Issued at 913 PM PST Tue Dec 9 2025
Temperatures across the region are running warmer than they were 24 hours ago across the higher elevations and cooler to about the same across the lower elevations. What's the difference between those areas? Fog! Satellite imagery shows a fairly expansive area of fog across the North Bay and East Bay valleys tonight. Sites in Byron, Livermore, and Napa are reporting lowered visibilities around 2-3SM with ceilings around 300 to 500 ft. High resolution model guidance suggests localized dense fog is possible within the delta and San Pablo/Suisun Bay and extending up into the North Bay and East Bay Valleys. If you encounter fog while driving, remember to slow down and prepare for unexpected changes in visibility. For the interior Central Coast, the lack of fog/cloud cover will lead to increased radiational cooling and see temperatures drop into the mid to upper 30s. There may be pockets of low 30s to upper 20s across the higher elevations in that area. If you reside in that area, make sure to bundle up during your morning commute.
, Issued at 1256 PM PST Tue Dec 9 2025 (This evening through Wednesday)
Another day of watching the stratus slowly erode across the Bay area. The North Bay Valleys seem to be on track to erode by mid to late afternoon, which should keep high temperatures fairly chilly up there. It's been fun, yet challenging and humbling experience to try and nail the stratus erosion timing and high temperature forecast. This will continue to be the trend into Wednesday, though hopefully we get a little more compression from the high pressure system and perhaps slightly stronger offshore flow. If that happens, we could see warmer temperatures than forecast; however, I trended with a slightly more pessimistic forecast for Wednesday. If your'e outside the East and North Bay areas, warmer weather is on tap for Wednesday.
The area area to watch will be interior Central Coast temperatures tonight. Ended up tweaking the values in these area based on the past few nights being a touch colder than expected.
, Issued at 1256 PM PST Tue Dec 9 2025 (This evening through Wednesday)
Another day of watching the stratus slowly erode across the Bay area. The North Bay Valleys seem to be on track to erode by mid to late afternoon, which should keep high temperatures fairly chilly up there. It's been fun, yet challenging and humbling experience to try and nail the stratus erosion timing and high temperature forecast. This will continue to be the trend into Wednesday, though hopefully we get a little more compression from the high pressure system and perhaps slightly stronger offshore flow. If that happens, we could see warmer temperatures than forecast; however, I trended with a slightly more pessimistic forecast for Wednesday. If your'e outside the East and North Bay areas, warmer weather is on tap for Wednesday.
The area area to watch will be interior Central Coast temperatures tonight. Ended up tweaking the values in these area based on the past few nights being a touch colder than expected.
..issued at 1256 PM PST Tue Dec 9 2025 (Wednesday night through next Monday)
Heights will build into for the later portion of the work week, leading to high temperatures climbing a few degrees each day. The question will be, what does that mean for our friends who have been stuck with stratus? The ridge should limit the spread of the stratus and fog, due to the marine layer compressing. If any clouds and fog do form, they should at least erode faster leading to smaller warming trend for these areas. High temperatures falter a few degrees as we head towards the weekend as upper level ridging slides eastwards. The next chance for rain may occur early next week. The dates of when this occurs seem to continue to be pushed back, so stay tuned.
(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.
(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.
Issued at 932 PM PST Tue Dec 9 2025
Long period swell will impact the coast Wednesday - Friday. This energy brings strong rip currents, an increased risk for sneaker waves, and large breaking waves. NW swell around 8 feet with a 15 second period will translate to breaking waves up to 15-20 feet. These conditions may warrant a Beach Hazards Statement, particularly with the warm weather likely luring more people to the Beach.
Ca, Beach Hazards Statement from 7 AM PST Wednesday through Friday evening for CAZ006-505-509-529-530.
PZ, Small Craft Advisory until 9 AM PST Wednesday 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 Wednesday for Pigeon Pt to Pt Pinos 10-60 NM.
