Issued at 914 AM PDT Sat Aug 29 2026
Extended the Dense Fog Advisory through 10 AM for the North Bay Valleys, however seeing some improvement in visibilities across the 101 Highway Corridor with Navato now at 1 mile while Petaluma and Santa Rosa/Sonoma County Airport both at 1/2 mile. Expecting mostly sunny conditions regionwide as low clouds and fog dissipate. Still expecting seasonably cool temperatures today as the trough of low pressure deepens off of the Pacific Northwest coast. No updates planned as the ongoing forecast remains on track this morning.
RGass
, Issued at 909 PM PDT Fri Aug 28 2026 (Tonight through Sunday)
While there were some light showers Friday, the lightning never happened and that threat is now over. The 00Z sounding measured 1.32" of precipitable water. That's well over the 90th percentile (1.04"), and near the maximum recorded for this date (1.38"). Despite this near record moisture, dry air is moving in from the northwest remarkably fast. The ECMWF ensemble mean predicts the PW will drop from 1.38" Friday to around 0.5" Saturday. That means the atmospheric moisture is decreasing from well over the 90th percentile all the way down to the 10th percentile in only 12-24 hours.
As a result of the much drier air, the skies will be mostly clear Saturday. The marine layer is trying to re-organize, but any stratus will likely be patchy and evaporate in the mid to late morning. The mid and high level clouds are already clearing and will not return anytime soon. Despite the sunshine, temperatures will remain several degrees cooler than normal this weekend.
..issued at 909 PM PDT Fri Aug 28 2026 (Sunday night through next Friday)
Upper level troughing will persist through the week, with a few embedded shortwave features bringing some early rain to the Pacific Northwest. In the Bay Area, rain is less likely, but the cooling trend will continue through at least the middle of the week. Max temperatures will be roughly 10-15 degrees below normal from Monday through Wednesday. The 850 mb temperature is expected to drop below the 25th percentile (16.1C) by Tuesday morning.
(12z TAFS) Issued at 421 AM PDT Sat Aug 29 2026
IFR-LIFR stratus is developing into the Sonoma County valleys, through the Golden Gate into the SF Bay Area, and across Monterey Bay and into the northern Salinas Valley. Limited further expansion is forecast tonight as the marine layer remains relatively compressed at around 1000-1500 ft deep. Stratus will retreat to the immediate coast after sunrise with moderate onshore pattern winds developing in the afternoon and evening hours. Tonight, lower confidence in the ceiling heights as a deepening marine layer should result in some higher ceilings, but otherwise the stratus deck should return to most of the areas that it currently covers.
Vicinity of SFO, IFR stratus over the immediate terminal area will persist through the post-sunrise hours, moderate confidence on the clearing time. Moderate west-northwest winds with strong gusts will develop in the afternoon and evening, with stratus returning to the terminal area tonight.
SFO Bridge Approach, Lower confidence for stratus development along the approach path through the morning. Otherwise similar to SFO.
Monterey Bay Terminals, LIFR stratus and patchy fog continue through the morning. Gentle to moderate northwest winds will develop in the afternoon and evening hours, with stratus returning somewhat early in the evening hours.
(today through Thursday) Issued at 914 AM PDT Sat Aug 29 2026
Northwest winds remain fresh with strong to near gale force gusts today into Sunday night. In response, wind driven seas build to rough this afternoon and steadily subside to moderate through next week. A long period southerly swell also peaks today around 17 to 18 seconds and gradually diminishes by Sunday night.
Ca, Dense Fog Advisory until 10 AM PDT this morning for CAZ506.
PZ, Small Craft Advisory until 3 AM PDT Sunday for Mry Bay-Pigeon Pt to Pt Pinos 0-10 nm.
Small Craft Advisory until 3 AM PDT Monday for Pt Arena to Pt Reyes 0-10 nm-Pt Arena to Pt Reyes 10-60 NM.
Small Craft Advisory until 9 PM PDT Sunday for Pigeon Pt to Pt Pinos 10-60 NM-Pt Pinos to Pt Piedras Blancas 0-10 nm.
