Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 150246

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
1046 PM EDT Fri Jul 14 2017

Hot and humid conditions will persist through the weekend, with
scattered to numerous afternoon and evening thunderstorms each day.
A cold front will move into the region from the northwest on
Saturday and stall in or near the area through Sunday. Another cold
front will approach on Monday and move southeast of the area on
Tuesday, with dry and warm conditions arriving by the middle of next


As of 1030 PM EDT: convection looks to be winding down across the
Upstate, as the air mass stabilizes. A few showers and possibly
garden variety tstms will be possible overnight near the TN line as
WSWLY low level flow picks up. Pops were adjusted with the latest
CAM guidance. Temps were also adjusted to line up with obs.

Otherwise, a sharp upper trough is working its way from the Great
Lakes to the Mid-South, with upper ridging over the Southeast and
Carolina coasts. The attendant front is draped down the Ohio Valley,
with lee troughing in place across the western Carolinas, and it
will push through the area tonight and tomorrow.

We should see convection wane overnight, but a good portion of the
hires models are keeping at least some thunder across the area,
enhanced by a boundary moving north across the Deep South. Pretty
much all CAM guidance has convection blossoming across AL/GA and
lifting north/northeast into the SC Upstate after midnight, so have
allowed pops to linger there. Low temperatures should continue to
hover 3-4 degrees above seasonal normals with the moist low-level
airmass in place.

As the front moves through, should see an increase in convection
again on Saturday across the entire area, and the Day2 Marginal Risk
covers just about all but the mountains, with sbCAPEs progged
between 1500-2000 J/kg, limited by increasing cloud cover. Again
mainly a low-end wind threat with steep low-level lapse rates.
However, even with the front moving through, temperatures won`t
really respond, and should rise again to seasonal normal levels on
Saturday with continued low-level WAA.


As of 210 PM Friday: Upper trough over the eastern US strengthens
through the period as a short wave dives into the eastern Great
Lakes Sunday and closes off into an upper low on Monday. A series of
weak short waves will rotate through the trough and across the area
each day. The previous surface boundary across the area washes out
but a lee trough will remain in place. This and differential heating
will provide enough low level convergence and moisture pooling for
convective initiation each day. Moderate instability develops each
day with very high instability possible on Monday as mid level lapse
rates steepen with the arrival of cooler mid level temps. DCAPE
values remain high along with increasing surface delta theta-E
values as mid level dry air returns. Therefore, although coverage
will remain in the scattered range both days, isolated severe storms
with damaging winds are possible. Highs will remain nearly steady a
little below normal while highs remain nearly steady near normal.


As of 200 PM EDT Friday: The medium range beings Monday night amid
another convectively active evening as a surface front pushes
through the forecast area. The extent to which the front will be
able to clear the area on Tuesday is uncertain, and with upper
troughing still in place and an upper shortwave moving through, some
chance for storms will remain despite rising heights. Some drier air
will be allowed to work into the forecast area as an upper high
builds in over the central Plains on Wednesday, with Wednesday now
appearing that it may be a rare pop-free day across our forecast
area. Profiles are still dry on Thursday and the synoptic pattern
won`t have changed much from Wednesday`s configuration, so only
afternoon below-climo pops will enter into the far eastern NC
Piedmont zones where better moisture will be. A weak shortwave will
traverse the area Friday, and despite profiles remaining dry, some
showers may get squeezed out in the higher terrain. Pops remain
below climo everywhere until next Saturday, when another front will
approach the forecast area. Maximum and minimum temperatures will
climb gradually through the medium range before peaking on Thursday
and Friday as an upper high builds in before heights fall
slightly (and temperatures with them) by next weekend.


At KCLT and Elsewhere: Scattered convection continues to develop
along and ahead of outflows that are pushing SE off the Blue Ridge
escarpment. This activity will be near KCLT and the three upstate
sites over the next couple of hours. I will put VCTS and/or TEMPO
for TS for the first two hours of the 00z TAFs. The outflow and
storms will likely result in variable wind gusts. Overnight, the
convection may linger across the SW and Central NC mountains and
possibly out across the Upstate, but coverage should be low. Valley
fog and stratus is expected again at KAVL overnight, quickly lifting
around sunrise. More widespread convection is expected on Saturday,
as a cold front pushes into the area from the north. VCTS and/or
prevailing TSRA will be carried Saturday at all sites.

Outlook: Scattered to numerous afternoon and evening thunderstorms
are expected each day through Monday across the area, with higher
coverage in the mountains. Morning fog development can be expected
in the mountain valleys and in areas that receive rainfall the
previous afternoon.

Confidence Table...

            02-08Z        08-14Z        14-20Z        20-00Z
KCLT       High 100%     High 100%     High 100%     High 100%
KGSP       High 100%     High 100%     High 100%     High 100%
KAVL       High 100%     Low   59%     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:




LONG TERM...Carroll
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