textproduct: San Francisco Bay Area

KEY MESSAGES

Updated at 432 AM PST Tue Dec 30 2025

- Cold morning conditions for interior and valley locations again this morning.

- Rain returns Wednesday, becomes widespread for New Years Eve, and additional rains expected over the weekend and into the next work week.

- Coastal flooding from King Tides is expected Wednesday through Sunday.

SHORT TERM

Issued at 432 AM PST Tue Dec 30 2025 (Today and tonight)

Another mostly quiet night so far, with the cooler and dry airmass allowing for temperatures to fall into the mid 30s for the more interior areas. Cold Weather Advisories are in effect for these areas, and Dense Fog Advisories are also in effect for the North and East Bay valleys. The overnight forecast package had a focus on the cool overnight lows and the intrusion of fog from the Sacramento Valley. Additional adjustments were made to winds as well to better capture some of the increases in gusts during the offshore flow as well as the mid week pattern change.

Today's weather continues the trend of a cold morning followed by mostly clear conditions into the afternoon and highs peaking again in the 50s and 60s. Though, the late afternoon will show signs of the upcoming pattern change, as high clouds build from the south. These clouds will fill over the region as the large cut-off low to the southwest re-enters the jet stream and makes its way toward the California coast.

The orientation of this low relative to us will allow warmer and more moist air to work its way up from the south. This will have most areas seeing overnight temps plateauing in the 40s and prevent another round of Cold Weather Advisories. Then the first wave of rain arrives to the southern counties early Wednesday.

LONG TERM

Issued at 432 AM PST Tue Dec 30 2025 (Wednesday through Monday)

Models have been locked in on this cut-off low providing the California coast with another round of rain for a while, but timing and overall rain amounts had been harder to narrow down. The more recent updates and the inclusion of shorter-term, higher resolution models have lead to a better consensus. However, there still seems to be some struggles in model guidance on the finer details, possibly from how uncommon of a set up our next rainmaker will be.

It's interesting to watch, as it is already in motion: Our current ridging pattern and trough to the west has begun transporting a cut- off low northward from around the 30th parallel. This southerly pull of moisture wouldn't be out of place in months like August, but it's fairly rare mid-winter. What will this mean? Quite a bit of rain for SoCal, while light to moderate rain builds into the Central Coast early on the 31st and becoming CWA-wide as we welcome in the New Year.

The low will push inland through the second day of the new year as it gets folded into the building trough ahead of the next, more classic, winter rain system arriving into the end of the week. The time of arrival for the this system could still be delayed, but the current forecast shows a cold front arriving along the coast this Friday with it's parent low building in close behind into that weekend. This looks to offer higher rain rates and much stronger winds than the cut-off low, but does look to move through the area at a good pace, preventing chances for elevated rain rates from staying over one area for too long.

Model agreements splinter through the late weekend and into the next work week, but the ECMWF and GFS outputs do call for a wet January. The big differences between the two are more down to the timing and the paths these systems take, but they are both calling for the jet stream to become a conveyer belt of cold fronts and low pressures moving through the area. This won't leave a lot of time between rain systems and could lead to more of a marathon of rain chances. This will be something worth checking back in on as the forecast evolves.

AVIATION

(12Z TAFS) Issued at 432 AM PST Tue Dec 30 2025

Tule fog has seeped into portions of the east bay and is trying to spread through some of the valleys. This has dropped visibility around Byron and Concord but has yet to infiltrate LVK yet, though it is flirting with APC. Opted to trend slightly more pessimistic with APC and hinted at the possibility of reduced cig and vis for LVK. To the north of there, STS has been dealing with its own visibility issues and will likely do so through the mid morning. Once the fog burns off, VFR conditions prevail. Rain may need to be introduced if showers are able to hold together and make it past the drier air a loft today. Otherwise, rain should hold off until late tonight or Wednesday morning and it will be coming in from the south.

Vicinity of SFO...Offshore winds and VFR conditions should prevail today. However, CAMs within the HREF suggest the possibility of showers trying to push in from the south from 17-23Z today. Confidence is low given current radar returns over San Luis Obispo look like, but it will be something to watch. If this does pan out, rain chances may need to be added to the TAF after 12Z Wed as it would favor the faster HREF/CAM solution, rather than the slower NBM PoP and timing. Medium confidence for the forecast.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...Quiet conditions prevail with offshore winds holding and high clouds starting to stream in from the south. Some of the CAMs show showers trying to push into the Central Coast from the south later today, with rain chances increasing late Tuesday night into Wednesday morning. Will need to keep an eye on the TAFs and adjust the forecast if the trend continues to the rain arrival earlier.

MARINE

(Today through Sunday) Issued at 432 AM PST Tue Dec 30 2025

Moderate to fresh east to northeast winds winds and moderate seas will prevail through Wednesday. Fresh to strong southerly breezes return Thursday into Friday with gale force gusts likely. Seas build to become rough Thursday into Friday. Rain returns Wednesday and lasts through the weekend.

BEACHES

Issued at 925 PM PST Mon Dec 29 2025

Perigean spring tides (king tides) return Wednesday - Sunday. This is due to the combination of the full moon on 1/3, lunar perigee on 1/1, and perihelion on 1/3. In other words all three planetary bodies are lined up and close to each other. In addition to the high astronomical tide, the incoming low pressure system will bring strong onshore winds, generating some storm surge. The combination of these factors will bring minor coastal flooding to the low-lying areas near shorelines and tidal waterways during high tide Wednesday through Sunday. At the San Francisco tidal gauge, high tide is expected to be 1.5 ft above normal at 7:51 AM Wednesday, 1.7 ft above normal at 8:41 AM Thursday, 1.8 ft above normal at 9:34 AM Friday, 1.8 ft above normal at 10:26 AM Saturday, and 1.6 ft above normal at 11:18 AM Sunday. These predictions include 0.5 feet of storm surge that will enhance the astronomical tide and flooding threat. High tide varies up to 90 minutes earlier or later along the Pacific Coast and through the San Francisco Bay, respectively.

MTR WATCHES/WARNINGS/ADVISORIES

CA...Coastal Flood Advisory from 5 AM Wednesday to 2 PM PST Sunday for CAZ006-505-506-508-509-529-530.

Cold Weather Advisory until 9 AM PST this morning for CAZ504-506- 510-514>518.

Dense Fog Advisory until 10 AM PST this morning for CAZ506-510.

PZ...None.