Area forecast discussion 
National Weather Service San Francisco Bay area 
459 PM PDT Fri Oct 21 2016 

Synopsis...temperatures will cool off to closer to normal by 
this weekend as high pressure currently over the West Coast moves 
to the east. An unsettled weather pattern is expected to develop 
early next week with rain chances on Monday and Tuesday and then 
again late in the week. 

&& of 3:00 PM PDT Friday...mostly sunny conditions 
across our County Warning Area today although over the past few hours clouds have 
been advancing back to the immediate coastline. Temperatures have 
generally been running just under values from Thursday except 
around Monterey Bay where a more pronounced sea breeze has values 
up to 20 degrees cooler than yesterday. 

Additional cooling can be expected over the weekend as 500 mb 
heights continue to lower as the ridge axis shifts farther to the 
east. A longwave trough will head toward the West Coast with the 
potential for some light drizzle ahead of it to get into the 
North Bay Sunday afternoon or evening. For other spots the only 
impact will be to keep highs in the 60s to mid 70s. 

By Monday an upper level low will advance to just west of the 
British Columbia/Washington coastline while an associated frontal system moves down the 
coast. Rain will likely get into the San Francisco Bay region 
Monday night and possibly into portions of Monterey Bay going into 
Tuesday. Precipitable water values are forecast to be 1 to 1.15" which is 
considerably less than the values from the past couple of systems. 
Rainfall amounts will range from locally more than 1" over the 
North Bay to 1/10" to 1/3" around sf Bay. Locations south of Santa 
Cruz will probably see little to no rainfall. Highs will be in the 
60s to lower 70s. 

After a break in the rain, models have been showing the potential 
for another system to bring rainfall back to our region. 
Disagreement between the various solutions as far as timing and 
location of the main moisture plume (pw values over 1.30") makes 
it difficult to provide much specificity for Thursday into 
Saturday. For now will go with chance pops for the entire period 
until better agreement is reached. CPC does continue to highlight 
above normal rainfall for Thursday of next week through most of 
the following week with the highest likelihood for Monterey 
County southward. 

&& of 4:58 PM PDT Friday...patchy IFR cigs are 
reported along the immediate coast, VFR elsewhere. Onshore winds 
are mainly light though locally gusty nearest the San Francisco 
Bay. Sfo-SAC pressure gradient is light at 1 mb and the acv-sfo 
gradient is near 5 mb, but the northerly gradient is forecast to 
weaken through tonight and Saturday then reverse to a southerly 
direction late Saturday. Generally looking at light winds with 
high pressure aloft steadily weakening through the period. 

Vicinity of ksfo...VFR. Westerly wind gusts to 20-26 kt til 04z 
then diminishing. Tempo IFR cig possible around sunrise tomorrow. 

Sfo bridge approach...similar to ksfo. 

Monterey Bay terminals...patchy IFR developing this evening, areas 
of IFR tonight and Saturday morning. Clearing returns by late Saturday 

&& of 10:55 am PDT Friday...moderate northwest winds 
will continue today ahead of an approaching trough. The strongest 
winds will be around Point Reyes and Point Sur. Winds will 
gradually ease through the weekend as low pressure descends into 
the region. This low pressure will bring a longer period 
northwest swell to the area. 


Mtr watches/warnings/advisories... 
... Pt to pt pinos 0-10 nm 
Small Craft pinos to pt Piedras Blancas 0-10 nm 
Small Craft Arena to pt Reyes 0-10 nm 
Small Craft Arena to Pigeon pt 10-60 nm 
Small Craft Advisory...Pigeon pt to pt Piedras Blancas 10-60 nm until 9 PM 
Small Craft Reyes to Pigeon pt 0-10 nm until 3 am 



Public forecast: Bell 
aviation: canepa 
marine: drp 

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