771 
fxus62 kchs 240728 
afdchs 


Area forecast discussion 
National Weather Service Charleston SC 
328 am EDT Thursday Jul 24 2008 


Synopsis... 
a weak cold front will stall out west of the area today and 
dissipate tonight. High pressure will extend across the region 
through early next week. 


&& 


Near term /through today/... 
early morning surface analysis shows a weakening cold front 
moving through the western Carolinas and northern Georgia with a 
pronounced Lee-side trough stretching from central Georgia through 
the central midlands and into eastern North Carolina. Isolated 
showers persist across the eastern midlands where low-level 
convergence is being enhanced by a weak mesoscale-low that has formed 
between Augusta and Columbia. This activity has shown signs of 
weakening during the past hour but a brief shower can not be ruled 
out from Hampton County up to Berkeley County through sunrise. The 
Lee-side trough and embedded mesoscale low will drift to the coast 
today as the cold front meanders east and eventually stalls out 
across the eastern midlands and the central Savannah River area. 


The prospects for measurable rainfall looks rather bleak today as 
the upper trough currently moving across the Carolinas is forecast 
to shift offshore by sunrise. Weak dnva in the wake of the upper 
trough coupled with extensive/deep dry air that is propagating 
quickly in from the west /per water vapor trends/ will tend to 
curtail convection despite temperatures rising into the lower 90s. 
Plan to maintain slight chance probability of precipitation from middle afternoon into early 
evening except for the far interior corridor from Millen and 
Allendale over to Smoaks and Harleyville where probability of precipitation will remain 
less than 15 percent. This regime is supported by both the 
GFS...the sref mean and to some extent the NAM...but the NAM mass 
fields appear to be heavily contaminated by convective feedback 
along the sea breeze. 


&& 


Short term /tonight/... 
any lingering evening convection will quickly dissipate after 
sunset. Wet grounds from recent rainfalls...extensive middle-level 
dry air and light/calm winds will support the development of 
patchy fog after midnight. Lows will range from around 70 well 
inland to the upper 70s at the beaches. 


&& 


Long term /Friday through Wednesday/... 
Friday trough Wednesday will be dominated by weak northwesterly 
flow aloft between the Southern Plains upper ridge and an upper 
level trough over the Great Lakes/northeastern states. At the 
surface...Lee side troughing mainly from central North Carolina to 
central Georgia will be common. 


Biggest challenge this forecast period is the probability of precipitation for Friday and 
Saturday. Eta model MOS and GFS MOS are now in agreement that probability of precipitation will be 
at or below 10 percent in just about all areas both days. Based on 
forecast soundings...this seems reasonable given decent cap with 700 
mb temperatures near 8 celsius and dry air aloft especially on 
Friday. Adjusted probability of precipitation down on both days from the previous 
forecast...but kept them above guidance enough to maintain slight 
chance probability of precipitation both afternoons. Have some concern that the models 
maintain the drier air aloft too long and this results in lower probability of precipitation 
than would normally be the case. In addition...have some concern 
that there will be enough convergence along the sea breeze to 
overcome the cap in a few locations both days. 


Deeper moisture is expected to return Saturday night and remain with 
US through at least Wednesday. This combined with surface dewpoints 
at least in the lower to middle 70s and upper level disturbances moving 
across the area should be enough to result in mainly scattered 
afternoon and evening showers and thunderstorms. 


&& 


Aviation /06z Thursday through Monday/... 
kchs - the main line of showers and thunderstorms has pushed east 
of the terminal although some isolated activity remains across the 
midlands. This activity is expected to dissipate before reaching 
the chs airspace...but trends will be carefully watched in case an 
amendment is needed to include precipitation in the chs taf. Middle-high level 
cloudiness will gradually thin out this morning but there should 
be enough preclude significant fog formation through sunrise. The 
fog potential is not non-zero since the grounds are wet from earlier 
rains. Will carry a tempo 5sm br group from 09-12z to cover this 
possibility. Otherwise VFR conditions will prevail for the next 24 
hours. 


Ksav - extensive middle-high level cloudiness remains in place this 
morning. Satellite and surface observations indicate a broken deck 
around 4000-5000 feet is slowly expanding in coverage from vdi-tbr. 
This area of enhanced cloud cover should reach the sav terminal 
by 09z and remain in place through sunrise. This should preclude 
significant fog development so fog will be removed from the sav 
taf with the 06z cycle. VFR conditions will prevail for the next 
24 hours. 


Extended aviation outlook...a chance of MVFR visibilities each morning 
due to high low level moisture and light winds...otherwise VFR 
conditions expected outside of mainly afternoon/evening convection. 


&& 


Marine... 
winds across the South Carolina waters are being heavily 
influences by convection that is lingering off the Charleston 
County. These influences should diminish over the next few hours 
as the convective complex pushes farther offshore. Across the 
Georgia waters...a bit of a surge continues but speeds have 
recently dropped below Small Craft Advisory criteria. Will 
therefore cancel the advisory a few hours early. Otherwise expect 
winds to recover more southerly today as a cold front remains well 
to the west and a weak Lee-side trough meanders just inland from 
the coast. Southerly winds will persist into tonight but both 
speeds and the resulting seas will remain well below advisory 
criteria. 


A fairly tranquil period is expected from Friday through Monday 
as a weak pressure gradient dominates and results in mainly 
southerly to southwesterly winds at or below 15 knots. Seas will 
be at or below 3 feet within 20 miles of the coast and at or below 4 feet in 
amz374. 


&& 


Chs watches/warnings/advisories... 
Georgia...none. 
SC...none. 
Marine...none. 


&& 


$$ 


St/mte 

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