155 
fxus62 kgsp 300639 
afdgsp 


Area forecast discussion 
National Weather Service Greenville-Spartanburg SC 
239 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/... 
a weakness in the upper level flow pattern across the forecast area 
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 /07z Saturday through Wednesday/... 
isolated showers remain about one County east of kclt early this 
morning...but presently show no signs of redeveloping to the west. 
Abundant low level moisture will be the main taf concern through 
daybreak...as few to scattered VFR clouds should allow enough radiation 
for MVFR visibility to form throughout and IFR to LIFR conditions from 
kavl to khky after 09z. Any lower visibility/ceiling should scatter out 12z to 
14z with a light easterly flow persisting through the day. 


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...however...is too low to 
forecast presently...but an abundant cumulonimbus field should develop and 
winds will need to be monitored closely this afternoon through early 
evening as any thunderstorms and rain could present a microburst threat. 


Outlook...morning MVFR fog will be likely each of the next several 
mornings...especially at kavl. 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