702 
fxus62 kgsp 301127 
afdgsp 


Area forecast discussion 
National Weather Service Greenville-Spartanburg SC 
727 am EDT Sat Aug 30 2008 


Synopsis... 
a back door cold front will slowly weaken as it moves southeast 
across the forecast area this weekend. Middle Atlantic high pressure 
will then build south over the Carolinas and northeast Georgia 
through the middle of next week. 


&& 


Near term /through tonight/... 
will update forecast to pare back areas of fog mention. Otherwise... 
a weakness in the upper level flow pattern across the forecast area 
will persist today between central Continental U.S. High pressure and offshore 
Atlantic high pressure. The associated vorticity lobe at 500 mb will 
remain in place over the Piedmont of the Carolinas as another 
shortwave sags southeast into the region. Scattered morning 
convection...with associated isolated heavy rain...will continue 
east of the Interstate 77 corridor early this morning. Weak easterly 
low level flow is then indicated near the Blue Ridge this 
afternoon...providing some degree of upslope forcing. Low level 
convergence remains focused over the high terrain circa 21z this 
afternoon. This combination of forcing and instability will warrant 
isolated to scattered thunderstorm coverage across the region this 
afternoon through evening...with the best chances in the eastern Piedmont and 
across the mountains. 


Model soundings continue to feature enough middle level dry air 
combining with boundary layer moisture to produce Delta Theta-E 
values of 25 to 30 k across the region this afternoon. Cape should be 
sufficient for healthy cores to develop and tap this dry air to 
produce a microburst threat. The very light steering flow also 
produces a localized flooding threat with any thunderstorms that 
develop where stream levels are already elevated. Will mention these 
hazards in the severe weather potential statement. 


Given the persistent nature of the upper trough...will learn from 
the past few nights and keep at least isolated probability of precipitation running through 
the overnight hours in the Piedmont. 


&& 


Short term /Sunday through Monday night/... 
as of 220 am EDT Saturday...both the GFS and NAM time a back door cold 
front into the southeast U.S. On Sunday. It appears that the County Warning Area 
will remain south of the cold front for most of the daytime on 
Sunday. Warm thicknesses and 850 mb temperatures should allow temperatures to 
rapidly warm through the early afternoon...with maximum temperatures around 90 
east of the mountains and in the middle 80s within the mountain valleys. Afternoon 
dewpoints may range from the u60s to l70s east of the mountains...likely 
resulting in cape values from 500-1000 j/kg. Given the vicinity of 
the cold front...instability...and low level upslope flow...I will 
forecast schc to chance probability of precipitation during the afternoon for shra/tsra. The 
greatest pop is expected along and east of I-85 from kspa to kjqf. 


By sunrise Monday morning...the back door cold front will likely 
remain within the County Warning Area. NAM and GFS indicate that the front will push 
south across the upstate and northeast Georgia during the afternoon 
and early evening. Model cape values remain limited to 500 j/kg or 
less...possibly supporting a rain showers or thunderstorms and rain. I will indicate schc to 
chance probability of precipitation during the afternoon...especially west of I-26. Maximum 
temperatures are expected to remain 5 degrees cooler than values 
reached on Sunday. 


&& 


Long term /Tuesday through Friday/... 
as of 230 am Saturday...no significant changes were made to the 
medium range forecast. GFS continues to indicate deep ridging across 
the forecast area through the rest of the work week. I will keep the 
extended forecast dry overall with temperatures within a couple of 
degrees of normal values. 0z GFS brings the circulation of Hanna 
along the Atlantic coast during day 6 and 7. This track is a large 
change from the previous run and I will not change the going 
forecast. 


&& 


Aviation /12z Saturday through Wednesday/... 
early morning showers east of kclt have largely dissipated this 
morning and will not need to be carried in the 12z taf cycle. Low 
level moisture persists...but light easterly mixing and few to scattered 
VFR level clouds have largely kept visibility values up all night. Will 
still need to start off kavl with MVFR conditions as Lower Mountain 
valleys should see fog for a couple of hours after sunrise. 


A stationary upper level trough will combine with low level 
convergence this afternoon to produce scattered thunderstorms. 
Confidence of thunderstorms and rain at any taf location remains too low to forecast 
presently...but an abundant cumulonimbus field should develop. Middle level dry 
air in the soundings continues to indicate the potential for gusty 
winds near taf sites with any thunderstorms and rain. MOS indicated MVFR visibility 
throughout for tonight after 06z. 


Outlook...isolated to scattered afternoon thunderstorms will be 
possible again Sunday afternoon...but drying is then expected 
through middle week with predominantly VFR conditions. 


&& 


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


&& 


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