Issued at 842 PM PST Mon Dec 15 2025
The picture from space shows some high clouds passing over the region, with some pockets of stratus and fog peaking through for the East Bay valleys. For the first time in three days, the evening update does not include a Dense Fog Advisory! This may be short lived as visibility has started to drop in the North and East Bay valleys this evening, but for now, if you're traveling this evening, be prepared for patchy fog in these areas. Given how foggy it's been the past few mornings, consider checking the forecast, weather, and traffic conditions before heading out tomorrow.
, Issued at 104 PM PST Mon Dec 15 2025 (This evening through Tuesday)
Interesting setup this afternoon weather wise. No real change for the Central Valley or interior East Bay as they still deal with Tule Fog impacts. North Bay, SF Bay, and the South Bay on the other hand are seeing a welcomed sight, the Sun. Some of these locales struggled to see the Sun over the weekend keeping them chilly. That being said, even with some sunshine this afternoon it's late in the day and not much daytime heating left. Therefore undershot the forecast from the NBM today for most of the Bay Area, especially the interior East Bay. Central Coast will be the warmest of the bunch with a few spots aiming for the lower 70s.
So why the change? Lingering offshore flow over the North and East Bay combined with a weak system approaching from the north. Latest surface analysis shows a weak cold front off the far NorCal coast moving S and E. In fact, KMUX radar was switched to precip for the first time in a long time. A few scout showers ahead of the front are being picked off the North Bay coast this afternoon.
For tonight: do have showers returning to the North Bay overnight. Not expecting a big precip event tonight, but more of a brush by from a passing boundary. Current forecast doesn't have precip south of the Golden Gate. If we do actually get some bucket tips from rain this will be the first precip of the month for the region. In other words, it's been dry lately. One impact that won't go away tonight will be low clouds and fog, especially East Bay and West Delta. Given the approaching front and increased cloud cover not expecting widespread dense fog like this morning, but patchy dense fog is more likely.
For Tuesday; Showers finally make it south of the Golden Gate by the afternoon with minor impacts to the evening commute. Once again, not expecting a wash out, but beneficial precip nonetheless.
..issued at 202 PM PST Mon Dec 15 2025 (Tuesday night through next Sunday)
Showers will linger through Wednesday as the weak boundary traverses the region. Showers will be most prevalent across the North Bay. Rainfall amounts with this first push of precip will generally be a tenth to a half for the North Bay and a few hundredths elsewhere. Interior areas of the Central Coast will likely not see any precip with this system.
We'll get a brief pause/break in widespread precip late Wednesday evening and Thursday before the atmosphere reloads with another system. If there are a few lingering showers they'll be across the North Bay.
The atmospheric "reload" will come in the way of a low spinning up over the Pacific north of HI and another storm system swinging into the PacNW. This set up will allow for a moisture plume to take aim at the PacNW before sliding down the NorCal coast on Friday. Widespread rain returns initially to the North Bay Friday afternoon before pushing south to the Central Coast on Saturday.
By Sunday the newly formed low over the Pacific will move toward the NorCal, which will bring a reinforcing shot of higher PWAT air to the region. As a result, expect another uptick in rain shower activity, coverage, and intensity. This push of moisture will keep precip in the picture Monday and even into Tuesday. A great way to describe the overall weather starting Friday through early next week will be episodes or periods of rain. Not a complete washout, but measurable rain. Initial rainfall projections Thursday through Monday: North Bay and Coastal Mts 2-5", Bay Area and Monterey Bay Region 1-2", Interior Central Coast less than 1". Period of heaviest rainfall looks to be Sunday into Monday.
Lots of focus for the extended, and rightfully so as holiday travel and holiday plans come into play. Confidence continues to increase that impactful weather will return to the region beginning around Dec 22 and continuing through the holiday. CPC continues to highlight a large portion of NorCal for excessive rainfall. Longer range ensembles show potential as well, but this far out it's all about the details - amounts, confidence, timing, impacts. Those will be sorted out in the days to come. Please check back for updates and more details.
(06z TAFS) Issued at 930 PM PST Mon Dec 15 2025
Generally VFR across the region with some high level clouds, barring SNS where radiatively forced visibility reductions have begun, and the interior eastern Bay Area and the vicinity of APC where the Tule Fog has grown over CCR, but not LVK. With the lack of stratus and fog development so far tonight, have pulled back stratus formation times across the region. Lowest confidence for stratus formation at the Monterey Bay terminals where there is a good chance both MRY and SNS remain VFR overnight. Will continue to monitor stratus development through the night. Expected arrival of high cloud cover on Tuesday makes the clearing times uncertain, and opted to generally retain the previous forecast. Light to gentle onshore breezes develop on Tuesday with light rain showers developing in the North Bay, spreading southwards in the evening hours.
Vicinity of SFO, VFR with mid- to high level clouds at present. Latest model output has delayed the onset of MVFR ceilings to around the 12-13Z timeframe, but have opted to push the onset to 09Z to account for any interaction between coastal stratus and Tule Fog impacts. Low confidence that dense fog directly impacts the terminal, but some reduction in visibility is expected overnight. Afterwards, moderate confidence that the stratus persists through the rest of the TAF period. Winds will remain light to gentle throughout the forecast period, with west-northwest flow developing by Tuesday. Low to moderate confidence of showers developing at the terminal by Tuesday evening.
SFO Bridge Approach, Localized stratus and potential for dense fog is expected tonight through Tuesday morning across the southern San Francisco Bay. Otherwise, similar to SFO.
Monterey Bay Terminals, Confidence in the return of stratus tonight has decreased remarkably as the stratus deck remains well off the coast. Have converted the LIFR stratus and fog forecasts to TEMPO groups as a result, and going by the latest model output, even that might be overly pessimistic. Greater confidence in stratus returning to the region Tuesday evening as the stratus deck inches onshore. Light drainage flows continues overnight before light to gentle northwest winds resume on Tuesday afternoon.
(tonight through next Sunday) Issued at 842 PM PST Mon Dec 15 2025
Southerly flow will prevail north of Pigeon Point ahead of an approaching frontal system. Moderate to fresh winds continue across the southern waters with periods of moderate winds expected across the northern waters. Patchy dense fog persists within the West Delta, and expands across the Bays and the coastal waters tonight into Tuesday morning. A weak system will bring moderate long period northwest swell Tuesday into the weekend. Moderate seas return with wave heights building up to 9 feet. Rain chances increase late tonight and remain elevated through the end of the forecast period.
Ca, None. PZ, Small Craft Advisory until 9 PM PST Tuesday for Pt Pinos to Pt Piedras Blancas 0-10 nm.
