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Area forecast discussion 
National Weather Service Sacramento California 
900 am PDT Friday Jul 18 2008 


Discussion... 
satellite shows a strong upper ridge over norcal...a weak upper 
level disturbance over southern Oregon and a weak trough approaching 
140w. Tropical Storm Elida is heading west along 20n and the 
monsoon moisture is being shunted east into the 4-corners states. The 
Sacramento area cooled into the 50s this morning as the onshore 
gradient ramped up overnight...stratus clouds are still socking in 
the Vallejo area. The Medford to Redding north gradient of 
6mb...the result of surface high pressure over southern Oregon...is 
bringing light north winds above inversions this morning. These 
will dissipate by afternoon as the surface thermal trough over the 
elevated heat source of the Great Basin strengthens. Expect light 
winds most of the day as smoke continues to plague the northern SAC 
valley to Chico/Marysville/Yuba City...along with Chester and 
Quincy. We should see light upvalley winds with improving 
visibilities and temperatures a few degrees warmer than yesterday by 
afternoon. 


NAM-12 suggests the thermal trough is stronger over the Central Valley 
tonight and WRF again ramps up the onshore gradient 
tonight...bringing another beautifully cool night to the Sacramento 
and Delta areas. GFS/NAM-12 develop a trough along the northern 
California coast tonight...split it and have the southern portion of 
the low about 300 miles west of San Francisco Sunday afternoon. The 
European model (ecmwf) has this a bit closer to the coast...as do several of the GFS 
ensemble members. The Canadian joins most operational models in 
keeping the threat of thunder out of our area. Will continue to 
monitor... 


Snow grains 


&& 


Aviation...high pressure will remain over northern California 
through the next 24 hours...with relatively light winds aloft today 
transitioning to southwesterly overnight. VFR conditions will 
continue to prevail. However...smoke and haze will continue to 
linger over the northern California...primarily from Marysville 
northward or from around Highway 20 northward. Therefore...areas of 
MVFR/IFR will continue to be possible in the vicinity of the fires 
as well as the northern and central Sacramento Valley and the 
surrounding foothills. 


&& 


Sto watches/warnings/advisories...none. 


&& 


$$