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Area forecast discussion 
National Weather Service Sacramento California 
830 PM PST Wednesday Nov 19 2008 


Discussion... 
upper level trough approaching the West Coast today bringing a 
cooler air mass to interior northern California. Temperatures were 5 
to 10 degrees cooler today compared to yesterday in most locations. 
Some high clouds across the area tonight may keep patchy fog forming 
north of Sacramento but may still form Sacramento southward. Low 
clouds from the Bay area into Vallejo this evening and will move 
into the Delta Region and possibly into the valley overnight with 
onshore flow. The fog should improve by 10 am but low clouds may 
stick around into the afternoon. 


The upper level trough moves into the Pacific northwest tomorrow 
brushing northern California. The trough will bring more clouds and 
cooler temperatures along with a slight chance of precipitation to 
the northern mountains and possibly the northern Sacramento Valley 
on Thursday. Any precipitation is expected to be light (less than a 
tenth of an inch in the most locations in the mountains). Snow 
levels expected to be around 6500 to 7500 feet but little to no 
accumulation is expected. Weak ridging builds in behind the trough 
diminishing the showers by Thursday evening. Surface high pressure 
builds into Oregon creating a mfr-SAC surface pressure gradient of 5 
mb Thursday evening and 8 mb by Friday morning. This will bring 
locally gusty north to northeast winds tomorrow night into Friday 
morning. Weak ridging on Friday bringing a little warmer 
temperatures. Another weak system moves through Saturday morning 
bringing a few clouds to the north. Although any precipitation is 
expected to stay northwest of interior northern California. 
Weak ridging on Sunday for dry weather and near normal temperatures. 


Another trough is expected to approach the West Coast early next 
week. Although the models differ with solutions so confidence is low 
in the timing and track of the trough or a possible development of 
closed low. The 00z GFS shows the closed low developing over the 
eastern Pacific on Sunday night into Monday and brings it off the 
Southern California coast on Tuesday. The ensemble mean GFS shows a 
trough moving through that is weaker than the European model (ecmwf). The 12z European model (ecmwf) 
show a weak trough moving through the Pacific northwest brushing 
northern California on Monday and another trough off the northern 
California on Tuesday forming two closed lows moving inland on 
Wednesday. Either way it looks like we should have near to below 
normal temperatures and periods with a threat of precipitation for 
the first part of next week. 


&& 


Aviation... 
general VFR conditions with periods of middle and high clouds. Lower 
clouds and light precipitation possible over the northern mountains 
tomorrow with the trough moving through. Low clouds in the Bay area 
tonight will spread into the Delta Region and possibly into Sacramento 
overnight with onshore flow. Patchy fog and low may develop in the 
Sacramento area bringing areas of MVFR/IFR conditions tonight into 
Thursday morning. Patchy fog may develop around ksck overnight into 
Thursday morning with areas of MVFR and local IFR and isolated LIFR 
conditions. Southwest winds gusts up to 40 miles per hour over the mountains 
with the approaching cold front Thursday. 


&& 


Sto watches/warnings/advisories...none. 


$$