Issued at 911 PM PST Sun Dec 14 2025
Fog set in a bit earlier this evening and in particular for the valleys of Sonoma County. As a result, and perhaps you've already guessed this, another Dense Fog Advisory has been issued for the North Bay and East Bay valleys. This will run until 11AM on Monday, which means foggy conditions can be expected for the morning commute. We will need to keep an eye on visibilities for the Santa Clara Valley as well as San Jose and Hollister have already started to drop. For those commuting Monday morning, be sure to check the forecast and current weather and traffic 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 122 PM PST Sun Dec 14 2025 (This evening through Monday)
The interaction between Tule Fog outgrowth from the east, and coastal stratus development from the west, continues to feature as the main short-term forecast issue as a shortwave trough passes over the state. The Salinas Valley has mostly cleared out, and the Monterey-Salinas region has generally cleared out, with lingering coastal stratus observed near Pacific Grove and the immediate coast between Point Lobos and Point Sur. The coastal plain of Santa Cruz County and the San Juan Bautista-Hollister valley region remain socked in, the former extending up the coast of San Mateo County, and the latter connected to the extensive inland stratus that persists across much of the Bay Area valleys. If you look closely at the satellite loop you could make out patches of clearing on the fringes -- the Cloverdale area in extreme northern Sonoma County, Lake Berryessa in northeastern Napa County, parts of Livermore, western sections of Alameda County, and the southwest corner of San Francisco. Overall, there is much more stratus coverage today than we saw this time yesterday. As a result, confidence in the clearing of the North Bay valleys, the northern and eastern sections of Contra Costa County, and even southeastern San Mateo Peninsula and the Santa Clara Valley has decreased. For the moment, the high temperatures today are similar to those from the overnight forecast update, with highs in the lower to middle 50s in the Bay Area valleys, into the middle to upper 40s in eastern Marin County and northern and eastern Contra Costa County, the upper 50s to lower 60s along the Pacific coast, and the middle 60s to the lower 70s in the Salinas Valley. There's a chance that the temperatures could still undershoot the official forecast this afternoon, which comes into play if the clearing out process continues to lag the model projections.
On Monday, conditions are expected to be broadly similar to today's with a similar evolution of the stratus deck, as ridging forms on the backside of the shortwave trough. This ridge is remarkably positively tilted, such that the flow pattern off the California coast is quite zonal. This is a clue to the forthcoming pattern change, and so are the high clouds that are expected to flow over the region, thus increasing the uncertainty over the forecast. Will the high clouds bring breezier flow aloft that could help us scour out the Tule Fog, or will they inhibit solar heating on Monday afternoon and keep the stratus around through the day? For now, have leaned towards another day of slower clearing, and have tamped Monday's lows cooler than the deterministic NBM output gives.
..issued at 122 PM PST Sun Dec 14 2025 (Monday night through next Saturday)
More zonal flow will come to the region on Tuesday, allowing a pattern change which will gradually open the proverbial storm door and lead to wetter conditions through the balance of the 7-day outlook and beyond. The first of the systems will come through Tuesday into Wednesday, with generally beneficial rainfall across our region focused on the North Bay, where rain totals will lie around 0.5-0.75" for the Sonoma coastal ranges, the 0.3-0.5" for the Mayacamas, and 0.1-0.25" for the valleys. South of the Golden Gate, rainfall totals remain generally less than 0.1", with a few hundredths of an inch being the absolute maximum total across the Central Coast. More substantial rain is expected late on Thursday into Friday and the upcoming weekend, with the current forecast showing two distinct pulses of rain, one on Thursday and Friday and another for the upcoming weekend, each with the potential for more significant rainfall totals than the forecast for the Tuesday- Wednesday system. Initial forecasts suggest that rain totals over one inch are possible for the North Bay mountains. Beyond the upcoming weekend, uncertainty becomes high to very high, but ensemble model cluster analysis suggests good agreement in a deep upper level trough setting up in the eastern Pacific, which could support an atmospheric river setup assuming that the moisture plume sets up in the right place. The latest CPC outlooks suggest that the North Bay faces a high risk (over 60% probability) of heavy rain early next week, with the rest of the region seeing a moderate risk (40-60% probability) of heavy rain in addition to the entire Bay Area and the northern Central Coast seeing a moderate risk of strong winds in the 8-14 day period (December 22-28).
(06z TAFS) Issued at 925 PM PST Sun Dec 14 2025
Patchy low clouds and fog are beginning to fill back in over the region. Low cigs and locally dense fog is expected once again tonight. Models indicate cigs will scatter out around 17z-19z. However high clouds drifting in over the region may help mix out the boundary layer a bit resulting in some earlier clearing Monday morning across area terminals.
Vicinity of SFO, VFR conditions prevail currently however areas of patchy low clouds are anticipated to fill back in over the bay tonight. Confidence is low as to the extent of coverage impacting SFO and OAK. Models indicate cigs may stay out of SFO and OAK however satellite imagery indicates rapid spread close to the terminals and will need to watch closely.
SFO Bridge Approach, Low clouds over the approach expected to fill in overnight with locally dense fog.
Monterey Bay Terminals, IFR cigs will prevail through tonight with clearing anticipated after 17z Monday morning.
(tonight through next Saturday) Issued at 911 PM PST Sun Dec 14 2025
Southerly flow will prevail north of Pigeon Point ahead of an approaching frontal system. Light to moderate northwesterly flow will prevail across much of the coastal waters with the exception of areas north of Pigeon Point that will turn increasing to the south ahead of an approaching frontal system. Slightly stronger winds are expected along the immediate coast south of Point Sur through Monday as the first in a series of weak systems reaches the coastal waters. Rain chances increase this week. Light seas will gradually build becoming moderate to rough by mid week.
Ca, Dense Fog Advisory until 11 AM PST Monday for CAZ506-510.
PZ, Small Craft Advisory from 3 PM Monday to 9 AM PST Tuesday for Pt Pinos to Pt Piedras Blancas 0-10 nm.
