Area Forecast Discussion
Issued by NWS Greer, SC
FXUS62 KGSP 210240
Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
1040 PM EDT SAT AUG 20 2016
Warm and humid conditions will continue into Sunday as subtropical
high pressure lingers over the area. A cold front will cross the
region from the northwest later in the day bringing cooler and drier
air to the area for most of next week.
.NEAR TERM /THROUGH SUNDAY/...
As of 1030 PM, a somewhat organized band of moderate to heavy rain
showers is moving across the western third or so of the forecast
area late this evening. The latest runs of the HRRR and the HRRRx
have picked up on this activity, and generally indicate it will fade
into the ether before it reaches the I-77 corridor. That being the
case, will feature likely pops west and solid chances east into the
early morning hours. Locally heavy rainfall is a sure bet within the
band, but the relatively fast movement and absence of any extreme
rainfall rates (< 1 in/hr) should preclude any hydro concerns. Min
temps will average about a category above climo. Areas of fog and/or
low stratus will develop after midnight, especially across the
western half of the area as the current rainfall wets the ground and
saturates the near-surface air mass.
A relatively deep short wave trough moves into the area late Sunday.
The best energy remains to the north, but weak Q-vector convergence
does cross the area during the day. The associated surface cold
front drops into the area during the afternoon as well. This will
lead to increased forcing which should provide better lift than
indicated by the relatively weak instability forecast. Therefore,
expect showers and thunderstorms to increase in coverage and move
across the area from west to east through the day. Despite the
increased forcing and shear, the weak instability and deep moisture
will keep the chance of severe storms low. Heavy rain will be a
possibility, but storm movement will be relatively quick. Highs will
be near normal.
.SHORT TERM /SUNDAY NIGHT THROUGH TUESDAY/...
As of 230 PM EDT Saturday: The short term fcst period kicks
off Sunday evening amidst a passing H5 trof axis, while its
associated surface cold front moves across northeast GA and the
western Carolinas. Guidance favors continued convection into the
late evening hours and the front clears the I85 corridor where any
remnant instability will reside. Beyond that, expecting coverage
to diminish through the nighttime hours leading into a beautiful
start for the new work week. The departing H5 trof will give way to
building heights as a ridge approaches from the west. Likewise at
the surface, cooler/drier Canadian high pressure will advect atop
the OH/TN valleys, extended across the southern Appalachians.
With the old cold front stalled along the Gulf coast, dewpoints
in the 50s/60s, as well as deep layer subsidence, the fcst will
remain dry through Monday into Tuesday. Meanwhile, the parent
surface ridge will move eastward atop New England leading to
the development of a weak wedge in the lee of the Appalachians.
As such, southerly llv flow could combine with moisture along the
periphery of the wedge to induced a few showers/thunderstorms on
Tuesday across portions of the Upper Savannah river valley as well
as the southwest NC and northeast GA high terrain. Therefore pops
will elevate to only slight chance levels for these locales,
remaining below mentionable levels over the remainder of the fcst
area. Below normal temperatures combined with the above mentioned
dewpoints will make conditions fairly comfortable into midweek.
.LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/...
As of 220 PM EDT Saturday: the medium range fcst picks up at 00Z on
Wednesday with upper ridging spreading across the eastern CONUS and
a closed upper low moving eastward across the US/Canada border.
As we move into Thurs and Fri the ridge will likely flatten to a
degree, however it appears to restrengthen as we move into the weekend.
At the sfc, high pressure will be centered to our northeast bringing
slightly cooler temps and drier air to the Carolinas. As we move towards
the end of the work week, he high will slide offshore and a relatively
dry cold front will approach from the NW. The latest model guidance has
been trending drier with this front with most of the deeper moisture
relegated to the north. Behind the front, another round of high pressure
is expected beyond day 7. With a drier front anticipated late in the period,
POPs were lowered a bit from the previous fcst with the best chances still
over the higher terrain. Temps will slowly warm thru the period with highs
starting out below climatology and ending up above climatology by day 7.
.AVIATION /03Z SUNDAY THROUGH THURSDAY/...
At KCLT and elsewhere: Scattered showers persist early this evening
across the NC mtns and northeast GA, with coverage diminishing
considerably east of there. The overall trend in this activity
should be toward gradual dissipation, but VCSH is warranted at all
sites except KCLT through about midnight. The best coverage/chances
for a direct hit by a shower will be over the mtns, and a tempo has
been included at KAVL for the first couple of hours of the forecast
period. Otherwise, the main concern will be the potential return of
low stratus and perhaps fog across the area later tonight.
Confidence is once again highest at KAVL, and have advertised
similar timing/conditions (LIFR, developing around midnight) to what
was seen there last night/this morning. Most of the other terminals
have seen little to no rainfall today, thus chances for stratus
there appear to be lower than last night/this morning. Nevertheless,
there`s enough of a potential to include SCT IFR/LIFR clouds during
the early morning hours. Otherwise, convection will redevelop Sunday
afternoon ahead of a cold front, and PROB30s are included at all
terminals. Light S/SW winds are expected overnight, but these will
increase to 10-15 kts at most terminals ahead of the front Sunday
Outlook: Much drier air will filter into the area behind the front
Monday, resulting in fair weather through at least mid-week.
02-08Z 08-14Z 14-20Z 20-00Z
KCLT High 100% High 98% High 100% High 100%
KGSP High 100% High 100% High 100% High 100%
KAVL Med 76% Low 43% High 91% High 100%
KHKY High 95% High 95% 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 and ensemble forecasts
are available at the following link: