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Area forecast discussion 
National Weather Service Sacramento California 
900 PM PDT Tuesday Aug 19 2008 


Discussion...weak Pacific frontal system now moving into Pacific 
northwest bringing high and middle cloudiness across the far northern 
County Warning Area at this time. Some light radar echos showing up on mfr radar but 
all well north of the forecast area boundary. A short wave trough 
that moved through norcal this afternoon has moved into Nevada this 
evening so the remainder of the forecast area is under mainly clear 
skies. Temperatures this evening running similar or just a bit 
higher than 24 hours ago after coming in with similar highs to 
mondays. Exception was the Delta and Delta influenced areas where a 
lighter Delta breeze today allowed for several degrees of warming. 
Overnight lows in current forecast package expected to be similar to 
this mornings. Although airmass warms a bit tonight over 
last...lighter winds most areas should allow for temperatures to 
drop a bit more so overnight lows forecast for tonight look okay. 


Upper low now centered near 51n 138w forecast to move towards the 
British Columbia coast on Wednesday. A weak frontal band is still forecast to skim 
far norcal Wednesday night with perhaps a secondary shortwave 
associated with the main low crossing far norcal on Thursday. All of 
these systems still prognosticated to remain too far north to produce 
serious precipitation threat but a few sprinkles across the northern 
mountains Wednesday night still looks okay based on latest evening 
NAM run. Main affect for our forecast area will be to keep daytime 
highs several degrees below season normals. 


Upper ridge begins building over the West Coast on Friday for the 
beginning of a warming trend. This warming trend will last through 
the weekend as high pressure remains over the western U.S. But 
daytime highs still only expected to reach near or few degrees above 
season normals thanks to a continued onshore flow at all levels. 


Late Sunday night into Monday...the GFS and European model (ecmwf) models suggest a 
trough affecting northern California. The two models differ in how 
deep the trough will dig into California but even deeper GFS keeps 
precipitation threat mainly north of County Warning Area. Main effect will be cooling 
trend back to near normal temperatures 


&& 


Aviation...weak frontal system moving through Pacific northwest 
will continue to bring moderate southwesterly flow at the higher 
elevations and through the Delta with scattered middle to high level clouds 
across the far North Sacramento valley. Upper trough should mix out 
the marine layer so minimal or no coastal low clouds are expected to 
affect the Sacramento area terminals tonight. A secondary frontal 
system will skim norcal on Wednesday and Wednesday night bringing 
similar conditions will breezy southwest winds and high to middle 
clouds across the north. 


&& 


Sto watches/warnings/advisories...none. 


&& 


$$