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Area forecast discussion 
National Weather Service Greenville-Spartanburg SC 
237 PM EDT Tuesday Mar 16 2010 


Synopsis... 
a weak trough of low pressure will persist over the southern 
Appalachians through Wednesday. High pressure will slowly return 
from the west across the western Carolinas and northeast Georgia 
Thursday then move off the Carolina coast Saturday. A sharp cold 
front will cross the Mississippi Valley late Saturday and move 
eastward through our region on Sunday. High pressure returns on 
Monday. 


&& 


Near term /through Wednesday/... 
a flat upper ridge will move off the Carolina coast tonight...as an 
upper low moves along the Gulf Coast from Texas to the Florida Panhandle. 
This low moves to the SC coast on Wednesday. Surface ridging moves 
east across the Appalachians tonight...causing surface winds to veer 
form north to northeast...resulting in a moist upslope flow into the 
southern Appalachians. Cloud cover will increase this evening...and 
a small probability of precipitation will be carried in the west both tonight and Wednesday. 


Initially...model soundings are rather warm at the top of the moist 
layer...but with time moisture depth increases ot the point where 
the GFS is around minus 8 degrees c...and the NAM minus 5 degrees c. 
A top down approach using the GFS yields liquid precipitation... 
except for some isolated freezing rain where surface temperatures 
support it at the very highest elevations. Temperatures both tonight 
and Wednesday will exhibit a limited diurnal range under cloud cover. 


&& 


Short term /Wednesday night through Friday/... 
as of 230 PM Tuesday...HPC favors the GFS and European model (ecmwf) while 
considering the NAM an outlier. With this in mind expect another 
shortwave to dig into the lower MS valley Wednesday night and pass S of 
the area Thursday. Best dynamics and moisture remain well S of the County Warning Area 
but expect weak forcing and deep enough moisture for slight chance probability of precipitation 
over the NC mountains...plus the foothills and Piedmont SW of I-26. 
Vertical temperature profiles indicate light snow will be possible higher mountains 
Wednesday night. Low level moisture should scatter out during the day Thursday 
as ridge builds in from the northwest...with maximum temperatures warming a category 
or so above average. Ridge axis builds over the southeast US Friday with SW flow 
developing in the afternoon. This should allow temperatures to warm to near 70 
across the Piedmont with 55 to 65 over the mountains 


&& 


Long term /Friday night through Tuesday/... 
as of 230 PM Tuesday...the medium range models are in fairly good 
agreement in are generally delaying the arrival of the next front. 
The Gem is a bit faster in bringing in the frontal convection and by 
00z Monday has it moving across eastern North Carolina. Prior to 
that however...the models agree on no precipitation Friday night and with 
the upslope flow from the Gulf on Saturday there will be a gradual 
increase in showers over the southern extent of the mountains. 
There is a marked increase in wind speed ahead of this front with 35 
to 50 knot wind at 850mb on the GFS and European model (ecmwf) for much of Sunday. 
Considering the wind shear and just a bit of cape...I maintained 
isolated thunder upper Savannah valley Sunday morning and middle day 
and slight change thunder south of Charlotte Sunday afternoon. 
Confidence rather low on wrap around northwest flow producing much 
at this time but bares watching. Dry otherwise Monday through 
Tuesday night with high pressure settling in with decreasing wind 
Tuesday. 


&& 


Aviation /19z Tuesday through Sunday/... 
at kclt...north winds of 6-9 kts will veer to the northeast by this 
evening...decreasing to around 5 knots. A low VFR ceiling will 
persist through midday Wednesday in a weak upslope flow. 


At kavl...the MVFR ceiling is expected to lift to VFR this 
afternoon...then decrease to MVFR after midnight. Model guidance 
suggests that pooling of cool moist air in the valley will support 
MVFR fog formation by dawn. Conditions return to VFR Wednesday 
morning as fog dissipates and the ceiling lifts. Precipitation 
associated with a weak upslope flow from the east will be to 
scattered to mention in the taf at this point. 


Elsewhere across the forecast area...light north winds will gradually veer to 
northeast...however kand may remain light and variable until 
Wednesday. Low VFR ceilings will move into the area from the 
northeast. Any precipitation that forms near the Blue Ridge due to 
upslope flow on Wednesday will be too isolated to mention in the 
tafs. 


Outlook...flight conditions across the western Carolinas will 
generally remain VFR through middle week. The mountain valleys could 
experience sub-VFR ceilings and visibilities during the early 
morning hours Thursday. 


&& 


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


&& 


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