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fxus62 kgsp 181831 
afdgsp 


Area forecast discussion 
National Weather Service Greenville-Spartanburg SC 
231 PM EDT Friday Jul 18 2008 


Synopsis... 
an area of low pressure situated just off the southeast coast is 
expected to move northeast along the coastline of the Carolinas this 
weekend. A weak cold front is then expected to move into the region 
Monday night into Tuesday...stalling out across the Piedmont by the 
middle of next week. 


&& 


Near term /through Saturday/... 
the immediate concern is the band of showers and storms at the outer 
edge of the circulation around the low pressure developing along the 
Georgia coast. There remains a tight moisture gradient...thus a tight 
instability gradient...just ahead of the band. If this does not 
change...the convection will quickly run out of fuel before it 
reaches the Charlotte metropolitan area. A slight chance pop will be 
carried on this fringe of the County Warning Area to handle this possibility through 
the middle part of the evening...otherwise tonight should be dry 
with most of the forecast area under weak subsidence. The low temperature 
forecast was nudged toward the warmer met guidance accordingly. As 
for Saturday...the models take the low along the coast which brings 
the moisture gradient and some low level convergence as far west as 
roughly I-77. The previous forecast had a slight chance over the 
east and that will be kept as it is in agreement with neighbors. 
Temperatures were nudged up over most of the area with the expectation that 
subsidence/downslope would keep US on the warm side of guidance. 


&& 


Short term /Saturday night through Monday night/... 
as of 200 PM Friday...sensible weather for Sunday still looks like it 
will remain limited to just diurnally fired isolated mountain thunderstorms with 
downslope aided warming and drying across the fthls/Piedmont behind 
the central Carolinas surface trough. Upper pattern does not change 
very much into Monday...broadly diffluent northwest flow. Nominal 
increase in moisture ahead of southward dropping cold front 
should give rise to a greater threat of afternoon thunderstorms... 
although both the ec and GFS response is still limited. Will 
plan on maintaining just a slight chance along with above normal 
temperatures. 


&& 


Long term /Tuesday through Thursday/... 
as of 130 PM Friday...I have made very few changes to the going 
forecast as it still appears to reflect the updated HPC thinking for 
the medium range. Again...the European model (ecmwf) has primarily been relied upon 
for the details of the forecast. Aloft...the eastern Continental U.S. Will 
maintain some degree of troughing Tuesday through Friday as an upper vortex 
spins over eastern Canada. At the surface...the main feature for the 
period will be a frontal boundary that approaches the forecast area on 
Tuesday...then sags southward across the region through the middle of 
the week. The 00z/18 European model (ecmwf) depicts the band of deepest moisture 
along the front clearing the forecast area to the south Wednesday night which seems a 
little aggressive. Instead...I would favor a solution more like HPC 
that features the boundary essentially washing out and remaining in 
the vicinity of the forecast area. Then by Thursday...the boundary looks to begin 
to lift back north...though remaining across the Carolinas through 
the end of the week. At any rate...this front should provide a 
trigger and focusing mechanism for mainly diurnal convection across 
the forecast area. Therefore...expect scattered afternoon and evening 
convection across the County Warning Area with some convection continuing into the 
overnight hours. Warmest temperatures...low 90s Piedmont upper 80s 
mnts...on Tuesday ahead of the approaching front. The rest of the 
period looks a few degrees cooler and closer to climatology with increased 
cloud cover near the front and some slightly cooler air behind it 
Wednesday through Friday. 


&& 


Aviation /19z Friday through Wednesday/... 
the main issue concerning the tafs is what to do about the precipitation 
band that has developed at the outer edge of the low pressure system 
off the Georgia coast in terms of how it will affect kclt. Surface 
observations show a tight gradient of moisture and instability 
between kclt and the location of the precipitation band...meaning the band 
will be moving into significantly less favorable air during the 
afternoon unless the low level environment near kclt is modified. 
Upstream observations suggest that relatively dry air will continue 
to be advected over kclt this afternoon. Kclt will probably be in 
and out of a ceiling around 5k feet this afternoon...but for right now 
the most likely outcome is for the precipitation band to die out just 
before it gets to kclt in the late afternoon/early evening. The 
instability gradient will be monitored for signs of movement and the 
kclt taf will be amended accordingly if the probability of precipitation 
improves. Otherwise...VFR conditions will persist through the late 
night hours...but some MVFR visibility issues can be expected once 
again at kavl and khky. The low may make its closest approach to 
kclt on Saturday morning which could push an MVFR ceiling over that 
site...similar to what was seen closer to the coast this past 
morning. The MVFR conditions should improve by middle morning. 


Outlook...early morning fog at kavl will probably result in MVFR 
conditions Sunday morning and Monday morning. As we remain in this 
air mass...air quality should get poorer each day leading to an 
increased chance of MVFR haze at the other taf sites each morning. A 
front will drop in Tuesday and Wednesday bringing scattered 
thunderstorms. 


&& 


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


&& 


$$ 
Synopsis...bsh 
near term...PM 
short term...csh 
long term...bsh 
aviation...PM