. A weakness aloft over the Lower
MS Valley combined with the return moisture flow from the Gulf
around the western periphery of the high will allow precip to being
to lift north into the Deep South as isentropic upglide increases
during the day. Best rain chances will generally be across the Upper
Savannah Valley, closer to the deep moisture associated with the
upper weakness, but with widespread cloud cover continuing the trend
of below-normal high temps.

Meanwhile a northern stream shortwave will cross the Great Lakes on
thursday, dragging a weak front through the Upper Midwest and toward
the Ohio Valley Thursday night. As the surface high moves farther
out into the Atlantic, another, deeper wave will dive out of Canada,
with these systems beginning to phase. Temperatures will increase
only incrementally Friday afternoon due to continued cloud cover,
but we`ll really feel the additional surface moisture in the form of
increased overnight lows, which will return back to seasonal normals
by Friday morning and a couple of degrees above for Saturday
morning. Convection chances ramp up rapidly on Friday as all this
moisture pushes into the area, but with moderate instability
(limited by less surface heating than usual on a summer afternoon)
and no shear, expected pulse thunderstorms with slightly better
coverage than usual especially across the western half of the area.


As of 245 AM EDT Wednesday: The wave moving across the northern tier
will phase with the Lower MS Valley weakness around the start of the
period, merging into a longwave trough which puts us in diffluent SW
flow aloft. Attendant cold front will be stretched down the Ohio
Valley and we will remain solidly in the warm sector, with continued
enhancement to diurnal convection expected on Saturday. As for
severe potential, still no real shear to speak of even on Saturday
with the front nearby, but sbCAPEs increase to >2000J/kg by peak
heating Saturday across the Piedmont, so that plus increased PWs
(water loading) may lead to a slightly higher threat for damaging
winds, but not markedly so.

The front is now progged by global models to pass through the area
Saturday night, but don`t let that fool you - between NW downsloping
surface flow off the mountains plus a bit of clearing out of cloud
cover, temperatures on Sunday will rise back to seasonal normals
across the area, and though dewpoints will decrease behind the
front, not enough to wipe out any pop chances. So in this case,
Sunday actually looks like a fairly typical summer day with diurnal
pops...just with NW surface winds instead of S/SW.

The front will slowly meander offshore Monday and Independence Day,
and by this time strongly mixed boundary layer should bring
dewpoints down further at least on Monday, somewhat limiting typical
diurnal convection. By the Independence Day holiday, we are looking
at highs 2-3 degrees above seasonal normals (we knew this couldn`t
last forever), but with convection chances increasing again as
another shortwave pushes down the MS Valley.


At KCLT and elsewhere: VFR conditions expected thru taf period.
The latest IR imagery is showing some lingering patchy stratus in
the 6 to 8kft range over NE Georgia and the Upstate. The stratus
will likely persist well into the morning until we get some solar
heating and the near-sfc inversion erodes. Winds will remain
predominately NLY overnight with some sites going light and vrb.
They will gradually veer around to SELY by midday as high pressure
settles east of the region and become more SLY by the end of the
period as the high begins to move offshore. Some patchy cumulus
will likely pop up during the afternoon, but coverage will remain

Outlook: Moist, southerly return flow will develop around the
offshore ridge on Thursday. As a result, typical summertime
conditions will return by the end of the work week, with mainly
late afternoon/evening SHRA/TSRA causing possible restrictions
through the weekend.

Confidence Table...

            07-13Z        13-19Z        19-01Z        01-06Z
KCLT       High 100%     High 100%     High 100%     High 100%
KGSP       High 100%     High 100%     High 100%     High 100%
KAVL       High 100%     High 100%     High 100%     High 100%
KHKY       High 100%     High 100%     High 100%     High 100%
KGMU       High 100%     High 100%     High 100%     High 100%
KAND       High 100%     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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