Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Greenville-Spartanburg SC
1049 PM EDT Monday Sep 1 2014
southerly flow induced by a persistent Bermuda high will continue to
promote diurnal showers and thunderstorms through much of the week.
A frontal passage will occur on Tuesday evening into Wednesday
morning with another front passing through over the weekend leading
to enhanced shower and thunderstorm chances for those periods. High
pressure will once again regain control by early next week behind
the above mentioned front resulting in cooler temperatures
and more settled weather.
Near term /through Tuesday/...
as of 1030 PM EDT...mainly lingering thin debris clouds are expected
overnight across the forecast area. However...another round of
morning low clouds and fog is anticipated in the mountain valleys
given that the airmass has changed little from previous mornings.
Mild min temperatures some 5 to 10 degrees above climatology are featured in line
Meanwhile...the upper ridge across the southeast will be flattened further
by the passage of shortwave along the Ohio Valley through Tuesday. The
numerical models are a bit more robust with convective precipitation
coverage arriving from the northwest with another shortwave during peak
heating late in the day...especially across northwest NC. Improved surface
based instability throughout will then allow scattered activity to
run southeast into the Piedmont on the strength of outflows Tuesday afternoon
and evening. Maxes should reach a bit higher than in previous
days...but with heat index values still remaining around 100 or less
in the warmest southeast sections.
Short term /Tuesday night through Thursday/...
as of 2 PM Monday...short range models indicate that a
weakening middle level short wave will ripple over the region Tuesday
night. The combination of the passage of middle level disturbance and
lingering weak instability should support isolated to scattered rain showers/thunderstorms and rain into
Wednesday morning. Low temperatures are forecast to range from the
middle 60s within the mountain valleys to the low 70s east of the mountains on
Wednesday...middle level heights are forecast to slow rise across the
region...sourced from a ridge centered over the deep south. Models
indicate that remnant vorticity may linger across the western
Carolinas through the daylight hours Wednesday. Forecast sounding
show weak to moderate cape developing by middle afternoon...with little
to no low level shear. The environment should favor scattered to num convection
across the ridges during the afternoon and evening...with scattered
convection east. A blend of favored MOS supports highs from the middle
80s within the mountain valleys to low 90s east of I-85.
On Thursday...surface high pressure will become centered across the Middle
Atlantic States...resulting in weak southeast low level flow. 500 mb heights
across the forecast area will likely rise above 590 dm. Forecast
soundings indicate a weak subsidence inversion developing during the
afternoon around h6. Afternoon convective available potential energy will likely range from from
1500-2000 j/kg across the region. Cin values may erode during the
heat of the afternoon. The NAM limits convection to the high terrain
as the GFS appears much wetter across the foothills and Piedmont. I
will take a compromise of both solutions...forecasting 40 to 50 probability of precipitation
across the mountains to 30 to 40 probability of precipitation across the foothills and Piedmont.
I will forecast high temperatures 2 to 3 degrees above normal...but
slightly cooler than Wednesday due to greater coverage of convection.
Long term /Thursday night through Monday/...
as of 230 PM EDT Monday...an upper ridge will weaken over the region
Thursday night into Sat as the center of 500 mb high retrogrades toward the
western Continental U.S. While a northern stream upper trough digs into the
Great Lakes region. The trough is expected to progress eastward to
the Middle Atlantic States through sun and off the eastern Seaboard by
At the surface...a Bermuda high pressure will remain in place through
Friday night resulting in persistent moist S/southeast flow and slightly above
normal temperatures. Despite the upper ridging...moist profile and moderate
diurnal buoyancy should overcome the weakly capped aloft leading to
low end to solid chance probability of precipitation for diurnally driven convection. Sat
and sun...models have come into better agreement with the timing of
the frontal passage late Sat into early sun. The main concern during this
period will be heavy rainfall due to the combination of slow passage
of the front...moist profile and good buoyancy. Both the GFS and
European model (ecmwf) depict healthy quantitative precipitation forecast response over the mountains Sat and over much of
the County Warning Area on sun. Therefore...have updated probability of precipitation to increase to around
30-50 on Sat and 40-60 on sun. Monday...drier and cooler conditions
expected as the front stays south of the area and a wedge of surface
high builds in from the NE. Temperatures will remain slightly above
normal Thursday into sun and cools down by 5-10 degrees by Monday.
Aviation /03z Tuesday through Saturday/...
at kclt...mainly high debris clouds will persist but thin through
the night with the chances of any lower restrictions toward daybreak
quite limited given the latest soundings and MOS forecasts. A
scattered cumulus field will build through the day on Tuesday with
heating as winds increase from the SW...but speeds will remain less
than 10 knots throughout. Shortwaves moving into western NC from the northwest
late day could allow thunderstorms and rain to make a run toward the Piedmont
again...and prob30 for thunderstorms and rain after 21z appears warranted.
Elsewhere...expect mainly high level debris clouds
overnight...except for another round of low clouds and restrictions
at kavl and across the rest of the mountain valleys. Will go ahead and
feature LIFR conditions with this package given the MOS consensus
and observations this morning. Brief MVFR fog will be possible at
khky...and perhaps kand but only very briefly there. Expect cumulus
to build with heating and winds to remain SW through Tuesday...except at
kavl where northwest flow is expected. Prob30 for thunderstorms and rain appears warranted at
all locations late day...but with the best chances from kavl to khky
Outlook...generally VFR conditions are expected through the rest of
the week...but restrictions are likely early each morning in the
mountain valleys due to low clouds and fog. Diurnally driven
rain showers/thunderstorms and rain are expected each afternoon and early evening...with the
most coverage over the mountains.
02-08z 08-14z 14-20z 20-02z
kclt high 100% high 100% high 100% high 100%
kgsp high 100% high 100% high 100% high 100%
kavl high 95% high 87% high 100% high 100%
khky high 100% high 95% high 100% high 100%
kgmu high 100% high 100% high 100% high 100%
kand high 100% high 100% 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)