Issued at 903 PM PST Sat Dec 13 2025
A Dense Fog Advisory has been issued for the North and East Bay valleys this evening and continues until 11AM Sunday as visibilities have faltered to a quarter mile or less. If you're heading out this evening or going out Sunday morning, dense fog can be expected in these areas. Be sure to check the forecast and current weather conditions before heading out and allow extra time for your commute. If driving, slow down, use your headlights (not your high beams), and leave plenty of distance ahead of you.
, Issued at 1216 PM PST Sat Dec 13 2025 (This evening through Sunday)
The upper level ridge that brought us the days of stable weather is beginning to move off to the east, and an shortwave trough has set up across the State. Satellite imagery reveals that stratus persists across the valleys over the North Bay and interior East Bay valleys in addition to the southeastern part of San Mateo County, outgrowths of the Tule Fog across the Central Valley, and the immediate coastal regions near Point Reyes, San Mateo County, and south of Point Sur, as a southerly surge takes hold just off the coast. There is low to very low confidence in any clearing across the coastal regions, the Sonoma County valleys, the 101 corridor of Marin County, and the northern and eastern parts of Contra Costa County. Everywhere else, some clearing is possible through the rest of the afternoon.
High temperatures will be broadly similar to those yesterday. The coldest regions will be the eastern part of Marin County and the northern and eastern regions of Contra Costa County, where highs will remain in the middle to upper 40s. At the other extreme, the interior Central Coast valleys, shielded from both the coastal stratus and the Tule Fog, reach the middle to upper 70s. In general, the Bay Area valleys see highs in the middle 50s to lower 60s, although lingering stratus in the Sonoma County valleys makes the high temperatures a little uncertain, with the potential for the region to remain in the 40s if the stratus persists all day.
On Sunday, the shortwave trough crawls across the state and ridging redevelops on its backside, with conditions expected to be broadly similar to today's.
..issued at 1216 PM PST Sat Dec 13 2025 (Sunday night through next Friday)
As we head into the early part of upcoming work week, the ridge will continue to flatten, a pattern change that brings more zonal flow to the region by Tuesday. This new pattern should help scour out the Tule Fog and, when combined with a plume of moisture with PWAT values up to 1.25 inches, brings a chance of light rain to the region Tuesday and Wednesday, with rainfall totals focused on the North Bay. A weak ridge will move through the state on Thursday and Friday, but the overall flow should remain generally zonal and lingering showers and drizzle are possible from remnant moisture in the region.
Towards and beyond the end of the 7-day outlook, the forecast points towards another round of wet weather across the region for the weekend of the 20th and 21st as a deep trough in the eastern Pacific coincides with another plume of moisture moving through the West Coast. With a system this far out, details are still very much in flux. The CPC maintains a strong lean (60-80% probability) towards rainfall totals above the seasonal average in the 6-10 day window (December 19-23). Beyond that, the CPC maintains a moderate risk (40- 60% probability) of heavy rainfall and high winds into the Christmas holiday period with a 60-70% probability of rainfall totals above the seasonal average through the 8-14 day period (December 21-27), which would impact any holiday travel plans.
(06z TAFS) Issued at 950 PM PST Sat Dec 13 2025
Stratus is spreading into coastal airports (HAF, MRY, SNS, SFO) while fog is impacting several interior airports (STS, APC). Pushed back the arrival of fog to LVK to 09Z but otherwise fog/stratus arrived early to on time this evening. Current thinking is that sites experiencing stratus will see MVFR-IFR conditions while interior sites that are expected to see fog will, at least temporarily, see IFR to LIFR conditions. Continued a persistence forecast of clearing between 19-20Z with some sites potentially clearing closer to 21Z. Guidance backed off of favoring clearing around 18Z and is now more in line with persistence clearing times. Fog and stratus are likely to return again tomorrow night given the current weather set up. Winds remain light and variable but become more moderate and onshore during the afternoon/evening hours.
Vicinity of SFO, MVFR with some potential for IFR overnight. MVFR CIGs have reached SFO and are starting to fill in across the SF Bay. Low to moderate confidence that IFR CIGs will at least temporarily develop overnight. Winds stay light and variable for much of the night before strengthening slightly and shifting onshore again during the day.
SFO Bridge Approach, Stratus filtering in across the SF Bay will result in a loss of VAPS on the SFO Bridge approach. This is likely to persist through 19-20Z (similar to SFO) but some guidance does indicate it could take longer for stratus over the bay to clear than over land.
Monterey Bay Terminals, IFR-MVFR. CIGs are on the border of IFR (MRY) and MVFR (SNS) with both airports to drop to the IFR-LIFR border later tonight. Visibilities are currently forecast to decrease to 3-4SM but GFSLAMP guidance shows some potential for 1/4SM visibilities and fog to develop at MRY between 12-16Z. Leaned towards clearing around 20Z for both sites but it could occur slightly earlier around 19Z. Winds stay light through much of the forecast period with a weak sea breeze developing during the afternoon/evening hours.
(tonight through next Friday) Issued at 903 PM PST Sat Dec 13 2025
A gentle to moderate breeze continues across the coastal waters through this weekend. Winds increase to moderate to fresh across the southern coastal waters Monday as the first in a series of weak systems reaches the coastal waters. Rain chances increase early to midweek with light rain possible for much of next week. Low seas persist through the remainder of the weekend before building to moderate to rough by mid next week.
Ca, Dense Fog Advisory until 11 AM PST Sunday for CAZ506-510.
PZ, None.
