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Area forecast discussion 
National Weather Service Greenville-Spartanburg SC 
245 PM EDT Friday Mar 19 2010 


Synopsis... 
weak but warmer high pressure will remain over our region through 
Saturday...before moving off the Carolina coast. A cold front is 
expected to cross the western Carolinas and northeast Georgia from 
the west late Sunday with an upper level low passing over on Monday. 
High pressure will again be the main influence from Tuesday through 
Thursday. 


&& 


Near term /through Saturday/... 
an upper level ridge axis continues to slowly approach the 
appalachian chain from the west...as highly positively-tilted trough 
moves into the Central Plains states. Visible satellite imagery 
shows clear skies for hundreds of miles in every direction...as surface 
ridge dominates the southeast U.S. Weather. Expect nearly ideal 
radiational cooling conditions tonight...with temperatures dropping about 
30 degrees from today/S highs. 


Saturday...high pressure system shifts eastward...resulting in 
return flow across the forecast area. A slight increase in low level 
moisture will result in cumulus development mainly across the mountains 
during the afternoon. A few clouds may develop out across the lower 
Piedmont by evening as southwesterly low level flow strengthens. In 
any case...highs should be about the same or a couple degrees warmer 
than Friday/S. 


&& 


Short term /Saturday night through Monday night/... 
most of the short range models are in good agreement in bringing a 
shot of middle and upper level forcing in the form of good upper 
divergence and middle-level frontogenesis across the region from late 
Sunday morning into the afternoon hours. The llvls Don/T respond as 
quickly...though increasing upslope flow should help to develop precipitation 
over the southern mountains of NC...NE Georgia and the western upstate. Precipitation will have 
trouble making it much further east than an Asheville to Greenville 
and Greenwood line during the day. I have a small area of half an 
inch of quantitative precipitation forecast centered over the northwest upstate...southern Appalachians and NE 
Georgia during the afternoon hours...with quantitative precipitation forecast decreasing considerably away 
from this area. There is only a little cape in the model soundings. 
I/M skeptical about any convection...but I/ll hold on to slight 
chances in the afternoon hours over SC and Georgia zones...and remove thunder 
farther to the north. Severe storms are not anticipated. 


Dry air overspreads the region above 700 mb Sunday evening...though 
warm advection will increase in the llvls as an east-southeast oriented low level 
jet strengthens. This will again favor the mountains and adjacent 
foothill locations for the heavier rain...though the forcing over 
the eastern zones increases enough late at night that precipitation chances 
should be pretty high along the I-77 corridor as well. The overall 
precipitation amounts will be fairly light...with a quarter inch or less away 
from the areas with heavier upslope-enhanced precipitation rates. Thunder 
again looks doubtful. However...with the dry air and cooling temperatures 
aloft as the southern stream closed low approaches from the west...I/ll 
keep slight chances in though the early morning hours Monday across 
the forecast area. 


The European model (ecmwf) and GFS are in good agreement in taking the 500 mb upper low 
right across the forecast area during the day on Monday. The steep lapse 
rates...coupled with at least a little afternoon heating...should be 
good for scattered rain showers and even a few thunderstorms. The best coverage will be 
over the mountains freezing levels will be high enough that any snow 
should be confined to elevations above 4500 feet. The ec and GFS 
keep the best deformation zone forcing a little north of the forecast area as 
the low crosses. Therefore I Don/T see enough forcing for widespread 
high elevation heavy snow. However...when an upper low this strong 
crosses directly overhead...there are often some surprises in the 
high elevation snow department. The bottom line to all this is that 
the highest NC mountains elevations could see another 2 to 3 inches of 
wet snow. 


The upper low will pull east of the region Monday night. Layer relative humidity/S 
decrease and temperatures warm aloft. Northwest flow will strengthen along the Tennessee 
line...but 800 mb temperatures will be very warm...generally from 0 to -3 degree 
c. Showers will likely persist across the mountains...but this should cut 
down on any accumulating snowfall. However a southerly jog to the 
deformation zone would keep the northern mountains under better forcing for a 
longer period of time. 


&& 


Long term /Tuesday through Friday/... 
as of 230 PM Friday...at 12z Tuesday the upper low is shown by the 
Gem...GFS and European model (ecmwf) to be over eastern North Carolina with the European model (ecmwf) 
having it the farthest south...maybe closer to Myrtle Beach. The 
wrap around moisture decreases through the middle day hours over the 
mountains and the last remains of moisture are gone by late 
afternoon...except the European model (ecmwf) holds on for northern mountains into 
the evening. Heights will be warming as the upper low gets more 
east of our area. Weak high pressure will be centered over our 
region on Wednesday and highs will be about a category above 
normal. As the next system approaches from the west late in the 
week...seems the European model (ecmwf) is performing better than yesterday. The 
European model (ecmwf) is now outpacing the others. Also...a significant change in 
thunder potential. The low and stronger shortwave should pass 
from Tennessee Thursday night to Virginia/North Carolina late 
Friday. Wind shear is now indicated to be stronger and cape values 
in the 200 to 700 range are expected from northeast Georgia and the 
southwest North Carolina mountains to the southwest half of the 
upstate late Friday. Adding thunder to these areas matches up well 
with our western neighbors. The system starts to go east of our 
forecast area to start the weekend. 


&& 


Aviation /19z Friday through Wednesday/... 
at kclt...VFR with no restrictions next 24 hours. Light northwest winds 
still expected to shift to SW around 21z and remain light. 


Elsewhere...winds less than 8 kts and mostly clear conditions 
expected through the period. 


Outlook...VFR is expected through Saturday night. A cold front will 
bring restrictions with a line of showers and thunderstorms Sunday 
into Sunday night. Lingering rain/snow showers in the mountains and gusty 
southwesterly/westerly winds over the Piedmont expected on Monday. 


&& 


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


&& 


$$ 
Synopsis...deo 
near term...Arkansas 
short term...McAvoy 
long term...deo 
aviation...Arkansas 

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