616 
fxus62 kgsp 171810 
afdgsp 


Area forecast discussion 
National Weather Service Greenville-Spartanburg SC 
210 PM EDT Wednesday Mar 17 2010 


Synopsis... 
low pressure will move away from the southeast coast tonight and 
Thursday. High pressure will build over the area Friday and 
gradually move off the Carolina coast by Sunday morning. A cold 
front will move into the Mississippi Valley Saturday and then cross 
the western Carolinas and northeast Georgia on Sunday. Cool high 
pressure will return to the region Monday through Tuesday. 


&& 


Near term /through Thursday/... 
a closed upper low will move slowly east from Georgia to the Gulf Stream 
by Thursday. Meanwhile an associated surface low will move northeast 
along the Gulf Stream off the Carolina coast. Northeasterly flow 
around the north side of the low will continue to produce an upslope 
component into the southern Appalachians...resulting in clouds and a 
small chance of precipitation in the mountains and foothills...but 
will also bring dry low level air to the Piedmont of NC. As middle 
levels moisten at ice nucleation temperatures...model soundings 
become more supportive of snow at higher elevations late tonight. 
Probability of precipitation will decrease on Thursday as drier low level air reaches the 
foothills. Minimum temperatures will run near normal tonight...as 
cloud cover offsets the lower heights associated with the closed 
low. Maximum temperatures will be above normal on Thursday as 
heights rise in the wake of the low and winds back from northeast to 
north...setting a downslope flow in the Lee of the mountains. 


&& 


Short term /Thursday night through Saturday/... 
as of 155 PM Wednesday...all the models agree on drying out the 
atmosphere Thursday night with northerly downslope wind for 
locations on the downslope side of the mountains. The NAM and GFS 
show a bit of remaining moisture along the Tennessee side at 00z 
Friday but all that is gone before 06z. Decided to leave out any 
pop for Thursday evening period after 00z. Upper trough or cut off 
weak low moves east and off the Carolina coast Friday morning as 
heights build in from the west. Stronger southerly flow does not 
arrive until very late Friday or even Friday night. Still expect 
temperatures well into the 60s for the mountains and 70 to 74 for 
the foothills and Piedmont. Nearly all models have US in the axis 
of the upper ridge around 00z Saturday. The GFS...sref...Gem and 
European model (ecmwf) all show the approach of the frontal precipitation from the west on 
Saturday with some variations in the timing of the onset of the 
rain. Certainly most of the precipitation will be well after 00z 
Sunday...but considering upslope flow increasing late Saturday and 
one of the soundings showing brief rain at Anderson earlier...felt 
it best to include slight chance for the favored upslope areas late 
Saturday. Temperatures should be about the same Friday and Saturday 
in the afternoon. 


&& 


Long term /Saturday night through Tuesday/... 
as of 205 PM Wednesday...a blend of the slower European model (ecmwf) and faster GFS 
is the favored HPC solution for the extended period. 500 mb shortwave 
over plains will track east across the MS valley Sat night and into the 
County Warning Area sun. Associated cold front will push into County Warning Area during the day sun. As 
the system approaches...deep moisture will surge north with good 
isentropic lift and upper level divergence so expect an incrsng chance 
of showers Sat night...becmg likely across most of the County Warning Area after 
daybreak sun. Expect decent lapse rates with temperatures in the 60s across 
the Piedmont Sun afternoon. With incrsng shear and weak cape expect a 
slight chance of thunderstorms across the County Warning Area Sun afternoon-early evening. Precipitation should 
slowly taper off from the west Sun night with lows cooling into the low 
40s...30s mountains and there will be a chance of snow at the higher elevs 
overnight with no sig accumulate expected. Showers will linger Monday as a 
weak reinforcing shortwave moves across the County Warning Area from the northwest...mainly 
over the NC mountains and foothills. Temperatures should be a Cat or two below 
average Monday...warming to near average Tuesday as ridge builds over the Region. 
Ridge axis moves offhsore Tuesday night-Wednesday with warm SW flow developing 
ahead of next system and temperatures Wednesday are expected to warm to above average. 


&& 


Aviation /18z Wednesday through Monday/... 
at kclt...cirrus will increase form the west today....remaining 
overhead through midday Thursday as an upper low moves from Georgia to 
the Atlantic. Model time heights suggest broken middle cloud beneath 
the cirrus...but observations and satellite imagery do not support 
this. Light winds will gradually back from east southeast this 
afternoon...to east northeast this evening...to north late tonight 
and Thursday. 


Elsewhere across the forecast area...VFR stratus will remain across the 
mountains through midday Thursday as a result of low level upslope 
flow. Drier low level air from the northeast will gradually work its 
way west into the foothills...first in NC...then SC...eroding the 
stratus layer. Extensive cirrus will remain above this layer. 
Observations and satellite imagery do not support the moist middle 
levels of the models. Light winds will gradually back from east 
today to north Thursday at foothills sites...while kavl remains 
light and variable today...and becomes light northerly Thursday. The 
met guidance supports fog restrictions at kavl Thursday morning... 
but the mav does not...and the taf will remain VFR for now. 


Outlook...VFR is expected through Saturday. A cold front may bring 
restrictions with a line of showers and thunderstorms on Sunday. 


&& 


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


&& 


$$ 
Synopsis...deo 
near term...jat 
short term...deo 
long term...rb 
aviation...jat