Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 281048

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
648 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 640 AM Wednesday: the latest IR imagery continues to show patchy
stratus in the 6 to 8kft range streaming across northern Georgia
and the Upstate. The stratus will likely persist for a few more
hours until we get some insolation and the near-sfc inversion
erodes. 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 12z taf period.
The latest IR imagery continues to show patchy stratus in the 6 to
8kft range streaming across northern Georgia and the Upstate. The
stratus will likely persist for a few more hours until we get some
insolation and the near-sfc inversion erodes. Winds will gradually
veer around to SELY by midday as high pressure settles east of the
region and become more SLY by early Thursday as the high begins to
move offshore. Some patchy cumulus will likely develop during the
afternoon, but coverage will remain limited.

Outlook: moist, SLY 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...

            10-16Z        16-22Z        22-04Z        04-06Z
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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