Weather

880 
fxus66 kmtr 080545 
afdmtr 


Area forecast discussion 
National Weather Service San Francisco Bay area California 
900 PM PDT sun Sep 7 2008 


Discussion...as of 9:00 PM PDT Sunday...an upper low is currently 
centered near Redding and the circulation around this feature was 
visible in the clouds and smoke earlier this afternoon and evening. 
The water vapor shows the vorticity maximum circulation as well. The effects 
locally have been to induce the deepening of the marine layer. 
Earlier today the stratus enveloped the entire coast and its now 
starting to spread inland. Clouds are already being reported at 
Oakland and sfo with low cloud decks at mry/sns and wvi with stratus 
quickly filling the Salinas Valley. North of Point Reyes the low 
clouds are filling inland and will likely make it into Santa Rosa 
shortly. The depth of the marine layer is roughly 1000-1500 feet but 
will continue to slowly deepen overnight as the upper atmospheric low 
pressure passes overhead. One last night of mild and dry weather for 
the inland hills above 2000 feet. 


Expect a cloudy start for most areas below 1500 feet on Monday with 
much cooler temperatures for inland areas on Monday. The far inland 
valleys still warmed well into the 90s and triple digits today but 
that wont happen on Monday with the presence of the upper low and 
deepening marine layer. Tomorrow is the type of day where there is 
big temperature bust potential for places like Concord and Livermore. 
The current grids and latest MOS data still suggest temperatures into the 
upper 80s but if the marine deck continues to deepen with brisk 
onshore winds through the day they could have a hard time reaching 
80. In addition the trajectory of the upper low could induce a 
southerly wind flow into the North Bay valleys which is often a 
clammy wind for the locales of Napa and Santa Rosa. 


The latest 00z NAM run keeps the 500 mb trough axis right over 
the Bay area on Monday and Tuesday so cloud decks could be slow to 
clear both around sf Bay and the coastline with periodic drizzle. 
The deepening of the layer should preclude widespread dense fog on 
the roadways and keep it confined to the hillsides. The latest NAM 
then brings a shortwave into the Bay area Tuesday night into 
Wednesday with subtle cool advection that will reinforce the marine 
layer and make any of the recent heat a distant memory. If the 00z 
NAM is a pre-cursor to the incoming 00z GFS and European model (ecmwf) then temperatures will 
average below normal for much of the week with extensive night and 
morning clouds in the valleys. 


After the middle-week cool down a modest upward trend in temperatures 
should occur towards the weekend as the trough ejects eastward. 


&& 


Aviation...as of 10:30 PM PDT Sunday...marine layer expected to 
deepen overnight which will push stratus into all of the sfo Bay 
area. Burnoff times forecast to be 17z at sfo and 18z for the sfo 
approach zone. 


&& 




Mtr watches/warnings/advisories... 
... Bay. 


$$ 


Public forecast: r walbrun 
aviation/marine: west pi 




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