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Area Forecast Discussion

439
FXUS62 KGSP 270155
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
955 PM EDT SUN JUN 26 2016

.SYNOPSIS...
High pressure will weaken over the region and shift east before a
cold front sweeps in Monday night. This front will become stationary
early Tuesday leading to enhanced precipitation chances. High
pressure should build in from the north for the middle part of next
week leading to a brief period of drying.  Diurnal precipitation
chances will resume through late week.

&&

.NEAR TERM /THROUGH MONDAY/...
0200 UTC Update: Pops and QPF were adjusted in the NC mountains
based on radar trends. Winds were updated with a blend of the latest
NAM and ADJMAV. Only minor adjustments were made to temperatures.

At 235 PM EDT...satellite imagery shows a cu field across the fcst
area that has developed in the easterly low level flow. A lack of
clouds over the eastern Piedmont is indicative of the lack of
instability over the middle part of NC. Still expect to see some
deep convection over the mtns thru the afternoon, aided by the weak
easterly upslope, and in fact the KGSP radar has detected some
development over the Balsams. A small chance of precip will also be
kept down across the Savannah River basin where the gradient in sfc
CAPE remains.

Over the next 24 hours, we should see a change in the upper pattern
across the Srn Appalachians/western Carolinas. A positively-tilted
upper ridge overhead this evening will gradually break down/
retrograde thru Monday as an upper trof digs over the Gt
Lakes/Midwest. The balance of the overnight hours should be
relatively quiet once any convection that forms late in the day
weakens diurnally. Will hold onto a small precip chance over the
western mountains where a weak return flow of moisture will persist.
The main concern for Monday will be the extent and strength of
convection that may develop after sufficient boundary layer heating.
The new model guidance indicates that a short wave will probably
remain to our NW by the end of the day, along with a pre-frontal sfc
trof that probably will not reach the mtns until late afternoon. As
a result, the best environment for deep convection and strong
thunderstorms will remain to our N and W through late in the day.
Cannot rule out some stronger storms moving into the mtns from
northeast TN, particularly if some organization happens late in the
day over the Cumberland Plateau, however confidence is no better
than it has been in the last few days, so it will not be mentioned
in the HWO. Confidence is only average in the coverage of precip
Monday afternoon as well. Have kept the likely precip probability
mainly because of the guidance and neighbors, but this borders on
ignoring the forecast tenet that suggests leaning toward drier model
solutions when in a drought. The last precip event was underwhelming
and the thought is that the new scenario is more likely to be drier
rather than wetter than fcst. Expect only scattered coverage at best
south/east of I-85 in the afternoon. High temps will be close to
normal.

&&

.SHORT TERM /MONDAY NIGHT THROUGH WEDNESDAY/...
As of 200 PM Sunday: The departure of the prefrontal trough continues
to be depicted at varying speeds by the various models, but the
consensus is that it will move thru the area rather slowly Mon night
and Tue. It likely will continue to provide enough lift to permit
some weak/elevated convection Monday night. The surface cold front
will remain over the lower Ohio Valley, and NAM/GFS depict weak waves
at 500mb (possibly MCVs) moving ahead of the front overnight,
possibly also enhancing lift. Chance to likely PoPs are maintained
thru early Tue. Appreciable drying and downsloping winds do not kick
in until later Tue, so some diurnal destabilization is expected, with
PoPs to match. Max temps will be held down a category or two below
normal by lingering cloud cover.

The cold front pushes into TN and wrn VA by Wed morning, but it runs
out of steam before crossing the mountains into our CWFA. With the
trough axis just to our east and with dewpoints returning to the
upper 50s and lower 60s, convection is expected to be more isolated
and mainly confined to the Piedmont. Temps however will warm back to
around normal.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/...
As of 150 PM EDT Sunday...Pretty good confidence is had over the ext
range period. The op models are showing good agreement with the
large scale subtrop high ridged out across the wrn states and a broad
ulvl trof encompassing the ern conus. This pattern will change
little over the period...with gradual height rises across the east
coast and continued nebulus deep layered flow over the region.

At the low levels...an Atl ridge will nose into the se region and
increase moist flux to some degree. This m/flux is suspect due to
deep convec response seen along an offshore stationary bndry. Yet
there will be enuf existing sfc-based moisture to spawn sct
afternoon upslope -shra/tstms and isol/sct convec elsewhere.
Soundings show low-end instability thru Fri as the mlvls warm...so
dont expect much more than llvl thermally driven pusle-type storms.
On Sat...a weak bndry pushes into the NC mtns as a cP sfc high
builds across the upper Midwest. Meanwhile...the models have been
consistent with developing a eastward propagating wave along this
bndry across the srn plains...which looks to make it to the NC mtns
by late Sat into Sun. There will be better shear along with moderate
CAPE values associated with this feature...so the late weekend
should have better coverage and stronger perhaps more organized
tstms...mainly across the higher terrain and nrn zones. Max and min
temps shud rise slightly each day yet remain arnd normal.

&&

.AVIATION /02Z MONDAY THROUGH FRIDAY/...
At KCLT...VFR. Model time heights suggest low VFR clouds will
prevail, with off and on ceilings. Time heights suggest some lower
clouds around daybreak, but confidence is not great enough to carry
more than scattered clouds at or below 3000 ft. Convective and
precipitation chances will remain off the west late Monday
afternoon. Winds will favor the southeast tonight, and the southwest
on Monday, with gusts mainly limited to daylight hours.

Elsewhere...Guidance shows low VFR clouds prevailing, though cigs
may be off and on per cloud trends. Guidance does show some lower
clouds, but at this time confidence it not great enough to carry
MVFR cigs. Guidance supports MVFR vsby towards dawn at KHKY and
KAND...with IFR at KAVL. Winds will favor the southeast overnight,
and southwest after dawn, with gusts mainly during the day. Mountain
convective chances diminish this evening. Convective chances ramp up
in the morning, continuing into the afternoon.

Outlook: Scattered convection could linger into Tue. Diurnal TSTM
chances will build again on Thursday afternoon. Restrictions should
be confined to thunderstorms, fog in the wake of heavy rainfall, and
river valley stratus each morning.

Confidence Table...

            02-08Z        08-14Z        14-20Z        20-00Z
KCLT       High 100%     High 100%     High 100%     High 100%
KGSP       High 100%     High 100%     High 100%     High 100%
KAVL       High 100%     High 100%     High 100%     High 100%
KHKY       High 100%     Med   79%     High 100%     High 100%
KGMU       High 100%     High 100%     High 100%     High 100%
KAND       High 100%     Med   74%     High 100%     High 100%

The percentage reflects the number of guidance members agreeing
with the schedule TAF issuance flight rule category. Complete hourly
experimental aviation forecast consistency tables and ensemble forecasts
are available at the following link:

www.weather.gov/gsp/aviation

&&

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

&&

$$
SYNOPSIS...SBK
NEAR TERM...JAT/PM
SHORT TERM...Wimberley
LONG TERM...SBK
AVIATION...JAT



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