Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion 
National Weather Service Greenville-Spartanburg SC
326 am EDT Friday Jul 25 2014

Synopsis...
high pressure will build in behind a departing cold front on Friday
lasting through the majority of the weekend. Another cold front is
expected to reach the area from the northwest on Monday morning and
into Monday afternoon potentially leading to scattered
thunderstorms. High pressure will once again regain control on
Tuesday lasting through the remainder of the work week with only
minimal precipitation threats by weeks end.

&&

Near term /through tonight/...
as of 305 am...slow moving cold front keeping enough low level
convergence across the southern upstate to break the cap and produce
isolated rain showers. These should end or move south of the area by daybreak
as the front moves out of the area.

Although the front moves south of the area...guidance is nearly
unanimous keeping low level moisture across the area. In addition...
low level flow becomes southeasterly leading to weak upslope flow. This is
forecast to provide enough lift to tap the elevated instability and
produce isolated to scattered convection along the Blue Ridge and west
across the mountains given the model support...have changed the forecast
to include pop in this area. There may also be some convection
across the far southern County warning forecast area as that area will be close to the front.
However...best chance will be south of the County warning forecast area. Clouds will linger
through the morning across much of the northern and eastern County warning forecast area...before mixing
out by afternoon. This and the cooler air mass behind the front will
lead to highs a little below normal.

Convection should dissipate during the evening with loss of heating.
However...cannot rule out some lingering rain showers over the Blue Ridge
late into the evening or early overnight before the low level flow
becomes southwesterly. Lows should be near normal.

&&

Short term /Saturday through Sunday night/...
as of 230 am EDT Friday...the short term period initializes Saturday
morning with remnant front well to the southeast along the
Carolina/Georgia coastline. Surface high pressure will quickly
build under rising heights aloft. Despite weak Lee trough developing
just east of the forecast area potentially providing a focus for
afternoon convection...soundings indicate a substantial low/middle
level cap in place. Not expecting any potential updrafts to break
through the deep inhibition therefore kept the forecast dry for
Saturday.

Also kept forecast dry through Sunday morning as upper heights are
slow to fall due to approaching upper trough and associated surface
cold front. Still think area of greatest lift and lowest inhibition
will remain tied to Lee trough redevelopment east of the i77 corridor
therefore continue with dry forecast for the Piedmont region through
the afternoon. Further West...Heights will begin to fall rapidly as
upper short wave and associated moisture advect into the
central/southern Apps. Models tend to agree on at least some
precipitation pushing into the northern mountains by middle/late
afternoon on Sunday...with chances increasing ahead of the
approaching front through the overnight. Therefore...solid chance
probability of precipitation are featured Sunday evening along the higher terrain of NC
increasing to near likely probability of precipitation by Monday morning near the Tennessee
border. Elsehwere probability of precipitation taper down sharply to slight chance levels
over the NC/SC foothills and western most areas of the Piedmont.
Temperatures through the short term period will gradually warm as
southerly flow ramps up ahead of approaching surface trough.
Expecting highs on both Saturday and Sunday to surge to above normal
levels with middle 90s possible for southern portions of the forecast
area on Sunday.

&&

Long term /Monday through Thursday/...
as of 315 am EDT Friday...the extended range period will begin with
a rather active pattern on Monday morning. Strong height falls will
be advecting in from the west as a cold front stretches along the
appalachian chain from a parent surface cyclone across the eastern
Great Lakes. Probability of precipitation will initialize at high end chance levels across
the higher terrain as the prefrontal activity pushes into the region
around or just before daybreak Monday. The entire complex will
continue advecting east through the morning and early afternoon
hours allowing for some diurnal destabilization ahead across the
NC/SC Piedmont regions. There is still some uncertainty regarding
overall magnitude of instability that will build ahead of the front
as abundant sky cover will work to limit heating. That
said...modest warm sector already in place will not need much
heating for lapse rates to support substantial low level lift.
Aloft drier air will be advecting in as strong west-northwest flow associated
with trough axis pushes into the region. This will allow middle level
lapse rates to steepen...potentially leading to a fairly unstable
profile. Speaking of...latest GFS forecast soundings indicate
nearly 1500j/kg SBCAPE and long straight hodographs producing deep
layer shear in excess of 35kts suggesting multicell strong/severe
thunderstorms. All that said...there is still plenty of time for the
pattern to change slightly which could substantially alter the
outcome. Thus...due to range in the forecast...kept probability of precipitation capped at
chance levels for the entire region on Monday afternoon.

Surface high pressure will build into the region behind the front
for Tuesday and Wednesday leading to lower precipitation chances
despite persistent upper trough remaining nearly stationary. Forecast
will feature slight chance probability of precipitation across the high terrain through
Wednesday morning amidst strong northwest flow. The surface ridge remains
dominate through the remainder of the period as it repositions
itself to the northeast and extends in a wedge like pattern along
the Lee side of the Appalachians by Thursday. Surface flow will
shift to more of an east to southeast component leading to potential
upslope/upglide precipiation into Friday. Thus chance level probability of precipitation
are once again featured through the remainder of the forecast along
the high terrain with slight chance probability of precipitation highlighted elsewhere.
Temperatures will gradually cool behind the frontal passage on Monday with
highs topping out nearly a category below normal by Thursday for
some locations.

&&

Aviation /08z Friday through Tuesday/...
at kclt...VFR stratocu remains across the area and may lower to MVFR
by daybreak. MVFR fog also may develop before daybreak. Latest
guidance shows any ceiling restriction slowly lifting to low VFR by
noon...with low VFR lingering until late afternoon when it scatters
out. NE wind becomes east-northeast by afternoon and continues into the
evening. That said...there could be some east-southeast wind from late
afternoon into the evening.

Elsewhere...similar conditions to kclt. Kand has less of a chance for
MVFR ceilings...but should still see MVFR visibility near daybreak. Kavl and
khky also have a better chance of IFR visibility and ceilings near daybreak.
Latest guidance shows convection developing from along the Blue
Ridge west across the NC mountains have included a prob30 at kavl. Kavl
will also see southerly wind for the afternoon.

Outlook...Sat through Sunday morning should be quiet and VFR...
except for the mountain valleys where early morning fog may occur. Scattered
thunderstorms may return to the forecast area for Sunday
afternoon...though more likely Monday...as another cold front
approaches and then moves through the area by Monday night.

Confidence table...

07-13z 13-19z 19-01z 01-07z
kclt high 87% high 83% high 96% high 100%
kgsp high 87% high 84% high 97% high 100%
kavl medium 66% medium 77% high 96% high 90%
khky medium 71% medium 77% high 95% high 96%
kgmu high 89% high 85% high 100% high 100%
kand high 89% medium 71% 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: (must be lower case)

Www.Weather.Gov/gsp/aviation_tables

&&

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

&&

$$
Synopsis...cdg
near term...rwh
short term...cdg
long term...cdg
aviation...rwh

National Weather Service Glossary of Abbreviations