608 
fxus62 kchs 161931 
afdchs 


Area forecast discussion 
National Weather Service Charleston SC 
331 PM EDT Tuesday Mar 16 2010 


Synopsis... 
weak high pressure will shift offshore tonight. Low pressure will 
cross the Florida Peninsula Wednesday and develop offshore 
Wednesday night into Thursday. High pressure will then build into 
the area Friday through Saturday. A cold front is expected to move 
through the region Sunday...followed by high pressure for early 
next week. 


&& 


Near term /through tonight/... 
clear skies dominate the region early this morning and will persist 
through sunrise. The southern fringe of the stratus shield moving 
through southeast North Carolina will meander south over the next 
several hours. The clouds should generally scour out as they move 
farther south and encounter a stronger a more downslope dominated 
environment...but a few may brush the far northern parts of the 
Charleston and Berkeley counties prior to sunrise. Lows are on 
target to bottom out in the 40-45 degree range except slightly 
warmer at the coast. 


The pesky upper low spinning off the virgina Tidewater and northern 
Outer Banks will wobble slowly south/southeast this morning 
before finally turning out to sea as a potent shortwave rotates 
around its western and southern peripheries. The low will have 
little direct impact on the region today with dry conditions 
prevailing area wide. 500mb remain rather cold for middle-March with 
values running -14 to -17c. This will once again support a rather 
thick but shallow cumulus field by late morning which will 
obviously fight the downslope trajectories are are in place. All- 
in-all expect sunny skies to give way to partly to mostly cloudy 
skies. There should still be plenty of sun to help boost highs 
into the middle-upper 60s except along the beaches were cooler 
temperatures will be found. There are certainly indications that a 
very weak sea breeze may try and form as wind fields go light this 
afternoon...especially along the north Georgia coast. 


&& 


Short term /Wednesday through Friday/... 
upper ridge will shift offshore by daybreak Wednesday while a deepening 
southern stream upper trough shifts east-northeast from the Gulf Coast. 
Several shortwaves rounding the base of the larger trough will 
swing through GA/FL...then shift NE into the Carolinas. This will 
aid surface cyclogenesis off the Georgia/SC coast late Wednesday into Wednesday night. 


The NAM and NOGAPS remain the most dry in terms of producing 
precipitation for much of the chs County warning forecast area while the GFS and sref are a bit 
more bullish in bringing precipitation to the area...particularly north of 
the Savannah River. Between Georgia and SC...southeast Georgia has the better shot 
at seeing precipitation so have nudged probability of precipitation into the low-end likely range 
since Georgia will be in closest proximity to the developing surface 
reflection...will have the deepest moisture and will have better 
Omega lift aligned with the moisture. That said...a few of the 
shortwaves swinging into southeast SC will ride along with deeper swaths 
of moisture. The question becomes...can this be enough to overcome 
the deeper dry air seen on WV imagery in response to the weak 
inland high pressure ridge. Have opted to raise probability of precipitation into the middle-high 
chance range for mainly the afternoon hours tmrw...but qpfs will not be 
more than a few hundredths of an inch of rain. 


The surface low will develop further in the Atlantic waters Wednesday night into 
Thursday while the upper low shifts to the coast. As the surface low moves 
further into the Atlantic...this will bring the deeper moisture and 
hence precipitation chances with it into the Atlantic. Have dropped probability of precipitation back 
into the slight to low-end chance range for tmrw night. 


The upper low will then shift offshore during the day Thursday...being 
replaced by an upper ridge moving in from the west Thursday night into 
Friday. If any areas see lingering precipitation early in the day on 
Thursday...it will be the coastal waters as it appears the stacked 
system will be too far offshore and will have to overcome too much 
incoming drier air to produce precipitation over land. Skies will 
continue to gradually clear out Thursday night into Friday as the coastal 
low moves away and upper ridging moves in from the west. 


Temperatures will be undergoing a gradual warming trend Wednesday 
through Friday. Highs will rise from around 60 on Wednesday to the middle 
60s on Thursday...then reaching near to slightly above normal values in 
the low 70s on Friday. Lows will remain in the low 40s away from the 
coast and middle-upper 40s near the shores. 


&& 


Long term /Friday night through Tuesday/... 
high pressure at the surface and aloft will control the pattern 
Friday night into Saturday...bringing a period of warm and dry 
weather to the region. High temperatures could reach the low 70s 
over the weekend...especially considering solid southerly flow 
setting up ahead of the next frontal system far to the west. 


GFS and European model (ecmwf) model solutions diverge fairly significantly Sunday 
into Tuesday. European model (ecmwf) remains the faster model regarding frontal 
progression on Sunday afternoon...while the GFS delays 
precipitation until Sunday night. The slower GFS solution is also 
drier...as it keeps the main upper level energy much further north 
of the forecast area. 


Due to this uncertainty...have capped rain chances at 30 percent 
for Sunday until better model agreement. Even more model 
discrepancy is evident following frontal passage late Sunday 
through Monday...as the GFS aggressively develops a southern stream 
shortwave across the Gulf Coast that spins up another coastal low 
on Monday. This solution would support continued rain chances into 
early next week. 12z European model (ecmwf) shows a weaker shortwave and much drier 
conditions Monday into Tuesday. Prefer to keep rain chances below 
15 percent after Sunday due to this model discrepancy. 


&& 


Aviation /19z Tuesday through Sunday/... 
have VFR conditions prevailing through the 18z taf period for kchs 
and ksav. Expect some VFR stratocumulus to advect across the area 
today resulting in periods of broken skies this 
afternoon...especially for kchs. Overnight and into Wednesday 
morning...high to middle clouds will build into the area as a low 
pressure system approaches from the southwest. Could see some MVFR 
ceilings late in the taf period...mainly for ksav. But will exclude 
any mention of MVFR conditions/rain associated with low pressure as 
best potential remains after 18z Wednesday. 


Extended aviation outlook...there is a chance of MVFR conditions 
in isolated showers Wednesday into Thursday. VFR conditions are then expected 
to return by Friday. 


&& 


Marine... 
high pressure will remain the dominant weather feature over the 
waters tonight. No significant marine issues are expected...with 
winds and seas remaining below small craft thresholds. 


A weak wave of low pressure will move through the region 
Wednesday into Thursday. High pressure will then build back into 
the area Friday through Saturday. Lacking any strong cold 
advection or enhanced gradients...do not expect any marine 
issues through the period...with winds and seas remaining below 
small craft thresholds. 


&& 


Equipment... 
the kclx radar has been down due a wideband connection failure 
since early this morning. Multiple attempts to reconnect the 
wideband line have failed. The kclx radar remains out of service 
until further notice with no estimated time for return to service. 
Further radar updates can be found by the radar free text 
message product issued under WMO header /nous62 kchs/ and AWIPS 
header /ftmclx/. 


&& 


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


&& 


$$ 


Jrj/jpc 

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