FXUS62 KGSP 082357
Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
757 PM EDT Wed Jul 8 2020
A weak area of low pressure will continue to slowly drift along
the North Carolina coast on Thursday. The low will then track
northeast along the East Coast through the rest of the week. Rain
chances will be in store every day of the forecast period with drier
air trying to work into the area by Sunday. Better chances for rain
will be in store for the early part of next week.
.NEAR TERM /THROUGH THURSDAY/...
As of 750 pm EDT: The loss of daytime heating has allowed most
shower and thunderstorm activity to come to an end. These trends
should continue this evening. The forecast is largely on track with
updates focused on aviation interests.
The quasi-tropical circulation along the NC/SC coast this afternoon
will move slowly northward over the Outer Banks tonight through
Thursday. On the western periphery of this system, rich precipitable
water air and weak banding will produce scattered showers and
thunderstorms through mid-evening before the instability wanes.
Meanwhile, differential heating, terrain flow, and weak convergence
will fire ridge scattered to numerous top showers and thunderstorms
over the mountains. Steering flow will take the mountain convection
southwest, with the extreme southern Appalachians seeing the highest
PoPs through late afternoon/early evening. SBCAPE values are already
running around 1500+ J/kg and spotty 2000+ values are likely, which
could lead to a couple of strong to severe storms especially in the
southwest mountains. The convection will wane quickly overnight,
with patchy mountain valley stratus and fog developing.
Thursday could look quite similar to today, but with just slightly
drier air wrapping in on northeast to north flow, and a shallow
ridge stretching along the Appalachians west of the slowly departing
coastal surface low. Expect another round of more numerous ridge top
convection and scattered piedmont activity in the deeper moisture
during peak heating. Maxes will rebound by at least a category.
.SHORT TERM /THURSDAY NIGHT THROUGH SATURDAY/...
As of 130 PM EDT Wednesday: The short term forecast begins Thursday
afternoon with upper troughing still in place over the eastern
CONUS. The upper low that brought unsettled weather to our area over
the past couple days will move off over the Outer Banks, and at this
point it seems likely that some sort of tropical system will result.
The good news is that regardless of development, no direct impact
from this system is expected in our area as it lifts up towards the
northeast. Friday afternoon, an upper shortwave and weak surface
boundary will approach the area from the west, encouraging diurnal
convection especially in the mountains as normal summertime levels
of destabilization occur by the afternoon hours. It seems the front
may hang up before it's able to reach too far into the forecast area
(though with latest model runs this has come into question), so
convection will favor the mountains. As always during the summer, an
isolated severe storm is possible, though nothing about the setup on
Friday looks particularly favorable for numerous instances of severe
weather. Saturday, model guidance has split...there is a decent
chance the frontal boundary will advance through the area before
peak diurnal heating on Saturday and result in very little
convective coverage in the afternoon, but some chance also remains
that the front will be hung up over our area at that point and work
as a focusing mechanism for storms. Either way, chances for severe
weather Saturday look low.
Finally, heat indices may become a concern Friday and Saturday with
a very muggy airmass hanging around the area and heights recovering
enough that max temps increase to a few degrees above climo.
.LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/...
As of 200 PM EDT Wednesday: Model guidance indicates a potential
blocking pattern over the extended forecast period. An immense
upper ridge will set up shop over the southwestern CONUS over the
weekend and promote upper troughing to dig into the eastern third
of the country. A shortwave trough should develop over the Upper
Great Lakes and Ohio Valley by late Sunday into Monday which could
allow for sparse convective development over the region during that
time frame. With the upper trough only gradually pulling away from
the East Coast, drier air should filter in on the backside of the
trough as a persistent northwest flow drives into the area during
the early part of the new work week. Both the ECMWF and GFS are
consistent on the overall large-scale pattern with upper troughing
staying confined to the area through Monday. The latest 12Z run of
the GFS still differs from the ECMWF with the trough deepening and
lifting much slower than the ECWMF starting Tuesday. The ECMWF on
the other hand, extends higher heights into the area by Tuesday
and the middle part of next week. The ECWMF has the upper ridge
in the Southwest stretching to the east and lifts the trough to
the north and east. The timing is inconsistent between the models
this far out, but temperatures should remain slightly above climo
for much of the forecast period with lowering PoPs as we go into
the first half of next week.
.AVIATION /00Z THURSDAY THROUGH MONDAY/...
At KCLT and elsewhere: High confidence in prevailing VFR at most
Piedmont sites except near KCLT where brief MVFR cigs are possible
between 09Z and 16Z and across mountain valleys where IFR cigs/vsbys
are likely sometime between 06Z and 12Z, especially for areas that
saw rain today like KAVL. Isolated (Piedmont) to scattered
(mountains) showers and thunderstorms are expected again Thursday
afternoon into the evening.
Outlook: Afternoon and evening showers and thunderstorms are
expected each day through the weekend. Morning cig/visibility
restrictions will also be possible each day, especially in river
00-06Z 06-12Z 12-18Z 18-00Z
KCLT High 100% High 100% High 96% High 100%
KGSP High 100% High 100% High 100% High 100%
KAVL High 100% Low 35% 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 are available at
the following link:
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