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Area forecast discussion 
National Weather Service Greenville-Spartanburg SC 
647 PM EST Wednesday Mar 10 2010 


Synopsis... 
moisture will continue to spread across the area from the 
southwest...as a low pressure system approaches by the end of the 
week. This low will linger along the Carolina coast into the weekend 
before moving off to the northeast. High pressure will build back 
over the area by early next week. 


&& 


Near term /through Thursday/... 
a large area of rain has been moving slowly northward through the 
course of the day. The precipitation over SC and Georgia is a stratiform area of 
rain downshear from a persistent mesoscale convective system over northern Alabama and central Georgia. It 
is also being forced by good synoptic scale upper divergence. 
Subsidence and dry air over NC has kept the precipitation much making it much 
further north than the NC/SC state line...other than a few rain showers 
over the Piedmont earlier in the day. The models shift the upper 
divergence maximum NE...across the forecast area into the early evening hours...but 
it weakens quite a bit as well. This matches what we are seeing now 
as precipitation has been pushing further NE...but is also not as intense as 
earlier. 


Parts of NE Georgia have had around an inch of rain today. Light to 
moderate rain and showers should persist through the evening...but 
basin average rainfall rates won't be as high as earlier. 
Therefore...I Don/T see any flooding problems for this area and I 
won't issue a Flood Watch. By midnight the precipitation is expected to end 
or become very light across the forecast area as negative vorticity advection works across the region. 
At the same time...upper divergence will increase again along the 
central Gulf Coast as strong short wave over northern Texas lifts to the NE 
and a 180 knots jet moves across the deep south of the south side of 
the feature. 


This will rekindle convection along the Gulf Coast which will ride 
NE late tonight and during the day on Thursday. HPC favors the GFS/gefs 
solution which takes the bulk of the heavy rain with this next shot 
of forcing to our south. Most of the global models agree as 
well...though they aren/T quite as far south of the GFS. As 
convection is likely to develop along or just south of the deep cold 
pool laid down by today/S convection...these seems reasonable. The 
sref actually brings a precipitation bullseye across the forecast area during the afternoon 
hours tmrw. This is interesting...and Worth watching...but it has 
been discarded as a solution for this forecast. An isolated 
lightning strike or two is possible this evening and again on 
Thursday...but we will be well removed from surface based convection and 
the Richer boundary layer air which will stay south of the forecast 
area. 


&& 


Short term /Thursday night through Saturday night/... 
as of 230 PM Wednesday...huge upper low will begin to slowly drift 
eastward...ushering in a dry slot from the southwest Thursday night. 
Forecast soundings continue to show the bl remaining moist...so fog/drizzle 
may develop overnight if conditions are right. For now...will keep a 
low-end chance pop with mild temperatures. 


Friday and Friday night...12z models and ensembles in good agreement on 
the center of the low in vicinity of southeastern Missouri. As far as the surface 
forecasts...there is still a fair amount of spread. The 15z sref has nearly 
all members on board...with all showing at least some instability. The 
12z GFS has come in weak with the line and low on quantitative precipitation forecast and instability. 
The 12z European model (ecmwf)/Gem/NAM all show a strongly-forcing line entering the 
western NC mountains by Saturday evening. Considered going higher on pop with 
this line...but due to uncertainty of timing...kept it just likely 
for now. New day 3 Storm Prediction Center outlook has a "see text" for the western half of 
the County Warning Area. Will add mention of severe potential (as 7-8c/km middle level 
lapse rates should promote large hail). Shear is not that 
impressive...although the GFS has 300-500 m2/s2 0-3km helicity with the 
NAM around 300. This better low level shear is over the mountains where 
tornadoes are nearly unheard of (especially this early in the 
season). Temperatures will be mainly in the 60s to around 70 along the southeastern 
fringe. 


Saturday and Saturday night...models begin to diverge on the timing of 
the upper low passage across the central Appalachians. The GFS is on 
the slower side...not bringing the center over until after 12z 
Sunday. Using a model blend...do think the middle level cold pool will 
enter the NC Piedmont by middle-late afternoon. Even the 15z sref has a 
30-50% chance of 500+ j/kg of cape in that area. Will add mention of 
slight chance thunder for the NC Piedmont. Temperatures should be seasonable in 
westerly flow (a little below normal near mountain peaks). Overnight...low level 
thicknesses drop such that snow levels will likely drop to about 
3500 feet by daybreak Sunday. Moist westerly flow warrants a high-end chance 
pop overnight with some snow accums high elevs possible. Temperatures outside 
the mountains in the Lower-Middle 40s. 


&& 


Long term /Sunday through Wednesday/... 
as of 250 PM Wednesday...upper low will be slow to exit the eastern 
Seaboard...keeping the forecast area in westerly to northwesterly upper flow. Persistent 
moist low level upslope flow along the Tennessee/NC border is expected. 
However...thicknesses look too warm for more than periodic snow 
accumulate near mountain tops. Temperatures will be near normal east of the mountains and 
below normal in the mountains conditions along the Tennessee/NC border look to 
improve by Tuesday as high pressure finally builds into the Great 
Lakes and Ohio Valley. 


&& 


Aviation /00z Thursday through Monday/... 
at kclt...first batch of rain rain has moved east of the area and 
IFR ceilings should move out as well. Expect more showers and MVFR 
conditions to move in during the evening with IFR developing 
overnight. IFR in showers will continue through the day Thursday. Southerly 
winds tonight become northeasterly Thursday. 


Elsewhere...next batch of showers is moving back into the area. 
Expect IFR ceilings at the SC tafs through the period with VFR visibility 
becoming MVFR then IFR. VFR at kavl/khky will become MVFR overnight 
as showers move north. IFR develops during the day Thursday. Winds remain 
southerly at kavl...but become northeasterly overnight elsewhere. 


Outlook...expect a break in showers Thursday night...then more showers 
and thunderstorms move in Friday. Scattered showers and thunderstorms will continue to 
affect the region Sat and sun. Expect MVFR to IFR ceilings and visibilities 
through Friday with improving conditions late Sat-sun. 


&& 


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


&& 


$$ 
Synopsis...tjb 
near term...McAvoy 
short term...Arkansas 
long term...Arkansas 
aviation...McAvoy/rwh 

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