551 FXUS66 KMTR 111148 AFDMTR Area Forecast Discussion National Weather Service San Francisco CA 448 AM PDT Thu Sep 11 2025 ...New AVIATION, MARINE... .KEY MESSAGES... Updated at 201 PM PDT Wed Sep 10 2025 - Unsettled weather continues into Thursday - Drier and slightly warmer weather Friday and Saturday. - Unsettled weather may return to the Bay Area on Sunday. && .SHORT TERM... Issued at 239 AM PDT Thu Sep 11 2025 (Today and tonight) Quick recap - Afternoon/evening precip has diminished. There are a few lingering echoes about 60 miles west over the ocean and near Monterey Bay, but they're fading fast. KMUX has been returned to surveillance/clear air mode. Decent September rainfall amounts recorded over the last 12-18 hours with a trace to nearly three quarters of an inch. One notable rainfall total is San Jose, with 0.41 inches, which sets a new daily record. Today and tonight: We've got one more day of precip chances around the Bay Area. The reason? A double-barrel upper low continues to spin over far NorCal, which is embedded in a positively tilted upper level trough. Model guidance has been rather persistent in keeping precip over the North Bay once again this afternoon. Wednesday there were concerns of excessive rainfall and thunderstorms, but that threat has shifted farther N and E with better dynamics today. So is there a low chance for thunderstorms again this afternoon? SPC brings the day one outlook just to the Napa county line. Further analysis of CAMS reveals some solid instability at the surface and just above the surface. However, lapse rates aloft are meager at best from 700-500mb. Additionally, point soundings show a weak cap/inversion around 650mb depending on your model of choice. Given the positive tilt of a weakening trough don't think that will be enough to tip the scales toward thunder. Therefore, will keep precip mention to showers over the North Bay. There could some build ups over the Diablo and Gabilan ranges, but will not mention precip at this time. Otherwise, satellite fog product overnight shows a psuedo-marine layer or more like strato-cu layer blanketing the Bay Area and Central Coast. This layer will thin by late morning/early afternoon, but given the lift nearby some afternoon clouds will linger. Speaking of the satellite. One can still see a pronounced heat signature from the Garnet Fire in the Sierra. Any precip will diminish by tonight as the low/trough move eastward and weakens further. In its wake subsidence develops with a redeveloping marine layer around 2k feet. && .LONG TERM... Issued at 259 AM PDT Thu Sep 11 2025 (Friday through Wednesday) Warmer and drier conditions develop on Friday and into Saturday thanks to shortwave ridging that develops behind the departing upper low. Night and morning marine layer clouds will return, but compressed slightly. Temperatures return to the 70s and 80s with interior Central Coast reaching the 90s. A little bit of a roller coast temp-wsie as temps dip slightly on Sunday thanks to a passing front to the north. A few showers over the northern coastal waters, but by the time they reach the North Bay they fall apart. Early next week longwave pattern continues to favor ridging over the west with a low/trough Northern Rockies. A few of the ensembleseven show some weak offshore flow around Sept 16. && .AVIATION... (12Z TAFS) Issued at 448 AM PDT Thu Sep 11 2025 MVFR CIGs to continue through late morning. Confidence is moderate in the timing of stratus clearing this morning with with guidance suggesting most sites clearing by 18/19Z. For the Central Coast, clearing times may be more optimistic with some models showing clearing later around the timeframe of 20/21Z. A more typical marine layer pattern will return tonight as the upper level low departs the Bay Area. Current thinking is the marine layer will be around 2000 ft (favoring MVFR CIGs) and overcast conditions will return late overnight. The exception is along the coast (HAF, MRY, SNS) where confidence is moderate to high that stratus will return early in the evening. Vicinity of SFO...MVFR becoming VFR during the afternoon/evening before MVFR conditions return overnight. Ceilings are expected to clear by 19Z but LAMP guidance does suggest clearing could be delayed to 20Z. Onshore winds strengthen during the afternoon/evening with gusts to 21 knots expected. ECMWF ensemble guidance shows some potential for slightly stronger gusts up to 25 knots to develop at SFO today. Confidence in timing of stratus return tonight is low to moderate. Currently thinking stratus will return closer to 09Z but there is some potential for it to return as early as 06Z. SFO Bridge Approach...Similar to SFO. Monterey Bay Terminals...MVFR conditions continue through late morning before a brief period of VFR conditions this afternoon. Highest confidence in stratus clearing by 18/19Z but this may be on the more optimistic side with some ensemble members indicating clearing by 20/21Z. MVFR CIGs return late this afternoon/early this evening with ceilings to gradually lower to IFR overnight. Moderate confidence in timing of transition from MVFR to IFR overnight tonight. && .MARINE... (Today through Tuesday) Issued at 448 AM PDT Thu Sep 11 2025 Northwest winds increase beginning Thursday, becoming moderate to fresh across the majority of the coastal waters. Localized strong gusts are possible across the northern outer waters. Moderate to rough seas develop Friday and persist into next week. Conditions temporarily improve Saturday, as winds decrease and seas ease, before another round of fresh to strong NW winds returns Sunday into next week with the strongest winds located across the far northern outer waters. && .MTR WATCHES/WARNINGS/ADVISORIES... CA...None. PZ...Small Craft Advisory from 3 PM to 9 PM PDT Friday for Mry Bay- Pigeon Pt to Pt Pinos 0-10 nm-SF Bay N of Bay Bridge. Small Craft Advisory from 9 PM this evening to 3 AM PDT Saturday for Pt Arena to Pt Reyes 0-10 nm. Small Craft Advisory from 9 PM this evening to 9 AM PDT Friday for Pt Pinos to Pt Piedras Blancas 0-10 nm. Small Craft Advisory from 3 PM Friday to 3 AM PDT Saturday for Pigeon Pt to Pt Pinos 10-60 NM-Pt Pinos to Pt Piedras Blancas 0-10 nm. Small Craft Advisory from 3 PM this afternoon to 3 AM PDT Saturday for Pt Arena to Pt Reyes 10-60 NM. Small Craft Advisory from 9 PM this evening to 3 AM PDT Friday for Pigeon Pt to Pt Pinos 10-60 NM. && $$ SHORT TERM...MM LONG TERM....MM AVIATION...Kennedy MARINE...Kennedy Visit us at www.weather.gov/sanfrancisco Follow us on Facebook, X, and YouTube at: www.facebook.com/nwsbayarea x.com/nwsbayarea www.youtube.com/nwsbayarea