963 
fxus62 kgsp 231500 
afdgsp 


Area forecast discussion 
National Weather Service Greenville-Spartanburg SC 
1000 am EST Monday Nov 23 2009 


Synopsis... 
a cool and moist wedge of high pressure will linger over the region 
into Wednesday. A cold front will cross the area Thursday... 
followed by high pressure late in the week. 


&& 


Near term /through tonight/... 
main forecast challenge for the morning update will be how 
widespread and intense drizzle will be. Also a few breaks in the 
clouds are possible across the central NC mountains otherwise...it will 
be cloudy and cold...with a northeasterly wind east of the mountains 


12z radiosonde observation analyses show that middle levels will continue to dry 
out...while at 850 mb and lower will remain moist. Trends in the 
visible satellite imagery...as well as the metars across the 
moutains...indicates some drying of bl and thinning of cloud cover. 
East of the mountains...guidance seems to be in decent agreement on 
continued lift in the 850-925 mb layer (albeit weak). So enough lift 
to keep areas of drizzle in the forecast (especially the NC 
foothills and piedmont). 


Temperatures were adjusted with the 12z nam12...as the NAM has good handle 
on partial clearing across the mountains...and overall temperatures in the cad. 


Tonight...the 12z NAM disagrees with the 06z GFS on continued 
istentopic lift across the forecast area...and actually is bullish on 
clearing the stratus from west to east overnight. I will not make 
any changes to tonight/S forecast with this update. 


&& 


Short term /Tuesday through Wednesday night/... 
as of 245 am Monday...somewhat of a tricky forecast during the short 
range. Although weaker...cad appears to remain in place on Tuesday with 
surface ridging over the area as coastal low moves north away from the 
area and next frontal system is well to our west. There will not be 
much in the way of precipitation...but lingering patchy drizzle is likely 
during the morning outside of the mountains temperatures will be tricky as well 
as clouds diminish over the west...but hold tight in the east. Have 
blended guidance over the mountains and went toward the cooler NAM 
elsewhere. This gives avl a higher maximum than clt/gsp. A better chance 
of rain Tuesday night as isentropic lift increases ahead of the 
approaching front and another weak surface low moves along the South 
Atlantic coast. Have kept pop at slight chance for now with areas of 
drizzle and fog developing in the continued Ely low level flow. Lows 
remain above normal. 


The cold front moves into the area from the west Wednesday as the surface low 
moves up the coast. Slight chance pop continues during the day with the 
continued isentropic lift. Precipitation chance tapers off over the mountains 
during the afternoon as the moisture moves east. The damming regime 
finally abates...but have trended toward the cooler guidance with 
light rain and cloudy skies. This puts highs right at normal levels. 
The precipitation ends Wednesday night as moisture and lift move east of the 
area...but clouds remain. Lows fall to a few degrees above normal. 


&& 


Long term /Thursday through Sunday/... 
as of 230 am EST Monday...both the European model (ecmwf) and GFS show a closed upper 
low over Illinois on Thursday morning. On Friday this low reaches Ohio...an 
on Saturday the tip of Long Island. By Sunday an upper ridge extends 
from the Tennessee Valley to Michigan. The European model (ecmwf) was preferred by HPC for 
details...as its solution has been more consistent. 


On Thursday a pair of cold fronts will move across the southern 
Appalachians...one early in the day...reinforced by the second late 
in the dat. The first front will clear the Lee of the mountains of 
low level moisture...while the second front will introduce a cold 
and moist upslope flow to the mountains on Thursday night. Snow 
levels will fall to the valley floors Thursday night. With such a 
strong upper level system...and a moisture fetch stretching back to 
the Great Lakes...snow is expected to extend as far east as the Blue 
Ridge Thursday night...though not in quantities seen on the Tennessee 
border. Winds may approach advisory criteria in the NC mountains 
Thursday night...and remain there into Saturday. On Friday snow 
levels rise to middle elevations...with some retreat from the Blue 
Ridge as the upper system passes. Snow levels fall again Friday 
night...but by that time moisture decreases to the point that only 
small probability of precipitation will be carried along the Tennessee border. Snow ends by 
Saturday morning...with winds diminishing as the pressure gradient 
relaxes. Sunday features dry high pressure. Temperatures will fall 
to several categories below normal on Friday in cold advection... 
despite a downslope component in the Lee of the mountains. As 
heights rise with the passage of the upper low...temperatures will 
warm toward normal values Saturday...reaching normal on Sunday. 


&& 


Aviation /15z Monday through Friday/... 
at kclt...IFR ceilings are expected to persist today...as moist 
isentropic upglide and drizzle persist. Model guidance indicates 
conditions deteriorating tonight to borderline IFR/LIFR ceilings and 
IFR visibility. Winds remain light out of the northeast. 


Elsewhere...today starts out with IFR ceilings...except at kavl 
with MVFR..and khky with LIFR. Expect to reach the bottom end of 
MVFR at SC sites and kavl by midday...with the upper end of IFR at 
khky. MVFR visibility is expected in drizzle east of the 
mountains...except MVFR at kand...with VFR in the mountains. Model 
guidance brings conditions down dramatically tonight...with IFR 
ceilings and visibility at SC sites...and LIFR at NC sites. Winds 
remain light from the northeast. 


Outlook...model guidance shows improvement Tuesday but most likely 
at best MVFR should be expected until Wednesday. A cold front will 
bring windy conditions on Thursday and a few restrictions in showers 
in the mountains. 


&& 


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


&& 


$$ 
Synopsis...jat 
near term...Arkansas 
short term...rwh 
long term...jat 
aviation...bsh/jat