National Weather Service National Headquarters

• Home
• Site Map
• News
• Organization
• Search for: NWS All NOAA 

-- Discussion containing changed information from previous version are highlighted. --
000
FXUS62 KGSP 121054
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
654 AM EDT Wed Aug 12 2020

.SYNOPSIS...
Daily showers and thunderstorms will steadily become more numerous
as the week progresses.  High temperatures of a couple degrees above
normal through Wednesday will become near to below normal by the end
of the week with the deeper moisture and considerable cloud cover.

&&

.NEAR TERM /THROUGH TONIGHT/...
-- Changed Discussion --
As of 630 AM EDT Wednesday: All shower activity died off a couple
of hours ago with a plume of lingering high clouds still evident
on IR satellite. Otherwise, winds remain calm over the majority
of our sites with some mountain valley fog/low stratus currently
being observed at the usual locations. Fog/low stratus should burn
off by 14z or so.

Otherwise, mid to upper heights will recover modestly over the
fcst area today as heights fall to our west over the Mississippi
River Valley ahead of a weak cutoff low. With low-lvl flow expected
to veer back around to SELY across our lower terrain but favor a
more NLY direction over the mtns, this should produce some low-level
convergence and enhanced upslope component. This will likely produce
at least a slight increase in diurnal convective coverage this aftn/
evening across the mountains and adjacent foothills. In addition,
the CAMs have been suggesting that sct convection could linger thru
late tonight and into the overnight as weak low-lvl convergence
persists across the CWFA. As has been the case the past few days,
fcst profiles depict modest lapse rates and seasonably weak shear.
Thus, a few thunderstorms could become severe today/tonight, however
heavy downpours and the potential for isolated flash flooding remains
the primary concern. High temps are expected to top out just above
normal.
-- End Changed Discussion --

&&

.SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/...
As of 320 am Wednesday:  The main driver of the weather across our
area...indeed across much of the Southeast during the late week will
be a upper vorticity center over the western Ohio Valley and
associated frontal zone extending from the lower Miss Valley into
the Mid-Atlantic. As the vorticity center drifts slowly east through
the period, forcing and moisture will increase across much of the
region, with precipitable water values likely reaching...if not
exceeding 2" across much of our area during the Thu/Fri time frame.
Although the better forcing will still be west of the area through
much of Thursday, ingredients should support high coverage of mainly
diurnal showers and storms. The main threat Thu into Thu night...as
it will be for much of at least the next 5 days...will revolve
around the potential for locally excessive rainfall. On Thu, this
threat will be largely driven by the high number of showers/storms,
anticipated warm rain processes/efficient rainfall producers, and
slow cell movement, as forecast soundings depict average LCL-EL mean
wind of < 5 kts.

However, as time goes on, a more organized excessive rainfall threat
could emerge Thu night through Fri night, when guidance is in
generally good agreement in lifting a surface wave west of the
Appalachians, which would tend to focus low level forcing and
relatively strong SE upslope flow into southwest NC. While most
guidance sources reflect this "big picture" scenario, differences in
the intensity and atmospheric response to the key features is
significant among the various solutions, so an organized hydro
threat is by no means a slam dunk, but the signal is there.
Otherwise, high pops...generally 60-80% are carried through the
period. Although the highest pops are tied to the afternoon/evening
peak of the diurnal heating cycle, convection will be possible, if
not likely well beyond this window. Max temps will be near to
slightly below climo and min temps above climo through the
period.

&&

.LONG TERM /SATURDAY THROUGH TUESDAY/...
As of 340 am Wednesday: Very unsettled weather will persist into at
least the early part of the medium range, as the upper vorticity
center of the short term period, which is forecast to be more or
less evolved into a bonafide trough  by the start of the medium
range, will still be to our west, supporting continued tropical
moisture and respectable forcing over the forecast area. This will
support continued high pops...generally 70-80% on Saturday, with a
continued excessive rainfall threat, which is likely to increase
with each day as antecedent conditions steadily deteriorate.
However, as the weekend progresses, the GFS and ECMWF are somewhat
converging toward a consensus in progressing the trough across the
region and shoving the moisture plume east by Monday. Thus, the
forecast will feature a gradual downward trend in pops for Sun-Tue,
also with a trend toward more of a typical diurnal convective cycle.
However, the details of this trend toward less active weather remain
very much up in the air. Temps will begin the period below normal,
but gradually trend back toward climo with time.

&&

.AVIATION /12Z WEDNESDAY THROUGH SUNDAY/...
-- Changed Discussion --
At KCLT and Elsewhere: All shower activity died off a couple of
hours ago with a plume of lingering high clouds still evident
on IR satellite. Winds should be light to calm thru mid-morning
with more of a NELY wind component will set up later this morning
and a SELY direction prevailing for the afternoon/evening.
Otherwise, I anticipate VFR cumulus bases from sfc heating today,
with another round of sct to numerous TSRA this afternoon/evening,
possibly lingering into the overnight. This was handled with PROB30s
at each site, except for KCLT, where the slightly higher PoPs
warranted a TEMPO for TSRA from 19 to 23z.

Outlook: Above normal coverage of diurnal convection is expected
thru the upcoming weekend. Morning fog/low stratus restrictions
will be possible each morning, especially over the usual mountain
valleys.

Confidence Table...

            11-17Z        17-23Z        23-05Z        05-06Z
KCLT       High 100%     High 100%     High 100%     High  90%
KGSP       High 100%     High 100%     High 100%     High 100%
KAVL       Med   65%     High 100%     High 100%     Med   65%
KHKY       High 100%     High  95%     High 100%     High 100%
KGMU       High 100%     High 100%     High 100%     High 100%
KAND       High  90%     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:

www.weather.gov/gsp/aviation
-- End Changed Discussion --

&&

.GSP WATCHES/WARNINGS/ADVISORIES...
GA...None.
NC...None.
SC...None.

&&

$$
SYNOPSIS...DEO
NEAR TERM...JPT
SHORT TERM...JDL
LONG TERM...JDL
AVIATION...JPT