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Area Forecast Discussion

631
FXUS62 KGSP 301051
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
651 AM EDT THU JUN 30 2016

.SYNOPSIS...
Weak high pressure currently in place over the Mid West will drift
slowly eastward toward the area by the end of the week. A slow
moving cold front will stall out south of the area before slowly
pushing northward and moving north of the area by the beginning of
next week.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 645 AM EDT Thursday:  Tweaked fcst over the next hour or so
to account for patchy dense fog across portions of the SC Upstate as
well as the NC piedmont.  Expecting said fog to erode over the next
hour with no expansion in the meantime, thus no DFA is planned.
Otherwise, current fcst remains on track with no other changes
made at this time.

Previous Discussion:  The upper pattern hasn`t really changed
all that much over the last 24 hours as an anomalous trof prevails
across the east/central CONUS while a large anticyclone rotates over
the Desert Southwest.  At the surface, the pattern has evolved to
feature high pressure centered over the Ohio valley as an old front
remains stalled/draped atop the western Carolinas and northeast GA.

Current conditions are highlighted by sct debris stratus across
much of the NC/SC piedmont consequent of earlier convection which
has now weakened and or migrated east of the region.  Near term
highres guid remains insistent in that patchy fog will develop
along/south of the I85/I77 corridors by morning, which will be
highly dependent on persistence of the above mentioned stratus.
Moving on, the fcst looks pretty much like a repeat of yesterday
as convection is expected to initiate along the Blue Ridge,
propagating into the NC/SC piedmont as well as portions of
Northeast GA.  Nam fcst profiles across the region feature
generally 20-30kts 0-6km shear amidst steep low/mid level lapse
rates yielding upwards of 2.5-3.0k j/kg sbcape, which is probably
a bit overdone.  With that, SPC has placed the entire fcst area
into the marginal risk for severe thunderstorms, thus the HWO will
highlight large hail and damaging winds being the primary threats.
The official fcst will feature isolated showers and thunderstorms
by late morning across the mtns, increasing to sct levels by late
afternoon into the evening hours over the remainder of the area.
Pops will lower toward/after midnight to non mentionable levels by
daybreak Friday as profiles become relatively stable overnight.
Temperatures today will be a bit tricky given this morning`s
stratus, thus opted to lower maxes by around a degree across the
board as llv rh fields are very moist supporting mostly cloudy
skies.  Therefore, highs today will top out a few degrees below
normal with overnight lows at or just above normal.

&&

.SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/...
As of 155 AM EDT Thursday: Upper trough axis moves east of the area
Friday. Zonal flow sets up by Saturday with a weak short wave moving
through the flow north of the area. A weak frontal boundary drops
into the area Friday and stalls over the area for Saturday. Despite
the boundary moving in, the low levels will be much drier on Friday
leading to meager instability. There will be enough instability and
low level forcing for isolated diurnal convection however. Precip
chances increase Saturday as low level moisture surges back in ahead
of a surface wave moving along the front. PoP trends will remain
mainly diurnal on Saturday, but convection could linger through the
night. Temps will remain a few degrees above normal.

&&

.LONG TERM /SUNDAY THROUGH WEDNESDAY/...
As of 305 AM EDT Thursday: Zonal flow remains over the area as a
subtropical ridge builds across FL and into the Gulf of Mexico. Weak
short wave activity crosses the area in the zonal flow Sunday before
a stronger short wave moves into or crosses the area Monday and
Tuesday. The guidance is in some disagreement on the strength of
this short wave and its resultant speed. An additional short wave
drops into the area Wednesday on one model. On the other, the
stronger slowly moving short wave drops into the area. Either way,
it looks like there will be upper forcing and support for lift each
day.

At the surface, the frontal boundary remains across the area on
Sunday then lifts north on Monday. The GFS has a strong surface low
moving between the Great Lakes and OH valley on Tuesday, while the
ECMWF has a faster low moving off shore from that area Tuesday. Both
the ECMWF and GFS stall the trailing front across the area
Wednesday. Given the uncertainty, will go with a guidance blend
which keeps mainly scattered diurnal convection across the area each
day. While it`s still too early to pin down the best period, heavy
rainfall and severe storms may be develop at some point. Temps start
the period near or a little below normal on Sunday rising into the
low to mid 90s by Tuesday and Wednesday.

&&

.AVIATION /12Z THURSDAY THROUGH MONDAY/...
At KCLT and the SC Sites:  A mixture of vfr/mvfr and ifr this
morning as low stratus and patchy fog prevails for the first hour
or so before lifting to low vfr.  Otherwise, convection remains
in the fcst for the afternoon/evening hours with tafs featuring
prob30s with vcsh/vcts through 01-02z before low vfr stratus
dominates through midnight.  Guidance is favoring possible fog
again on Friday morning, especially over the NC piedmont, thus
did include mvfr at KCLT only.

At KAVL/KHKY: Trends similar to that of the sites above with
afternoon convection timing adjusted for site location, with
tafs featuring prob30s at both sites by mid/late afternoon.
Winds will remain light and northerly over the next few hours,
veering southerly by late morning.

Outlook: Diurnally favored shra/tsra through the rest of the week,
with restrictions possible adjacent to said convection, as well
as each morning where moderate/heavy rainfall occurred previously.
Shra/tsra chances increase further Saturday into Sunday as another
cold front drops in from the north.

Confidence Table...

            11-17Z        17-23Z        23-05Z        05-06Z
KCLT       Med   61%     High  95%     Med   66%     Med   66%
KGSP       High  89%     High  90%     High 100%     High 100%
KAVL       High  89%     High  95%     High 100%     Med   71%
KHKY       High  83%     High  95%     High 100%     Med   64%
KGMU       High  89%     High  95%     High 100%     High 100%
KAND       High 100%     High 100%     High  95%     High  93%

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...RWH
NEAR TERM...CDG
SHORT TERM...RWH
LONG TERM...RWH
AVIATION...CDG



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