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fxus62 kgsp 231102 

Area forecast discussion
National Weather Service Greenville-Spartanburg SC
702 am EDT sun Apr 23 2017

cool and moist high pressure will remain over the area through
Monday. Meanwhile, a deep and vigorous low pressure system moves
across Georgia to the Carolina coast creating a lengthy period of
moderate to heavy rainfall that persists through Monday. Dry high
pressure returns by Wednesday. Temperatures warm through next
weekend with a small chance of afternoon mountain thunderstorms.


Near term /through tonight/...
as of 700 am edt: showers are blossoming across the cwfa, as
isentropic lift and moisture deepens atop a strengthening wedge. No
significant changes were needed with this update.

As of 330 am edt: an upper closed low will continue to slowly drift
southeast from the mid-south to near Columbus, Georgia by 12z Monday. This slow
drift will place the County warning forecast area within a region of very strong deep-layer
q-vector convergence, especially tonight. At the surface, an area of
low pressure will stall over northern GA, while a backdoor cold
front clears our area to the south keeping a hybrid wedge locked in
across the entire County warning forecast area. Persistent low level upglide atop The Wedge
should bring rounds of showers thru the day. The cams seem to agree
on perhaps a couple "rounds" of categorical pops, one this morning,
then another this evening. Total quantitative precipitation forecast amounts today thru tonight will
range from generally 1.5 to 3", highest across the southeasterly upslope
areas of the Blue Ridge and adjacent foothills. So the Flood Watch
looks good for the NC zones. As for severe potential, it really does
look like The Wedge front will make little progress north as the low
is slow to approach from the west, and ongoing rain keeps it
reinforced. I keep a mention of slight chance to chance for thunder across
the I-85 corridor and south/east, due to potential elevated
convection. There is still a marginal risk in the day one convective
outlook for possible hail and wind, but the cams keep the strongest
convection south and east of the County warning forecast area. Temps will be nearly steady
across most of the area, unless The Wedge front does nudge back into
the southern tier of counties, where temps may bump back up into the
upper 60s to lower 70s. Lows tonight drop slightly into the 40s in
the mountains and lower to mid 50s elsewhere.


Short term /Monday through Tuesday night/...
as of 355 am sunday: the heavy rain potential continues Monday as
our area will still be in the southerly diffluent flow/deformation
zone around the upper low moving east from west central Georgia to the
SC/Georgia coast. Upper divergence follows a similar pattern. Strong low
level easterly flow remains over the area as the low level low
pressure areas follow a similar pattern as well. In fact, the low
level easterly flow is up to 3 Standard deviations above normal.
This will create strong isentropic lift over the cold dome from the
damming that remains in place. The moist air mass remains in place
as well with precipitable water values 1 to 2 South Dakota above normal. The heaviest rain
will likely fall across the NC foothills and Piedmont, but could
shift south into the eastern upstate. An additional 1 to 2 inches of
rain could fall in these areas. Therefore, have added Union County
NC to the Flood Watch to cover the potential. Moderate to heavy rain
could linger Monday evening, but precip tapers off from SW to NE
overnight. Highs will increase a little but remain around 10 degrees
below normal. Lows will be up to 5 degrees above normal.

Precip continues tapering off from SW to NE Tuesday ending during
the afternoon. With precip ending and sunshine gradually returning,
highs will be near normal. Dry forecast continues Tuesday night with
lows around 5 degrees above normal.


Long term /Wednesday through Saturday/...
as of 330 am sunday: short wave ridge over the area Wednesday moves
east as a series of short waves move by to our north and west
Thursday and Friday. A stronger ridge develops over the southeast Continental U.S.
Saturday. Dry remains over the area Wednesday with temps above
normal. Moisture returns ahead of a weak cold front Thursday and
Friday. This will lead to diurnal convection each day favoring the
mountains. Temps remain above normal. Southerly flow around the
ridge surface and aloft will keep some moisture across the mountains
with diurnal convection once again. Temps remain above normal as


Aviation /11z Sunday through Thursday/...
at kclt and elsewhere: as expected, IFR cigs have finally filled in
across all the taf sites (except barely MVFR at kavl), as showers
continue to develop atop a building cold air damming wedge. Guidance
is still on track for a period of heavier rain/greater coverage this
morning, then perhaps a relative lull this afternoon. Then another
round of rain tonight. Still may see some elevated thunder across
the upstate and at kclt late this afternoon thru the evening. For
now, only will mention a prob30 at kclt where chance is greatest for
embedded thunder with the second round of rain. IFR cigs will likely
lower to LIFR across the Piedmont sites tonight, as the cold dome of
The Wedge starts to shrink with a passing area of low pressure to
the south. Showers will start to taper off in the west toward the
end of the taf period.

Outlook: an area of low pressure will cross the southern County warning forecast area thru
Monday while strong sfc ridging builds in from the north. Widespread
low clouds and precipitation are expected to persist thru this time.
Conditions should gradually improve Tuesday thru Wednesday morning
as dry air works in behind the departing low.

Confidence table...

11-17z 17-23z 23-05z 05-06z
kclt high 100% low 50% Med 78% Med 60%
kgsp high 87% low 50% Med 78% high 87%
kavl high 87% Med 78% Med 78% high 87%
khky high 81% high 83% high 83% Med 69%
kgmu high 81% low 44% Med 78% high 87%
kand high 87% Med 61% high 100% high 87%

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:



Gsp watches/warnings/advisories...
NC...Flood Watch through Monday evening for ncz033-035>037-048>053-



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