688 
fxus62 kchs 231152 
afdchs 


Area forecast discussion 
National Weather Service Charleston SC 
652 am EST Monday Nov 23 2009 


Synopsis... 
an area of low pressure off the coast early this morning...will lift NE 
of our region today. Meanwhile...a high pressure wedge will remain firmly 
entrenched over South Carolina and southeast Georgia through Wednesday night. A 
cold front will then push through the area Thanksgiving day... 
followed by high pressure building back into the region from the west 
through the weekend. 


&& 


Near term /through tonight/... 
a surface low 40-60 miles east of the Savannah River entrance this morning 
is expected to quickly move NE off the Carolina coast today and 
likely reach the Outer Banks by early this evening. Areas of light 
rain were moving NE over the southern midlands around dawn. A few 
patches of light rain were noted on radar over our South Carolina 
zones...with areas of drizzle and a couple of sprinkles elsewhere. 
Over much of our forecast area. Temperatures remaining relatively 
steady...just about everywhere is in the lower or middle 50s. 


The Wedge may tilt a bit more vertical as the wave off the coast 
moves off the southeast North Carolina coast a bit later on...and this 
could cause temperatures to remain locked in the middle or upper 50s 
to the west of I-95 in both South Carolina and Georgia this afternoon. 
A weak late day boundary layer downslope and morning warm air 
advection show a potential for readings breaking 60 in parts of 
the Charleston tri-County area...but not by much. 


Not a lot of measurable precipitation today...sprinkles and drizzle for 
many areas under cloudy skies and light north winds. 


&& 


Short term / Tuesday through 6 am Tuesday/... 
plenty of low clouds...patchy drizzle and areas of fog will be 
the rule. Diurnal temperature variations should be fairly small 
with The Wedge solidly in place. Low level geostrophic flow will 
be light tonight and a build-down fog situation may pose a risk 
for dense fog development. We have continued mentions of fog in 
our forecast but dense fog advisories are certainly possible over 
parts of our forecast area. 


&& 


Long term /Tuesday through Sunday/... 
medium range guidance is in fairly good agreement throughout the 
extended periods this morning. Model solutions continue to depict 
high pressure wedging entrenched in the Lee of the Appalachians 
Tuesday through Wednesday night...before a broad upper level trough 
dives southeastward into the region for Thanksgiving day...bringing 
an end to the rather cool and dreary conditions across the low 
country. 


Before the stagnant air mass gets kicked eastward and out of 
the region on Thanksgiving day...expect mainly cloudy skies and cool 
temperatures to prevail. Model solutions are in fairly good 
agreement showing an area of low pressure tracking northeastward off 
the Georgia and Carolina coast Wednesday and Wednesday night...so 
have expanded probability of precipitation to include the entire forecast area. Will keep 
probability of precipitation in the slight chance range though...as most activity will 
likely remain in closer proximity to the Gulf Stream. 


Thanksgiving day a surface cold front swings through in advance of 
the broader upper level trough...allowing boundary layer winds to 
increase out of the west and breaking down the stubborn high 
pressure wedge. High pressure will then slowly build into the region 
from the west Thursday night through the upcoming weekend...with a 
couple dry re-enforcing cold fronts moving through the area Thursday 
night through Friday night. The coldest air mass of the season is 
likely to settle over the low country Friday through Saturday...and 
although maximum temperatures won't be terribly cold...overnight 
lows Friday night and Saturday night will dip into the 30s across 
most locales...and frost/freeze headlines may eventually be needed. 


&& 


Aviation /12z Monday through Friday/... 
IFR ceilings locked in over Georgia and the Carolinas at daybreak with 
improvement today to be gradual at best given 06z forecast soundings 
at both kchs and ksav. We continue to show a small afternoon window 
for ceilings to lift to MVFR but recent numerical guidance has trended 
pessimistic. IFR visibilities at daybreak should become MVFR by late 
morning...possibly p6sm for a period this afternoon. 


Tonight...stratus is expected to expand and lower quickly this evening 
and IFR ceilings will again develop at both terms and build down overnight. 
We have capped visibilities at 1sm on this taf cycle but 1/4 mile visibilities 
and restricted vertical visibilities are certainly possible tonight in vicinity of of 
both airports. 


Extended aviation outlook...IFR/MVFR likely through Wednesday. VFR conditions 
should become prevalent Thursday through Friday. 


&& 


Marine... 
winds have ebbed along the South Carolina coast overnight. Recent 
discussion with the Charleston pilot office indicated 20 knots flow 
earlier in the night has subsided to 10 to 15 knots around The Harbor 
at press time. Similar story right along the upper Georgia coast 
as observations indicating a decreasing trend. Along the South 
Carolina coast...we are going to let the Small Craft Advisory ride 
a while longer this morning as seas remain elevated and the fetch 
is favorable for a slower downward trend on seas. Even at Grays 
Reef...seas still close to 5 feet at 3 am. 


As the low pulls NE today...winds should become north or north-northwest most 
locations with seas coming down to 3 to 4 feet near shore and 
4-5 feet well offshore this afternoon. Tonight...a bit of a late 
night north surge possible and speeds may reach 15 knots off the Georgia 
coast after midnight. 


A wedge of high pressure inland will keep a northerly flow in 
place over the coastal waters Tuesday through Wednesday night 
with winds less than 15 knots. A cold front will shift offshore 
Thursday...with strong cold air advection developing in its wake. 
This could result in the development of Small Craft Advisory 
conditions...especially over the outer Georgia waters...by late in 
the work week. 


&& 


Chs watches/warnings/advisories... 
Georgia...none. 
SC...none. 
Marine...Small Craft Advisory until 11 am EST this morning for amz350- 
352-374. 


&& 


$$ 

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