Area Forecast Discussion
Issued by NWS Greer, SC
FXUS62 KGSP 241326
Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
926 AM EDT WED AUG 24 2016
High pressure will persist over the region through midweek allowing
temperatures to climb back above normal. Another weak cold front will
approach the Western Carolinas from the northwest toward the end of
the work week, with high pressure building back to our north over the
.NEAR TERM /THROUGH TONIGHT/...
900 AM update...Slow-moving rain shield presently sits just north of
I-85 from Greenville area to the GA line. It is moving so slowly and
indistinctly it is hard to tell how it will propagate over the next
few hrs. SPC mesoanalysis suggests that no matter what direction it
moves, it will be moving into more stable air; perhaps this is can
be attributed to the cooling effect of the rain shaft and associated
erosion of low-level inversion. Steering flow is very weak but
should be east or southeast; this is reflected also in latest HRRR
depictions of the activity. RAP profiles indicate worsening lapse
rates aloft and some drying nearer the sfc, so the activity may
not recur once it fizzles out at midday, but we`ll have to see
how temps rebound following the erosion of stratus. Similarly,
over the mountains, the low stratus blanket appears likely to delay
destabilization, so the increase in diurnal PoPs has been slowed.
A large upper 596 dam high at 500 mb will continue to dominate the
Southeast, keeping a subsidence inversion in place atop most of the
CWFA. As the high builds slightly, it will push a plume of higher RH
in from the west. This axis will be across the western third or so
of the CWFA this afternoon. That is the reasoning for the expected
return of mountain convection. The model consensus is for isolated
to scattered showers with a few embedded garden-variety tstms,
as CAPE and shear will be marginal. The 00z NAM was thrown out,
however, due to grid-scale convective feedback over the southern
NC mountains. Steering flow will be out the north, and will
try to carry this activity into the Upper Savannah Valley, which
should be modestly unstable (SBCAPE around 1000 J/kg) assuming
the clouds/precip do dissipate and destabilization can occur. So
will go with consensus chance PoPs in the mountains and the Upper
Savannah Valley. Temps will be similar to yesterday`s readings.
Tonight...Anyway showers and/or storms that do develop should
dissipate quickly with loss of heating this evening. However,
deep-layer moisture will linger atop the CWFA, which will keep skies
partly to mostly cloudy overnight. The 850 mb flow will shift from
SELY to NWLY as the low-level high pres shifts westward slightly. So
instead of stratocu from upslope flow, perhaps more mid and high
cloudiness. Temps will bottom out at or slightly above normal.
.SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/...
As of 315 AM EDT Wednesday...the short term fcst picks up at 12Z
on Thursday with broad upper ridging in place over the SE CONUS
that will persist well into the medium range. At the sfc, high
pressure will move farther NE of our area on Thursday allowing the
wedge to weaken and essentially dissolve. An area of pre-frontal
moisture will pass to our north later on Thursday and into Friday,
yet the model guidance has been trending a bit drier since yesterday
and keeps most of the deeper moisture out of the CWFA. As the front
lifts farther NE late Friday and into Saturday, another high slides
over the Great Lakes in its wake. As for the sensible wx, the models
have been trending a bit drier overall but still have more moisture
over the higher terrain especially on Thursday. Temps start out around
climatology if not just above, and warm thru the period with highs on
Friday and Saturday about a category above normal.
.LONG TERM /SATURDAY THROUGH TUESDAY/...
As of 3 AM EDT Wednesday...the medium range fcst picks up at 12Z
on Saturday with broad upper ridging in place over the SE region.
The ridge is expected to flatten a bit on Sunday and Monday but
still maintain control over the overall synoptic pattern. It is
noteworthy that the 12Z run of the ECMWF continues to develop a
tropical low over the Bahamas early in the period and move the
low due west across Southern Florida and then north over the
northern gulf coast by day 7. The newer 00Z run of the GFS also
tries to develop a low over the same area, but it remains considerably
weaker at this time. At the sfc, high pressure will be centered to
our north over the Great Lakes keeping things mostly dry for the
weekend and early next week. The big question comes just beyond
day 7 and the possibility of a tropical system moving into the
Gulf of Mexico and making landfall along the northern gulf coast.
It is still too early to have much confidence in any specific
model track, but it`s looking like a tropical low will develop
during that timeframe. As for the sensible fcst, no major changes
were necessary with below climo POPs for the period and temps about a
category above normal.
.AVIATION /14Z WEDNESDAY THROUGH SUNDAY/...
At KCLT...Pesky southeasterly upslope flow has produced patchy
MVFR-level stratocu across the piedmont this morning. Forecast
soundings show that mixing heights will be slow to lift the stratus
to VFR levels...perhaps not until around midday. Overall, they
should remain patchy, but guidance hasn`t been handling the low CIGS
well. Later today, more moisture around should support convection
across the mountains and the Upper Savannah Valley. In fact, shallow
showers have already been developing across portions of the Upstate.
I will start the three Upstate sites with VCSH this morning. KAVL
will feature VCTS this afternoon. Tonight, flow will turn more out
of the west or northwest. So it should be a little better fog setup
rather than stratus. However, will keep fog confined to mountain
valleys for now, with an IFR Vsby at KAVL late tonight. Winds will
be light thru the period, generally out of the south or southeast.
Outlook: A deep ridge will remain in place over the Southeast thru
the weekend, keeping afternoon SHRA/TSRA chances below normal each
day, and generally confined to the mountains. However, sfc moisture
will gradually return, and morning vsby restrictions will become
increasingly likely during this time.
13-19Z 19-01Z 01-07Z 07-12Z
KCLT High 100% High 100% High 100% High 100%
KGSP High 80% High 100% High 100% High 100%
KAVL High 86% High 97% High 100% Med 65%
KHKY Med 78% High 100% High 96% High 98%
KGMU High 81% High 100% High 100% High 100%
KAND Med 70% High 100% High 100% High 90%
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: