193 
fxus62 kchs 081139 
afdchs 


Area forecast discussion 
National Weather Service Charleston SC 
639 am EST Thursday Jan 8 2009 


Synopsis... 
high pressure will remain southwest of the area today while a dry 
cold front moves through the area. High pressure will then build 
in from the west tonight and move across the area through Sat. 
Another cold front will approach from the west Sat afternoon and move 
through the area Sat night. Colder high pressure will then settle 
over the area for early next week. 


&& 


Near term /until 6 PM this evening/... 
a much drier and cooler airmass is in place within strong cold air 
advection behind a cold front now well offshore. Of note however 
is a potent upper level shortwave that will swing through the area 
by midday today. Although the lower levels are significantly 
drier...enough midlvl moisture will be associated with this wave 
to have increasing clouds this morning. This may be enough to 
inhibit warming to some degree but will overall look for maximum temperatures 
to reach the middle 60s...which is generally below MOS guidance 
across the board. Clouds will gradually dissipate by late this 
afternoon as the shortwave moves offshore. 


Breezy conditions will again be the case today...but not to the 
degree that was seen yesterday with the deep layered wind fields. H925 
winds of 30-40kt will partially mix down to the surface...creating surface 
winds of 15-25 miles per hour with occasional higher gusts. Winds will settle down 
by this evening as the inversion develops and prime mixing ceases. 


Lake winds...winds will respond at Lake Moultrie today... 
particularly after midday and around the warmer Lake Shores 
where mixing will be deepest. West-southwest flow today 15-25 knots with occasional 
gusts near 30 knots during peak heating. 


&& 


Short term /6 PM this evening through 6 am Friday/... 
clear and colder conditions will prevail tonight as high pressure 
moves in during another bout of cold air advection. Winds will 
settle down and by the early morning hours rather good radiational 
cooling conditions will develop. This will force overnight lows 
away from the coast to drop to the lower 30s north and the middle 30s S. 
Near the coast...lows will bottom out around 40 degrees. 


Lake winds...we extended lake Wind Advisory conditions until middle 
evening but winds and waves should begin to subside overnight as 
low level wind fields gradually diminish. 


&& 


Long term /Friday through Wednesday/... 
cool high pressure will slide across the area Friday into Sat. With 
weak northwesterly upper level flow in place...maximum temperatures Friday will only 
reach the middle 50s to lower 60s. As high pressure shifts offshore 
Friday night into Sat...min temperatures Friday night will not be quite so 
cool...reaching the 35-40 degree range away from the coast. 


Sat will see an increase in clouds as another cold front 
approaches from the west. There will also bea brief return of warm 
air advection as deeper southwesterly flow develops behind the offshore 
high pressure area and an approaching upper level shortwave 
trough. This will allow maximum temperatures to jump to the 65-70 degree 
range before clouds make enough of an impact to halt the rising 
temperatures. Although there are some timing differences among the 
models...enough agreement is there to mention 20/30 probability of precipitation for Sat 
afternoon. The GFS looks to be the fastest while NAM/European model (ecmwf) looks 
slowest. 


There is good agreement that the front will move through the area 
Sat night...along with a deeper swath of moisture that will 
approach the coast ahead of the front. Best timing puts the precipitation 
through the area by 06z...so have only highlighted probability of precipitation for Sat 
evening with a dry forecast for the remainder of Sat night. Have nudged 
probability of precipitation into the 40s which is higher than the previous pkg but still 
below model guidance which advertises low-end likely probability of precipitation. Given 
the impressive precipitation forecasts that the models had with the recent 
event and its poor turnout...am not ready to raise probability of precipitation any higher 
than 40 percent. As for temperatures...cold air advection does not kick 
in until midday sun so min temperatures Sat night will again trend 
warmer...reaching the lower 40s. 


High pressure returns starting sun as does a few bouts of cold air 
advection that will drop temperatures well below normal levels. Will 
advertise maximum temperatures in the upper 50s sun-Monday with lows in the 
upper 20s to middle 30s. A dry cold front will move through late Monday 
night...and this will bring in a noticeable drop in temperatures for Tuesday- 
Wednesday. Using 1000-850 mb thickness tools GOES so far as to show maximum 
temperatures only in the 30s with lows in the teens...but am not going 
quite that cold though have opted to drop temperatures a few categories 
during this dry cold spell. Have shown maximum temperatures reaching only the 
middle-upper 40s with mins in the low-middle 20s. 


&& 


Aviation /12z Thursday through Monday/... 
VFR conditions at both ksav and kchs through tonight. Prevailing 
wind gusts in the middle/upper 20 knots range are expected late morning 
and afternoon hours today as vertical mixing taps into continued 
strong low level wind fields. Winds should gradually Ebb overnight 
after prevailing gusts shut off around or shortly after sunset. 


Extended aviation outlook...VFR conditions will prevail until the 
possibility of MVFR conditions on Sat/Sat evening. VFR conditions 
anticipated Sunday and Monday. 


&& 


Marine... 
Small Craft Advisory conditions over waters beyond 20 nm early 
this morning will translate back to near the land/sea interface 
this afternoon as gusty west-southwest winds redevelop ahead of the next 
cold front. By middle to late afternoon...frequent gusts reaching 
25 knots should extend from coastal Charleston County S to the 
intracoastal and near shore region of southeast Georgia. Cooler waters 
will likely have to wait until late day before marginal Small 
Craft Advisory conditions develop. Our warmest waters beyond 40 
nm east-southeast of Savannah will remain in/near Small Craft Advisory criteria though much 
of tonight. Initializing with Small Craft Advisory all waters including the 
Charleston Harbor this morning. 


Winds and seas should quickly come down early Friday as high pressure 
settles over Georgia and the Carolinas by afternoon. A fast-paced 
surface and upper pattern will persist over the weekend into Monday. 
The next frontal passage is still slated for Sat night and a short 
lived surge should ensue but end by midday Sunday as high pressure 
rebuilds. Flows backs and increases again later Monday ahead of the 
next strong cold front. 


&& 


Fire weather... 
deep-layered mixing will promote breezy conditions across the 
entire area today as an upper level shortwave swings through the 
area. 925mb /about 2000 feet/ winds of 30-40 knots should be able to 
mix down to the surface as mixing heights will be in the 3500-4500 feet 
range...creating 20 feet winds of around 15-25 miles per hour with gusts to 30 
miles per hour. In addition...relative humidity values look to drop to the 26-29 percent 
range...which when combined with relatively dry fuels will make 
for near red flag conditions today. 


Users were contacted yesterday and after coordination...a fire 
danger statement was issued. Since conditions are not quite red 
flag...will maintain the fire danger statement. Should conditions 
worsen or users opt otherwise...a red flag warning may still be 
issued. 


&& 


Chs watches/warnings/advisories... 
Georgia...none. 
SC...lake Wind Advisory until 11 PM EST this evening for scz045. 
Marine...Small Craft Advisory until 10 PM EST this evening for amz350- 
352-354. 
Small Craft Advisory until 5 am EST Friday for amz374. 
Small Craft Advisory until 6 PM EST this afternoon for amz330. 


&& 


$$ 

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