Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Greenville-Spartanburg SC
1038 am EDT Sat Sep 5 2015
a cool and moist wind flow off the Atlantic this weekend will keep
considerable cloudiness and cooler temperatures over our region.
Expect gradual warming during the early to middle part of the
upcoming week under an upper ridge. A cold front and upper trough
will arrive at the end of the week.
Near term /through tonight/...
as of 1030 am...earlier shower activity has dissipated along the
SC/NC border S of eho. Widespread low clouds had moved in across the
Piedmont of the Carolinas and foothills from the NE. The cloud cover
will result in a slow warmup over these areas...which will delay
and/or inhibit destabilization. Will change the forecast to lower the
pop at least over the western Piedmont of NC through late morning. The
thinking is that eventually enough holes will develop in the clouds to
allow for enough heating to support scattered showers and storms from
early afternoon Onward. The best chance for precipitation will be over the
west where better insolation will allow for more instability and a
cloudy/clear boundary provides some focus for deep convection. The
models more or less seem to key on that feature...with comparatively
more development west and less development east. Temperatures will not be
changed at this time.
Remainder of previous discussion...
A weak upper trough will remain over the area today and tonight while
surface high pressure builds into the area from the NE in a wedge-like
pattern. The resulting east to NE low level flow will keep copious low
level moisture in place across the County warning forecast area. This combined with the
conditionally unstable air mass in place will lead scattered convection
today. Best chance will be across the western County warning forecast area where upslope flow and
better instability exist. The convection will slowly diminish through
the evening with scattered chance lingering along the Blue Ridge and isolated
elsehwere overnight. Although moderate instability develops...dcape
values are forecast to remain below 1000 j/kg...so only isolated severe
storms expected. Could see isolated heavy rainfall...especially if
storms become anchored along ridges in the Ely flow or training
cells develop. Despite the surface high placement...this is not a great
set up for a strong cold air damming event with little isentropic
lift or wwa above The /Wedge/. Do expect cooler highs today due to
clouds and precipitation. Lows tonight will be near to above normal.
Short term /Sunday through Monday night/...
at 230 am EDT Saturday...on Sunday morning an upper low will be pver
the southeast...while ridging extends form Texas to teh southern Great
Lakes to the northeast. The upper low retrogressers southwest to teh
Gulf Coast by Monday...where it remains into teusday night. Week
upper level energy rounding the trough will move west acorss the
southner Appalachians on Sunday before the trough moves SW.
At the surface...high pressure will remains banked up agains the
east slopes of the Appalachians on Sunday and Monday. The models
show modest isentropic upglide from the west over this surface ridge
on Sunday...that diminishes on Monday. Low level flow remains from
the NE...limiting upslope flow into the mountains. Considering these
factors...precipitation is not expected to be excessive.
Temperatures will warm from below normal to near normal.
Long term /Tuesday through Friday/...
at 230 am EDT Saturday...on Tuesday a southern stream upper trough
will be over the Gulf states...between upper ridges over northern
Mexico and the western Atlantic. This pattern persists into
Wednesday. By Thursday the Gulf trough weakens...while a northern
stream trough over the northern plains starts to amplify. The
northern trough amplifies over the MS River Valley on Friday.
At the surface...on Tuesday and Wednesday high pressure centered
over the middle Atlantic region will extend south over the Carolinas
and Georgia. This ridge weakens on Thursday as a cold front approaches
from the northwest. The front decelerates as it reaches our area on Friday.
Model instablity is greatest on Tuesday and Wednesday on the east
side of the upper trough...but appears to be strangely tame ahead of
the approaching front and associated falling heights aloft late in
the week. Precipitation is not expected to be exccessive...as
steerign flow remains sufficient to keep cells moving...but upslope
flow...when present...is rather week. Temperatures will run near
Aviation /15z Saturday through Wednesday/...
at kclt...rain showers moving southeast toward the airfield will bring some visibility
restrictions before MVFR ceilings move in. The MVFR will slowly lift to
low VFR through the morning. Additional convection expected today... so
tempo and prob30 for thunderstorms and rain retained. MVFR clouds move back in
overnight with IFR possible. Northeasterly winds continue through the period.
Become northeasterly and continue through the period.
Elsewhere...similar conditions as kclt. Kavl the exception with calm
winds becoming southerly...then back to calm overnight.
Outlook...a moist easterly flow will continue through Sunday...bringing
a good chance of IFR/MVFR restrictions Sunday morning. Light precipitation
will remain possible. The threat for restrictions will continue through
Sunday night. Dry air working in from the east on Monday will begin to
diminish the threat for early next week.
14-20z 20-02z 02-08z 08-12z
kclt high 81% high 100% high 100% high 83%
kgsp high 100% high 100% high 100% low 58%
kavl high 100% high 100% high 100% high 87%
khky medium 76% high 100% high 100% medium 77%
kgmu high 100% high 100% high 100% low 58%
kand high 100% high 100% high 100% medium 62%
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)