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fxus66 kmtr 062055 
afdmtr 


Area forecast discussion 
National Weather Service San Francisco Bay area California 
155 PM PDT Sat Sep 6 2008 


Discussion...as of 1:50 PM PDT Saturday...conditions early this 
afternoon are nearly identical to yesterday afternoon with warm 
temperatures at the coast and hot temperatures inland. Record high temperatures 
are possible in a few spots...but unlikely in most areas as records 
are generally pretty high for this date. 


Tomorrow still looks to be the transition day as we finally begin 
to cool off. A weak upper level trough currently dropping south 
along the Washington coast is forecast to sag into northern California late 
tonight and Sunday. As it does so...there will be some slight 
airmass cooling. But more importantly for our forecast...the 
approaching trough will trigger a return to onshore flow. 
Temperatures should cool from 7 to 15 degrees near the coast and 
bays on Sunday...and in some of the coastal valleys as well. The 
marine layer will remain quite shallow through Sunday and so cooling 
in the hills and the valleys farthest inland will probably be 
limited to only a few degrees. 


The Big Sur coast is the only area that has seen fog today and recent 
satellite trends indicate the fog layer there is retreating to the 
south. Fog and low clouds will develop along our entire coastline 
sometime in the next 24-36 hours...but pinpointing the timing of 
this isn't easy. The 18z NAM indicates most coastal fog development 
will hold off until late Sunday afternoon/Sunday evening. The high 
resolution WRF indicates patchy fog developing on the North Bay coast 
late tonight...and then becoming more widespread through the day on 
Sunday. Will forecast only patchy coastal low clouds and fog 
tonight...with much more widespread coverage Sunday night into Monday 
morning. 


The cooling trend will spread farther inland Monday and Tuesday as 
the upper level trough deepens along the West Coast. By Tuesday... 
most areas should see temperatures return to near normal. No big 
changes are then anticipated through the remainder of next week as a 
week trough lingers near the West Coast. By late in the week the 
medium range models develop a closed low somewhere near the central 
or Southern California coast. Earlier model runs of both the GFS and European model (ecmwf) 
had indicated that circulation around this low would draw significant 
middle/upper level subtropical moisture up over our region late in the 
week and into next weekend. However...the 12z version of both models 
agree that nearly all moisture will remain well to our east. 
Therefore...have decided to leave probability of precipitation at zero through the extended. 


&& 


Aviation...as of 10:50 am PDT Saturday...high pressure with 
associated subsidence aloft maintaining ceiling and visibility unlimited conditions across the 
central coast and S.F.Bay area terminals. Light onshore pressure 
gradients enhanced by intense interior heating to push afternoon 
breezes at ksfo after 22z westerly 18g25kts but diminishing after 03z 
this evening. Stratus field expected to enhance along the Monterey 
coast and build north overnight so have introduced some low 
overcast and IFR ceilings around kmry and ksns terminals after 10z. 


&& 




Mtr watches/warnings/advisories... 
... Bay evening hours. 


$$ 


Public forecast: dykema 
aviation/marine: Gudgel 




National Weather Service on the web at weather.Gov/sanfrancisco