Scientific Forecaster Discussion

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Area forecast discussion 
National Weather Service Greenville-Spartanburg SC
706 am EDT Sat Apr 19 2014

Synopsis...
a moist low pressure system will move slowly across southern Georgia
today...and continue tracking east off the South Carolina coast
tonight through Sunday. High pressure will briefly build in
Monday...before a cold front pushes across the region on Tuesday. A
broad and dry area of high pressure will then build in from the
north Wednesday and linger through the end of the week.

&&

Near term /through tonight/...
as of 700 am EDT...water vapor imagery continues to show a tongue of
middle and upper level dry air wrapping into the SW half of the
forecast area this morning. Precipitation has largely transitioned
to drizzle in these areas...and probability of precipitation have been pared back from the
SW with areas of drizzle added to the forecast. Otherwise...the
increasingly stacked southeast low pressure system will continue drifting eastward
toward the coast. Still anticipate a brief resurgence in forcing 12z
to 18z as deep layer qg forcing crosses the region and an axis of
frontogenesis persists across The Heart of the forecast area through
early afternoon before weakening late today into tonight. The greatest
quantitative precipitation forecast should impact the Charlotte metropolitan area...but given the weak
rainfall rates observed thus far...as well as the ffg and headwater
guidance values...it appears that any Hydro problems will be quite
isolated.

In addition...the tightening pressure gradient will cause NE winds to
pick up...with gusts well into the 20s and possibly above 30 miles per hour at
times this afternoon across the Piedmont. Surface cad remaining in place
through tonight will keep the diurnal temperature range fairly small.
Precipitation should gradually end from the west tonight as the
moisture and forcing diminish.

&&

Short term /Sunday through Monday night/...
as of 230 am Saturday...the stacked low pressure system will continue to
slowly drift east away from the Carolina coasts on Sunday...with
wrap-around cloud cover and decent northeasterly low level flow lingering atop the
County warning forecast area. It does look like probability of precipitation should pretty much be over across the area
by daybreak Sunday...but a slight chance does linger in the southeast zones through
midday. With the cool NE flow and lingering clouds...I undercut MOS
temperatures...especially in the east.

Sunday night through Monday...shortwave ridging ripples across the area
behind the departing low. Temperatures rebound to near normal readings
under mostly clear skies.

Monday night...the next shortwave trough approaches from the west.
Height falls aloft and low level moisture arriving within increasing westerly
flow may support a few showers along the NC/Tennessee border overnight. But
otherwise...just an increase in clouds and temperatures a couple categories
above normal.

&&

Long term /Tuesday through Friday/...
as of 245 am Saturday...models still in good agreement on timing a
cold frontal passage across the County warning forecast area on Tuesday. The front will be relatively
weakly forced. But there should be enough q-vector convergence coupled
with low level frontal convergence and moisture to support at least
scattered showers with the front. The timing looks good for about
maximum daytime heating instability...with the GFS most bullish with up
to 1000 j/kg of SBCAPE by 18z Tuesday. However...I think the
downslope west/northwest low level flow will limit coverage and overall instability. The
GFS hodographs also Don/T show much shear for organized
convection...with unidirectional west/northwest flow only increasing to about
30 kts in the middle levels. Temperatures will be above normal...upper 70s to lower
80s east of the mountains...assuming front pushes through late aftn/eve.

Tuesday night through end of the week...upper flow continues to be quite
progressive...with another upper ridge building in for Wednesday and
Thursday...followed by another latitudinal trough approaching the area
Friday. Temperatures remain near or slightly above normal...with the surface
high pressure center translating east across the Great Lakes. A cold front
will push into the Ohio Valley Friday...with slight chance to low-end chance
probability of precipitation creeping back in by Friday evening.

&&

Aviation /11z Saturday through Wednesday/...
at kclt...deformation zone precipitation over or near the airfield
will likely keep IFR ceilings in place through 15z...with mainly MVFR
ceilings continuing through the day. The tightening pressure gradient should
easily produce gusts into the 20s through most of the taf period.
Slow improvement to VFR is possible tonight as the deformation zone
moves east and weakens and the moisture becomes shallower.

At kavl and khky...precipitation rates in and near the deformation
zone should be light enough to allow ceilings to stay mainly VFR tempo
MVFR through the day...with improvement to more solid VFR tonight.
Brief north to NE wind gusts are likely as well...but with less
magnitude than taf locations farther southeast.

At the upstate taf sites...a middle and upper level dry slot has worked
in over the SC tafs. This has lessened the precipitation to drizzle
or very light rain...and allowed ceilings to dip into the IFR range at
times. Mainly IFR is expected through late morning...with MVFR ceilings
the rest of the day...improving to VFR tonight. NE flow will
steadily increase as the pressure gradient tightens...and gusts to 25 knots
will be likely today through this evening.

Outlook...ceiling restrictions may well linger into Sunday morning
before moisture pulls away with the slowly departing offshore low
pressure system. Dry high pressure will then develop through
Monday...with a fairly wet frontal system expected on Tuesday.

Confidence table...

11-17z 17-23z 23-05z 05-11z
kclt high 84% high 85% high 82% high 94%
kgsp high 91% high 87% high 89% high 93%
kavl high 85% high 81% high 98% high 100%
khky high 89% high 84% high 100% high 100%
kgmu high 91% high 86% high 89% high 93%
kand high 95% high 92% high 86% high 86%

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: (must be lower case)

Www.Weather.Gov/gsp/aviation_tables

&&

Gsp watches/warnings/advisories...
Georgia...none.
NC...none.
SC...none.

&&

$$
Synopsis...Arkansas
near term...hg
short term...Arkansas
long term...Arkansas
aviation...hg