Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 181511

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
1111 AM EDT Tue Jul 18 2017

A stalled frontal boundary will slowly dissipate over the next
few days as a strong upper ridge gradually builds into the region.
This will bring hot temperatures and a reduction in the coverage
of diurnal showers and thunderstorms.


As of 1100 am EDT: Morning low clouds have generally moved east of
the area or dissipated, and heating should consequently get
temperatures quickly back on track toward the lower 90s east of the
mountains. Convective cumulus is already developing over the
mountain ridges and coverage should be fairly solid as a weak upper
vorticity lobe crosses the higher terrain and triggering occurs
first near the Blue Ridge. Decent DCAPE values above 1000 J/kg along
with 25 to 30 K theta e lapses should provide severe gust potential
with any 55 dbz cores above 24 kft. Light northwesterly steering
flow aloft will permit at least scattered coverage east of the
mountains, with a continued heavy rain threat under the best cores.

Otherwise, the upper trough just east of the area will push further
east, likely closing off in a weak cyclonic circulation. An extended
period of steadily rising heights is beginning. Afternoon convection
should diminish fairly quickly after early evening. Temps are
expected to run right around normal through the period, albeit a
degree or two warmer than on Monday.


As of 310 AM EDT Tuesday: the short-term fcst picks up at 12z on
Wednesday with weak upper trofing over the East Coast and very broad
upper ridging in place over the rest of the CONUS. The latest model
guidance now has the upper trof linger over the coast thru Thursday
before becoming separated from the mean flow and spinning off a
weak H5 low early Friday to end the period. At the sfc, broad high
pressure will be centered well to our north with the Bermuda High
in place offshore. The overall synoptic pattern is not expected to
change much thru the short-term period with weak high pressure
persisting to our north and relatively steep low-lvl lapse rates
remaining over the fcst area each day. I kept the near climo PoPs
for Wednesday with Thursday expected to be drier as we`ll likely
see more of a downslope component across the CWFA. Temps will start
out just above normal and warm another 2 to 4 degrees on Thursday
as thicknesses increase.


As of 225 AM EDT Tuesday: the extended fcst picks up at 12z on
Friday with very broad upper ridging over most of the CONUS and
what`s left of a weak H5 low that tries to spin off from the upper
trof that was lingering over the Atlantic Coast the previous day.
The long range models now have the weak H5 low separating from
the main flow as it drifts SW and along the northern Gulf Coast
on Fri and Sat. At the same time, the ridge flattens as upper
trofing amplifies over Eastern Canada. By early next week, heights
will start to lower again as the upper trof digs farther southward
and the ridge amplifies again to our west. At the sfc, the Bermuda
High will be in place to our east keeping light SLY flow over the
region thru most of the period. The models also keep some degree
of weak lee trofing over the fcst area on Fri and into the weekend,
although the GFS is less bullish on the lee trof persisting beyond
Fri compared to the ECMWF. The ECMWF also develops a fairly strong
low over the Great Lakes on Sunday and moves its associated cold
front thru the CWFA on Monday, while the GFS is considerably weaker
with the low and the front appears to stall out just to our NW. As
for the sensible fcst, we can expect diurnally-driven climo PoPs
for Fri and Sat with higher PoPs for Sunday and Monday as the front
could impact the CWFA. Temps will be a good 6 to 8 degrees above
climatology with highs approaching 100 degrees on Fri and Sat and
heat index values approaching advisory criteria.


At KCLT and elsewhere: All morning restrictions have lifted or
scattered late this morning and VFR conditions are expected going
forward. Winds will remain light at 5 kts or less through the
period, likely favoring a southerly direction by afternoon.
Scattered convection is expected to develop this afternoon, first
along the Blue Ridge and later over the foothills/piedmont, although
coverage is anticipated to be just a bit less than in previous days.
Nevertheless, TEMPO TSRA is warranted at at the NC sites with mainly
VCTS or PROB30 across the Upstate. Conditions should be less
favorable for restrictions tonight, with the exception of the usual
mtn valley fog/low stratus developing toward daybreak.

Outlook: Isolated to scattered afternoon and evening thunderstorms
are expected Wednesday across the area, with better coverage over
the mountains. Morning fog development can be expected in the
mountain valleys and in areas that receive rainfall the previous
afternoon/evening. Drier air will likely limit convective coverage
for Thursday, with typical mid-summer conditions returning by

Confidence Table...

            15-21Z        21-03Z        03-09Z        09-12Z
KCLT       High  90%     High 100%     High 100%     High  83%
KGSP       High 100%     High 100%     High 100%     High  89%
KAVL       High 100%     High 100%     High  89%     High  95%
KHKY       High 100%     High 100%     High 100%     High  88%
KGMU       High 100%     High 100%     High 100%     High 100%
KAND       High  98%     High 100%     High 100%     High  83%

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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