Area Forecast Discussion
Issued by NWS Greer, SC
FXUS62 KGSP 311437
Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
1037 AM EDT WED AUG 31 2016
A weak tropical system will gradually move back off the North Carolina
Coast today. A cold front will approach the region from the north
late tonight with another tropical system emerging from the eastern
Gulf of Mexico on Thursday. This system is expected to remain just
to our south and then east as it moves offshore over the weekend. A
Canadian air mass will build over the region in the wake of the
.NEAR TERM /THROUGH TONIGHT/...
As of 1040 AM, satellite imagery shows cloudiness associated with a
wave of low pressure drifting westward from the coastal plain. Some
of this cloudiness will invade from the east thru the afternoon, but
is not expected to dramatically alter the character of the day. The
clouds will spread west but will also gradually dissipate as they
run into subsidence over the upstate and foothills, so high temps
may not be affected.
A weakness in the subtropical ridge will become more
centered over the forecast area today. This includes the center of a
weak mid/upper-level cyclonic circulation centered near Augusta and
associated surface wave near Savannah. The result for our area will
be slightly cooler mid-level temps and slightly better moisture than
the past couple of days. That being said, forecast soundings remain
rather unimpressive. Sure, most soundings in our area do depict some
positive buoyancy for a change, but it`s weak at best.
Showers and storms are expected to blossom around the surface wave
over the coastal plain later today, and with the mid-level
circulation being displaced quite a bit northwest, some of this
activity will likely make a run toward the Piedmont, as depicted by
some of the mesoscale guidance. (Although the most recent runs of
the HRRR have backed off of this idea quite a bit). All things
considered, can`t see there being more than an isolated shower or
storm outside the mtns, and pops will be held at 20 percent there.
Coverage should be better across the high terrain, where the best
instability is forecast. On the other hand, steering currents are
quite weak, with mean cloud-bearing winds of only 5 kts or so
depicted on forecast soundings. So what cells do develop won`t cover
much real estate. The highest pops (50) will therefore be advertised
across the peaks and ridge tops, with 30-40 percent seeming more
reasonable in the valleys. CAPE and DCAPE will not be very
supportive of strong to severe storms, but the slow cell movement
and slightly-above-climo PWs could result in some localized heavy
Temps will remain above normal through the period. In fact,
virtually identical to the past couple of days.
.SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/...
As of 215 AM Wednesday, Short range models indicate that the axis of
a longwave trough will ripple across the Appalachians on Thursday.
At the sfc, a cold front is timed to sweep across the western
Carolinas and NE GA during the late afternoon to early evening
hours. Further south, NHC forecast indicates that the center of the
system currently known as Tropical Depression Nine will approach the
Big Bend area of FL. Forecast soundings across the CWA indicate that
CAPE values are expected to peak between 1500-2000 J/kg during the
heat of the afternoon. Wind fields are forecast to remain from the
west, with 6km bulk shear in the low 20 kts. Guidance indicates that
mtn convection should develop during the early to mid afternoon.
Deep convection will be carried east over the foothills and Piedmont
during the late afternoon and evening. Given the shear and front
orientation, a line of TSRA will likely develop near the I-85
corridor and then push east across the Lakelands and Piedmont. I
will time 40 to 50 PoPs across the CWA Thursday PM. In addition,
forecast soundings show an inverted V profile across the foothills
and Piedmont, I would anticipate a few damaging straight line wind
events. High temperatures are forecast to range from the low to mid
80s within the mtn valleys to low 90s east.
Thursday night into Friday morning, the passage of the sfc front
will likely slow or become briefly stationary as the tropical
cyclone tracks across northern FL and southern GA. The combination
of the lingering moisture and slow sfc front should support at least
iso convection through most of Thursday night. However, the tropical
cyclone will over over the western Atlantic after sunrise Friday,
tracking briskly to the NE. In the wake of the tropical low, the
cold front should sweep east. Canadian high pressure will gradually
build across the CWA through Friday. High temperatures may range
from the upper 70s within the mtn valleys to low to mid 80s east.
.LONG TERM /SATURDAY THROUGH TUESDAY/...
As of 240 AM Wednesday, the system currently known as TD9 will race
NE off the Atlantic coast Saturday and Sunday. At the mid levels, a
broad trof or closed low is forecast to remain over the western
Carolinas and NE GA before shifting east late Sunday. Conditions
appear to remain dry over the weekend and temperatures warming to
around normal by Sunday.
Monday and Tuesday, dry and mild high pressure centered over New
England will continue to ridge across the southern Appalachian
region. Medium range guidance indicates that a mid level ridge will
gradually develop across the southeast U.S. through Tuesday. It
appears that dry conditions will remain across the CWA through early
next week. High temperatures by Tuesday are forecast to range from
the low 80s within the mtn valleys to upper 80s across the
foothills and Piedmont.
.AVIATION /15Z WEDNESDAY THROUGH SUNDAY/...
At KCLT and elsewhere (except KAVL): VFR conditions are expected
through the period. There will be better chances for showers and
perhaps a thunderstorm developing into the Piedmont (i.e., KCLT and
KAND) from the south, but chances are still only 20 percent, so no
TAF mention attm. Otherwise, light winds are expected to transition
to SE at 4-7 kts by this afternoon, while mainly SCT clouds in the
045-060 range are anticipated late AM/early afternoon.
At KAVL: SCT/BKN LIFR clouds, with possibly some brief MVFR fog will
dissipate by 13Z. Otherwise, light vrbl winds and VFR conditions
through the period. Chances for showers and perhaps a thunderstorm
are higher than the past couple of days, so VCSH is in the forecast
beginning at 19Z, with PROB30s for SHRAs from 21Z into the evening.
Outlook: Convective chances increase in all areas as a cold front
pushes through on Thu, with chances diminishing into Fri. AM
mountain valley fog/low stratus will remain possible through the
week. There is some potential for minor impacts from a tropical
storm (primarily clouds/light shower possibilities) over the weekend,
but it appears more likely that the weekend will be dry/VFR.
14-20Z 20-02Z 02-08Z 08-12Z
KCLT High 100% High 100% High 100% Med 79%
KGSP High 100% High 100% High 100% Med 79%
KAVL High 100% High 100% High 100% High 100%
KHKY High 100% High 100% High 100% Med 70%
KGMU High 100% High 100% High 100% High 87%
KAND High 100% High 100% High 100% Med 74%
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: