Issued at 838 AM PST Fri Dec 12 2025
Satellite imagery shows extensive stratus coverage in the North Bay valleys, the interior East Bay, and the Santa Clara valley, with some dissipating stratus lingering over the San Mateo Peninsula. A Dense Fog Advisory was issued for the valleys of the North bay, interior East Bay, and South Bay due to widespread dense fog observations, especially in the Sonoma County valleys and the San Jose area, effective through 11 AM. No other changes to the forecast at this time.
DialH
, Issued at 1214 AM PST Fri Dec 12 2025 (Today and tonight)
The same general pattern persists dominated by a slow moving ridge, light offshore flow, and persistent stratus and fog focused on the North and East Bay valleys. The strong temperature inversion and offshore winds are creating adiabatically warmed winds along the coast and nice beach weather. Sunny Half Moon Bay reached 72 degrees today and spent roughly 7 hours in the 70s. Meanwhile, thick fog continued to impact the San Pablo Bay region, and San Rafael only made it to 48 degrees. It's not often that Half Moon Bay is 24 degrees warmer than San Rafael, outside of the last few days anyway. I hate to say it again, but Friday will be more of the same. The stratus looks like it will be slightly less expansive and the South Bay will be the biggest benefactor of this change. We're continuing to add a persistence nudge to the forecast to help capture the wide range of max temperatures we've seen across the region recently.
..issued at 1214 AM PST Fri Dec 12 2025 (Saturday through Thursday)
The long range trend is a gradual shift away from this prolonged dry period to a more active, wetter pattern. The end is finally in sight for this ridiculously resilient ridge we've been dealing with since December 4th. The ridge axis will finally slide to our East on Saturday. We'll still likely have the Tule fog impacts through the weekend, but the pattern shift will be felt with slightly cooler temperatures in the sunny areas. The change will be subtle though as we remain in backside of the ridge through Monday. The 500 mb flow becomes zonal in the middle of the week. This new pattern, combined with a plume of 1.2"+ PW should bring some light rain from Tue-Wed, focused on the North Bay. The more active zonal pattern will transition to a low-amplitude ridge Thursday- Friday, although some light rain is still possible with lingering high PW. The most interesting part of the forecast is the following weekend. It's looking more and more likely that a deep trough and associated high moisture plume will bring an Atmospheric River to the Bay Area. The Climate Prediction Center now has a moderate risk of both heavy precipitation and high winds across the Bay Area and Central Coast from 12/19-12/22. December is typically the wettest month for San Francisco, where the normal monthly rainfall for is 4.76". While we haven't had any rain since 11/20, the upcoming sequence will start to chip away at this deficit and there is more rain possible the following week. Long range ensembles show about a 25% chance of getting 3+" between now and the 26th.
(12z TAFS) Issued at 318 AM PST Fri Dec 12 2025
Tule fog continues to blanket the Central Valley, Sacramento River Delta, and the North Bay and East Bay valleys. LVK, STS, and APC will certainly be dealing with ceiling and visibility impacts through the morning. SJC has stayed clear so far, but the temperature has dropped to 39F with a 38F dew point, indicating radiation fog will soon form. All terminals should clear in the afternoon with a similar timing as seen yesterday.
Vicinity of SFO, Only a 20% chance of developing IFR ceilings or fog. Even if these conditions materialize, the impacts should be brief, as observed yesterday. Otherwise winds will favor a NE direction and remain gentle all day.
SFO Bridge Approach, Similar to SFO.
Monterey Bay Terminals, Light offshore flow will keep the skies clear all day. There is a slight chance for impacts Saturday morning as a weak southerly surge may develop and bring stratus up the Central Coast.
(today through Wednesday) Issued at 838 AM PST Fri Dec 12 2025
Gentle NE winds will gradually shift to southerly by Saturday morning as moderate to rough seas subside to a slight 3 feet from Saturday through Monday. These favorable conditions are rare for winter. A moderate westerly swell will return by Tuesday with moderate westerly winds arriving Wednesday.
Issued at 1214 AM PST Fri Dec 12 2025
Long period NW swell is causing hazardous beach conditions Friday. This energy brings strong rip currents, an increased risk for sneaker waves, and large breaking waves. This coincides with nice warm weather, which will likely lure more people to the beach under a false sense of security. A Beach Hazard Statement is in effect through Friday evening. Respect the power of the ocean and never turn your back on it.
Ca, Beach Hazards Statement through this evening for CAZ006-505-509- 529-530.
Dense Fog Advisory until 11 AM PST this morning for CAZ506-510- 513.
PZ, None.
