810 
fxus62 kchs 240149 
afdchs 


Area forecast discussion 
National Weather Service Charleston SC 
949 PM EDT Wednesday Jul 23 2008 


Synopsis... 
an upper level disturbance and associated cold front will 
approach from the northwest overnight. The weakening front will 
stall just northwest of the area Thursday before dissipating. 
Atlantic high pressure will remain through the middle of next 
week...with weak low pressure across inland areas. 


&& 


Near term /until 6 am Thursday morning/... 
multicell clusters of thunderstorms will continue to advance east/southeast 
across the forecast area overnight...exiting to the east/NE late. 
Will continue to Divide probability of precipitation into two periods...with probability of precipitation 
initially tapered from chance/likely across the northern 2/3 of 
the forecast area to slight chance S...then...will graduate probability of precipitation 
from slight chance/chance north/NE to probability of precipitation below 15 percent west/SW 
for the balance of the night. 


Due to mesoscale boundary interactions and residual instability cannot 
rule out an an additional isolated pulse severe thunderstorm with 
damaging wet microbursts. However...due to diurnal stabilization the 
threat for severe thunderstorms will continue to wane tonight. 


Residual cloud cover produced by evening convection will limit 
the amount of cooling which will take place tonight...and expect 
lows in the lower to middle 70s away from the coast...and into the 
upper 70s/near 80 at the coast. 


&& 


Short term /6 am Thursday morning through Thursday night/... 
a cold front appears to stall and dissipate just northwest of the 
forecast area on Thursday. A southerly flow should persist at the 
surface...but the low to middle level flow should become northwest 
allowing some drier air to advect into the area. While the deep 
moisture will no longer be in place...there will be enough low 
level moisture to warrant forecasting a slight chance of 
showers/thunderstorms during the afternoon across much of the 
forecast area. Any convection will come to an end with the loss of 
daytime heating Thursday evening. 


Depending on the amount of residual cloudiness in place...highs 
could reach the lower 90s away from the coast on Thursday. Lows 
Thursday night should fall into the upper 60s to lower 70s. 


&& 


Long term /Friday through Wednesday/... 
a mean upper level trough will persist from eastern Canada southward 
through the Middle Atlantic States...while mean upper level ridging 
persists across the southwest and Southern Plains states. 


Models continue to differ in the details during the extended 
period. GFS is more aggressive with shortwave energy rounding the 
base of the upper trough...maintaining deeper level moisture 
across the forecast area. Despite model disagreement in some of 
the timing and strength of synoptic features....the general surface 
pattern is consistent between the models. An Atlantic ridge will 
linger over the marine zones...with a surface trough persisting 
inland. A gradual increase in moisture through early next 
week...in addition to the series of shortwaves moving into the 
southeast states...will maintain a chance of showers and 
thunderstorms during the afternoon and early evening hours through 
next Wednesday. 


Another frontal boundary will approach from the northwest late in 
the weekend through early next week. Considering the time of year 
and model solutions...the frontal boundary will likely stall just 
north of the region. Lacking any frontal passage...shower and 
thunderstorm activity is expected to remain mostly diurnal in 
nature. Best chance for convection will be within seabreeze 
forcing and instability during the afternoon/evenings...diminishing 
to a slight chance or less overnight. 


Afternoon heat indices are expected to trend upwards each day as 
low level moisture increases through the period. Heat indices in some 
locations could exceed 105 degrees from Sunday through at least 
Tuesday...as dewpoints will remain in the middle 70s during the 
afternoon hours. 


&& 


Aviation /02z Thursday through Monday/... 
thunderstorms could directly impact kchs and ksav with brief IFR 
or lower conditions and gusty/shifting winds before 06z. Expect 
taf amendments to address near term convective trends. 


Later tonight into early Thursday...low level moisture may support 
brief MVFR or lower visibility at either terminal. However...mid/high 
level clouds produced by convection may limit this potential. 


Isolated showers/thunderstorms may again develop on the sea breeze 
Thursday afternoon. However...the sea breeze may struggle to push 
inland...and limited mention of cumulonimbi to ksav after 20z. 


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... 
east of an inland surface trough...the surface pressure gradient 
remained tight across the coastal waters...supporting Small Craft 
Advisory winds across SC coastal waters north of Edisto 
Beach...outside Charleston Harbor...and across the outer Georgia 
waters. Per Wednesday evening trends...will extend scas for amz350 
and amz374 until 6 am. Synoptic winds will be altered by showers/ 
thunderstorms overnight. 


The marine zones will remain on the western periphery of Atlantic 
high pressure through the extended period. Winds will generally 
maintain a southerly component into next week. Speeds will remain 
at or below 15 knots outside of any thunderstorm activity...with 
seas at or below 4 feet. 


&& 


Chs watches/warnings/advisories... 
Georgia...none. 
SC...none. 
Marine...Small Craft Advisory until 6 am EDT Thursday for 
amz350-374. 


&& 


$$