933 
fxus66 kmtr 081210 
afdmtr 


Area forecast discussion 
National Weather Service San Francisco Bay area California 
410 am PST Thursday Jan 8 2009 


Discussion...as of 3:28 am PST Thursday...satellite imagery shows 
low clouds across the entire North Bay as well as most of the San 
Francisco Bay area including the Santa Clara Valley. Skies are 
mostly clear for now over Monterey and San Benito counties. The 
approaching cold front is now moving onshore across coastal Oregon... 
and appears to be weakening along the southern fringes. Kbhx radar 
shows weak echoes just moving onshore into eureka's area. Latest 
model guidance has trimmed back precipitation chances for our area for today 
and limit them to only the North Bay...thus have lowered them to 
chance across the North Bay but left the slight chance probability of precipitation intact 
through the greater Bay area as well as the Monterey coast. Latest 
quantitative precipitation forecast estimates give up to around a quarter inch to the higher terrain 
of the North Bay...but only a few hundredths elsewhere. 


Northerly winds are expected to increase behind the front by tonight 
mainly in the hills as strong high pressure builds into the Great 
Basin and a surface trough sets up along the coast. A strong upper 
level high pressure ridge will then quickly build over California 
Friday through the weekend and into next week for warm and dry 
conditions. Warmest areas are expected to be those across the 
southern third of the district...namely interior sections of Monterey 
County as well as San Benito County where 70s will be widespread. 
Temperatures across the Bay area northward will depend upon whether 
or not the Tule fog will persist in the Central Valley. If the fog 
stays then temperatures will be much cooler across the east and North Bay 
valleys as offshore flow advects fog and clammy temperatures into the Bay 
area. 


The forecast still looks dry through the next week and beyond. The 
06z run of the GFS brings a strong...moist trough just off the West 
Coast by the 240 time frame...which is 10 days out. The 00z European model (ecmwf) 
still features a large ridge over the West Coast during this time 
frame...which is probably the more likely scenario. 


&& 


Aviation...as of 4:10 am PST Thursday...low level moisture 
will maintain cloudy conditions across the Bay area including the 
north and East Bay regions and the Santa Clara Valley until midday. 
However conditions remain VFR with ceilings hovering around 600-800 
feet with the exception being ksts which has vlifr ceilings of 100 feet. 
Visibilities have lowered to 3-5 sm across the Bay area with lower visibilities 
over ksts. Temporary ceilings are anticipated over kmry around sunrise 
this morning. A weak frontal system that is approaching the region is 
quickly dissipate. A slight chance of a shower is possible near 
ksts but is not expected any further S. High pressure will build 
in behind the dissipating front ushering in a drier airmass and 
clearer skies by this afternoon. 


&& 


Mtr watches/warnings/advisories... 
... Coastal waters. 




&& 


$$ 


Public forecast: ssa 
aviation/marine: CW 


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