textproduct: San Francisco Bay Area

KEY MESSAGES

Updated at 1224 AM PST Wed Dec 10 2025

- Hazardous beach conditions through Friday.

- Tule fog and stratus continue for the North and East Bay.

- Light rain remains possible next week.

SHORT TERM

Issued at 1224 AM PST Wed Dec 10 2025 (Today and tonight)

Tule fog and stratus continue with very similar coverage to 24 hours ago. In addition to the entire Central Valley, most of the North Bay and the interior East Bay are impacted by this persistent radiation fog. This is caused by unmoving high pressure bringing clear, dry, and calm conditions to the troposphere. Combined with long December nights, nocturnal radiative cooling from both the Earth's surface and cloud tops are enhanced. Since the cooling is coming from the bottom up, it's very stable (cold air sinks). And since the cooling at night is enough to reach saturation and form or bolster the existing clouds, a positive feedback loop sets up where the clouds then block incoming sunlight during the day. All this works to keep the day-time temperatures cool under the clouds, and the models have been struggling to capture just how cool. Kentfield stayed between 43 and 46 degrees all day Tuesday. The forecast is challenging because there is very warm air just above the clouds. The 850 temperature has blown past the 90th percentile is now approaching the daily max on record. Boulder Creek stayed clear and reached 78 degrees yesterday. This big discrepancy between the thin cold layer and everything else is really tough to nail down. When the advanced weather models let us down, we often fall back on the most rudimentary form of forecasting in existence: persistence. In other words, what happened yesterday will happen today. Specifically Tuesday's high temperatures are making up 66% of the forecast for Wednesday. With an unchanging pattern, that's not a bad guess. If the clouds clear early though, watch out for temperatures to spike. Areas outside of the clouds (Central Coast, SF Peninsula) will have cooler mornings and warmer afternoons. Maybe just a couple degrees warmer than yesterday.

LONG TERM

Issued at 1224 AM PST Wed Dec 10 2025 (Thursday through Tuesday)

Temperatures should climb a degree or two each day through Friday before the ridge axis finally moves through on Saturday. That will mark the end of this prolonged boring pattern as a more zonal jet stream moves in. We should finally see some high clouds by Sunday with a chance for rain starting Monday or Tuesday. While we are finally losing the ridge, we're not getting a substantial trough, so any rain bearing systems should be relatively light. On the other hand the active zonal flow could bring these weaker systems in quick succession. CW3E shows both the ECCC and NCEP AR activity anomaly peaking around +2 AR days per week from 12/15-12/21 before falling back to near the climatological norm for the following 2 weeks. In other words if we don't get any substantial rain next week, there is no strong signal for it to come during the rest of the month. Perhaps the best chance is around the 20th, but there's a lot of uncertainty. The 00Z ECMWF ensemble members range from 0.0" to 8.4" of total rain at SFO through the 21st. So the total dispersion is massive, but the more reasonable interquartile range is 0.4" - 2.0". The GEFS is drier with a medial closer to 0.5". Temperatures will cool this weekend, but should remain warmer than normal through next week. The CPC temperature outlooks are about as confident as we ever see that it will remain warmer than normal for the next couple weeks, but that doesn't necessarily take our famous microclimates into account.

AVIATION

(06Z TAFS) Issued at 944 PM PST Tue Dec 9 2025

Additional warming in the lower levels of the atmosphere per recent Oakland upper air sounding data and Bodega Bay profiler data, strengthened the lower level temperature inversion today. However, the difference between ground level and the base of the temperature inversion so far has not changed much since early evening, at least not yet. The SAC-SFO pressure gradient is 1.5 mb and the WMC-SFO 1.6 mb. The WMC-SFO gradient is forecast to strengthen tonight and Wednesday, both gradients support ongoing offshore winds tonight and Wednesday.

The synoptic pattern remains favorable for plentiful tule fog and low stratus to continue over the Central Valley, corresponding to ongoing chilly temperatures and higher surface pressures in the valley. There'll be very little if any interference in outgoing radiative cooling tonight; it's dry above the lower level temperature inversion and cirrus clouds will be at a minimum tonight. Expect redevelopment of fog and stratus /LIFR-IFR/ in our area including the potential for dense tule fog /VLIFR/ to be transported into the Bay Area on light offshore winds tonight and Wednesday. Key to mix out times, if they are earlier tomorrow than recently observed, will be the base of the lower level temperature inversion, if it does not move downward much then it's a persistence forecast with late day break out times if at all. In areas where VFR has prevailed recently the probability of VFR or mixing out from late night and morning fog and stratus /VFLIFR-IFR/ is greater for Wednesday. This is a very challenging forecast, forecast confidence regarding mix out times Wednesday is low.

Vicinity of SFO...VFR initially forecast tonight, then low to moderate confidence IFR tempo stratus ceiling develops 08z-12z then IFR prevailing to 18z Wednesday. The combination of radiative cooling and light offshore surface winds increases the probability of stratus /IFR/. Will need to closely monitor satellite and surface observations for potential fog development as well. Offshore winds are forecast to prevail during the 06z TAF.

SFO Bridge Approach...Slant range visibility moderate to poor at sunrise and sunset due to trapped hazy conditions. Light offshore winds may end up bringing low stratus and fog to the SFO approach later tonight and Wednesday morning.

Monterey Bay Terminals...The highest probability of VFR is here, though radiative cooling may result in patchy fog to patchy dense fog /LIFR-VLIFR/ in the Salinas Valley tonight and Wednesday morning. Cold air drainage winds will result in southeasterly winds tonight and Wednesday, possibly shifting to light and variable temporarily Wednesday afternoon. Cold air drainage winds redevelop Wednesday night and Thursday morning.

MARINE

(Tonight through next Monday) Issued at 929 PM PST Tue Dec 9 2025

High pressure will result in northerly winds over the coastal waters. High pressure will also build over the Great Basin tonight and Wednesday resulting in additional offshore winds across the Delta to the San Francisco Bay. Winds will strengthen across all outer waters by midweek. A new, long period northwesterly swell is expected Wednesday, lasting into the early weekend.

BEACHES

Issued at 1224 AM PST Wed Dec 10 2025

Long period swell will reach the coast Wednesday - Friday. This energy brings strong rip currents, an increased risk for sneaker waves, and large breaking waves. The Bodega Bay Buoy is reporting a WNW swell of 9 feet with a 13 second period. That translates to breaking waves of 12-16 feet along west facing beaches. 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.

MTR WATCHES/WARNINGS/ADVISORIES

CA...Beach Hazards Statement from 7 AM PST this morning through Friday evening for CAZ006-505-509-529-530.

PZ...Small Craft Advisory until 9 AM PST this morning for Pt Pinos to Pt Piedras Blancas 0-10 nm.

Small Craft Advisory until 3 AM PST Thursday for Pt Arena to Pt Reyes 10-60 NM.

Small Craft Advisory until 3 PM PST this afternoon for Pigeon Pt to Pt Pinos 10-60 NM.