Area Forecast Discussion
Issued by NWS San Francisco Bay Area, CA

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000 FXUS66 KMTR 192026 AFDMTR Area Forecast Discussion National Weather Service San Francisco Bay Area 126 PM PDT Sat Aug 19 2017 .SYNOPSIS...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. && .DISCUSSION...
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as of 1:25 PM PDT Saturday...Today`s stratus has been a bit slower to mix out compared to yesterday. Visible satellite shows clouds along entire coastline from Sonoma County south through Monterey County, and even some clouds pushing through the Golden Gate east into Berkeley. For the next several hours, we have one of the two GOES-16 mesoscale sectors over parts of the PacNW with its southern extent covering the San Francisco Bay Area. With this mesoscale sector, we are able to get detailed satellite imagery once every minute. It`s fascinating to watch this minute-by-minute data with the clouds gradually mixing out over the Bay combined with the continued push through the Golden Gate Gap. Check out @NWSBayArea on Twitter to see it for yourself! Synoptically-speaking an upper level low is centered just over a hundred miles offshore from Los Angeles. This low will help to enhance potential thunderstorm activity over the next few days for parts of southern California as well as the Sierra Nevada. For us along the central coast and for the San Francisco Bay Area, we`re a bit too far north to expect any sort of convective activity. Nonetheless, the low is close enough to bring a gradual cooling trend across interior areas of the San Francisco Bay Area, San Benito County, and interior Monterey County through the weekend. This checks out for today as temperatures for most airports in the area are running a few degrees below what they were 24 hours ago. When all is set and done this afternoon, expect highs to generally reach the 60s along the coast and the middle 70s to low 90s for interior areas. Little change is expected for highs on Sunday along the immediate coast, but an additional 2 to 5 degrees of cooling is likely inland. Minimal day-to-day changes are anticipated for the entire area for much of next week. The cloud cover forecast for Monday continues to be a bit of a challenge. If conditions permit, a partial solar eclipse can be viewed throughout California while the total eclipse can be viewed north in Oregon. Models remain in good agreement that the upper level low will remain parked near Point Conception in southern California. Current thinking is that there will be cloud cover along the coast on Monday morning. The big questions are 1) how far inland will these clouds be, and 2) will areas with morning clouds clear early enough to see the eclipse? We cannot confidently answer these questions quite yet. Another potential outcome (not likely, but still possible) is that the upper low could end up mixing out the marine layer, allowing for mostly clear conditions for much of the area. We will continue to monitor the marine layer`s behavior over the next 48 hours to see how it responds to this upper low. The marine layer depth has trended upward from 1,200 ft to 2,000 ft over the past day. Climatologically- speaking, the best locations in the Bay Area for clear skies on a mid/late August morning would be interior areas of the East Bay away from the coast, as well as the higher elevations in the Santa Cruz Mountains, North Bay Mountains, and Diablo Range. The eclipse of the sun will begin shortly after 9:00 am PDT for the Bay Area with peak obscuration happening around 10:15 am PDT. Peak obscuration of the sun will range from 71 percent in Monterey and up to 78 percent in Santa Rosa.
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&& .AVIATION...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. && .MARINE...
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as of 1:11 PM 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.
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&& .MTR WATCHES/WARNINGS/ADVISORIES...
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.Tngt...SCA...Pt Arena to Pigeon Pt 10-60 nm SCA...SF Bay until 3 AM
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&& $$ PUBLIC FORECAST: Rowe AVIATION: BAM MARINE: BAM Visit us at www.weather.gov/sanfrancisco Follow us on Facebook, twitter, and youtube at: www.Facebook.com/nwsbayarea www.twitter.com/nwsbayarea www.youtube.com/nwsbayarea

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