Swell Matrix

Area Forecast Discussion

National Weather Service San Francisco Bay Area

1052 am PDT Sat aug 19 2017


A few degrees of cooling are expected over the weekend and into early next week as an approaching trough of low pressure weakens the area of high pressure currently over the Eastern Pacific. Coastal areas will see little in the way of change with continue night and morning low clouds and patchy fog.


As of 08:09 AM PDT Saturday, Non-operational and experimental GOES-16 visible channels reveal another morning of stratus for much of the San Francisco Bay Area and central Coast. The low clouds even managed to reach parts of the inland East Bay earlier this morning, including Livermore where overcast conditions were observed from 5 am PDT to the present. Satellite also depicts the low clouds pushing well into the Salinas Valley and coming within about 15 miles of the Monterey-San Luis Obispo county line. Most communities that are blanketed with low clouds at this time can expect a gradual transition to mostly clear skies by late morning, though there could be some lingering clouds along the immediate coastline. An upper level low near Point Conception will allow for 2 to 4 degrees of cooling compared to yesterday for interior areas this afternoon as height and thickness values decrease.

No major updates planned for the forecast package this morning. Please refer to the previous discussion section for additional details.


As of 10:45 AM PDT Saturday, Slow eroding of the stratus will continue through late morning and into the early afternoon. All TAF sites are expected to be VFR by 20z. Marine layer is still holding at around 2000 feet at this hour. Anticipate MVFR/IFR cigs to return tonight for most sites. Breezy onshore winds will occasionally become gusty this afternoon.

Vicinity of KSFO, Cigs are starting to lift and scatter out around the terminal, though still not confident on exact clearing time. Breezy to gusty afternoon winds, sustained around 15 kt, with gusts near 20 kt at times. Similar marine layer timing and cigs for tonight.

SFO Bridge Approach, Clearing over bridge may occur around the same time as terminal. Confidence is high with clearing slightly after 18z.

Monterey Bay Terminals, MVFR cigs holding strong over MB terminals. KSNS should clear by 1830z, though this will be monitored. Still anticipate KMRY to clear by 20z, but confidence is still low at this time. Brief afternoon clearing will precede an early return of stratus by early this evening. Light to moderate onshore winds this afternoon.


As of 10:31 AM PDT Saturday, Moderate, occasionally gusty, northwest winds will prevail across the northern outer waters and the San Francisco Bay through tonight as high pressure builds in from the west. Winds decrease for all waters by Sunday evening. Locally steep wind waves will also accompany increasing winds.

Watches, Warnings, Advisories

Today, sca, pt arena to pigeon pt 10-60 nm sca, SF Bay

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