, Issued at 346 PM PST Sat Dec 20 2025 (This evening through Sunday)
The atmospheric river moisture plume continues to oscillate this afternoon, the focus has been on the Bay Area since mid-morning and will then gradually move back toward the North Bay tonight into early tomorrow morning. After sunrise Sunday, we'll see a notable shift south toward the Central Coast as the upper level trough associated with the strengthening system in the Gulf of Alaska deepens. The twenty-four hour rainfall totals in the North Bay are ahead of pace, with the Flood Watch beginning this afternoon and periods of moderate to heavy rainfall expected overnight within the area covered by the watch.
Satellite imagery this afternoon shows a large cloud shield extending from Monterey Bay well north into southern Oregon. The combination of a surface trough shifting south from NorCal to the Santa Cruz mountains by late Sunday, a fully saturated boundary layer up to 850mb and continuous shortwave energy embedded in the 500mb flow will result in rainfall totals across the North Bay around 2-3" in the valleys and other low-lying areas, with higher elevations potentially seeing up to 6" or more locally. The Mark West Creek Near Mirabel Heights is forecast to reach action stage by late Sunday evening, travelers should be cautious driving through through the North Bay for the remainder of the extended forecast.
..issued at 346 PM PST Sat Dec 20 2025 (Sunday night through next Friday)
Monday offers a bit of a reprieve for the North Bay as the atmospheric river moisture plume is once again pushed south toward the Santa Cruz Mountains and the remainder of the Central Coast. The deepening and expanding upper low moving south out of the Gulf of Alaska begins to assert its influence over the synoptic pattern at our latitude. As the atmosphere resets to the west over open water we'll still see scattered light rain across most of our area during the day Monday with minimal impacts.
By Tuesday, some uncertainty is introduced into the forecast. The most recent guidance suggest a less dynamic surface response to the deepening trough offcoast, especially early on. Previous guidance indicated rapid surface pressure falls during the day Tuesday, with the strong area of low pressure taking aim at the Bay Area/North Bay by late Tuesday night. Tuesday into Wednesday is now in the later time frame of higher resolution data as well, with the NAM12 indicating a less organized response at the surface over that same time frame as well. Deterministic guidance depicts a more organized surface response later in the forecast period and farther north off the coast of NorCal by late Wednesday night. The differences are somewhat subtle and confidence for impactful rainfall across the North Bay between now and the end of the week remains very high.
For the most part all the ensemble members have begun to pick up on the subtle changes in the surface response and pattern. While some of the inland rainfall totals may come down somewhat as we move through the week, the pattern remains wet throughout our entire forecast area and travel impacts will persist, especially the farther north you are. Storm force to near hurricane force winds at times up and down our coast Tuesday through early Friday will continue to produce exceptionally dangerous conditions along our coastal beaches and coastal waters.
(18z TAFS) Issued at 951 AM PST Sat Dec 20 2025
Fog and low clouds continue to plague the North Bay terminals this morning, with LIFR conditions prevailing, despite rain starting to fill in across the region. Elsewhere, MVFR conditions will continue to persist, but may temporary drops to IFR and LIFR CIGs are possible through late this morning. Guidance continues to favor IFR CIGs, but CIGs are currently ranging between IFR and MVFR. Similarly, guidance is showing more significant drops in visibility while obs show it remaining largely stable so far. Thinking is that visibility will initially remain more stable but decrease as more persistent moderate showers arrive this afternoon/tonight. Winds strengthen towards the end of the TAF period with gusts in excess of 20 to 25 knots possible along the coast, North Bay, and SF Bay Shoreline.
Vicinity of SFO, Light showers are moving through the Bay Area with ceiling heights fluctuating between MVFR and VFR. Moderate confidence that MVFR CIGs will generally prevail through the afternoon as the rain fills in across the region today. SFO is currently on the southern edge of the rain band, so if it sags southward through the day, think there is a good change (60%) of MVFR CIGS and rain prevailing through the day. Winds strengthen by mid to late tomorrow morning with gusts between 25 to 30 knots likely.
SFO Bridge Approach, Similar to SFO.
Monterey Bay Terminals, CIGs remain on the IFR-MVFR border with light offshore winds continuing. Showers are developing in the vicinity of MRY and SNS over the Monterey Bay, but they are not expected to cause any major impacts today. Rain showers become more widespread tonight into tomorrow morning, with light to moderate rain reaching both terminals by 08/09Z tomorrow. Generally expecting overcast conditions to persist for much of today, but may see some clearing at SNS during the afternoon.
(today through Thursday) Issued at 918 AM PST Sat Dec 20 2025
Wet and unsettled weather to prevail through Tuesday, with increasing coverage in the showers activity today. Rain intensity increases over the northern waters by Sunday. Winds remain light and southerly through tonight when winds strengthen to fresh to locally strong ahead of cold frontal passage Sunday into Monday. Winds diminish early Monday before restrengthening late Tuesday as a more substantial, stronger system arrives Tuesday into Wednesday. This system will bring widespread gale force to near gale force winds and the potential for isolated hurricane force gusts across the interior coastal waters from Point Sur to Point Pinos. Seas build through the second half of next week, becoming very hazardous for mariners with the potential for wave heights in excess of 20 feet.
Ca, Flood Watch through Monday afternoon for CAZ502>506.
PZ, Small Craft Advisory from 9 PM this evening to 9 PM PST Sunday for Pt Arena to Pt Reyes 0-10 nm-Pt Arena to Pt Reyes 10-60 NM-Pt Reyes to Pigeon Pt 0-10 nm-SF Bay N of Bay Bridge.
Small Craft Advisory from 9 AM to 9 PM PST Sunday for Mry Bay-Pt Pinos to Pt Piedras Blancas 0-10 nm.
Small Craft Advisory from 3 AM to 9 PM PST Sunday for Pigeon Pt to Pt Pinos 0-10 nm-Pigeon Pt to Pt Pinos 10-60 NM.
