Issued at 847 PM PDT Tue Sep 15 2026
Satellite imagery this evening looks a little different than 24 hours ago. We've talked about the marine layer making a come back and the evening satellite fog product shows it's definitely happening. Stratus remains just north of Pt Reyes and stretches southward Monterey Bay. Interestingly enough coastal stratus then disappears along the Big Sur coast. Why? Most likely lingering Big Sur jet combined with weak eddy effect per wind directions noted on weather stations. Do expect this area to eventually fill in with clouds overnight. We have clouds, but what's the initial marine layer depth? Profilers and an ACARs flight from OAK show the depth in the 1100-1400 foot range. For the rest of the evening expect stratus to expand and move farther inland thanks to a solid 3mb plus onshore gradient.
No update needed this evening.
Other item of note this evening is a solid heat signature. While not in our forecast area, the Dome Fire near Yosemite has notable heat on it cause some pixel saturation on a few ABI satellite bands. In other words, it's hot.
, Issued at 1051 AM PDT Tue Sep 15 2026 (This afternoon through Wednesday)
The marine layer has returned, but it's not uniform. A mesoscale, low-level, cyclonic eddy has formed off the coast of San Mateo County. This is producing easterly, offshore winds in the North Bay and westerly, onshore winds across the Central Coast. The morning sounding measured the marine layer at 1,200 feet deep over Oakland. Surface-based marine layer detection shows it's more shallow to the north and deeper to the south. The marine layer in Sonoma County is around 800 feet deep with near normal temperatures and mostly clear skies. Meanwhile it's around 2,000 feet deep across Monterey County, where max temperatures are around 10 degree below normal, and most of the coast was under overcast skies this morning.
The synoptic scale pattern features a trough over the west coast and a ridge over the SE US. At 500 mb, the trough will become cut-off over the next 24 hours and settle somewhere over Northern California. As a result, temperatures will be cooler than normal today and even more so tomorrow. This low will also bring stronger winds Wednesday afternoon, with gusts of 20-30 mph expected across the East Bay Hills, Salinas Valley, and both the San Francisco and Monterey Bays.
..issued at 1051 AM PDT Tue Sep 15 2026 (Wednesday night through next Monday)
The cut-off low will certainly deepen the marine layer Wednesday night, and it may provide enough lift to support some drizzle Thursday morning. After losing upper level support, the low will gradually weaken through the day. As a result, winds will be much calmer Thursday afternoon. Temperatures will remain roughly 5-10 degrees below normal.
The remnants of the cut-off will gradually move off to the NE and eventually get caught up in the jet stream flow again. We should be on the backside of the trough by Friday, with a weak short-wave ridge building Saturday. This feature looks short-lived as another cut-off low approaches the coast Sunday or Monday. Temperatures should return back to normal Fri-Sun with typical marine layer impacts.
By next week the forecast confidence really falls apart. A few of the deterministic global models show deep, reinforcing trough bringing much cooler weather. The ensembles, however, reveal that this is an outlier in the total guidance envelope. The ensemble mean is much more benign, and there is at least an equal likelihood of warm ridging next week. The ECMWF ensemble actually shows anywhere from 5C to 25C 850 mb temperatures by the middle of next week. That pretty much covers all of the historical possibilities for this time of year. In other words, we don't yet know what's going to happen next week.
(06z TAFS) Issued at 925 PM PDT Tue Sep 15 2026
Currently a mixed bag of IFR-VFR. Stratus is at or within five miles of all terminals and rapidly expanding. As such, all terminals are expected to get MVFR ceilings tonight with a late-morning clearing time. Reasonable worst case scenario is an increase in onshore winds will delay or even prohibit clearing. Diurnal winds will prevail.
Vicinity of SFO, Currently VFR with westerly flow. Stratus is quickly advancing and is expected to form a ceiling shortly. MVFR conditions will likely prevail through the morning with an early return slated for tomorrow night. Diurnal winds will prevail.
SFO Bridge Approach, Similar to SFO.
Monterey Bay Terminals, Currently MVFR with westerly flow at both terminals. MVFR conditions will likely prevail through the morning with an early return tomorrow night. Stratus will stick close to the coast during the afternoon with a possibility that the terminals, especially MRY, remain MVFR through the TAF period. Diurnal winds will prevail.
(tonight through next Monday) Issued at 925 PM PDT Tue Sep 15 2026
Moderate northwest to northerly winds prevail across the outer waters as occasional fresh to strong gusts gradually diminish by Wednesday afternoon. West to southwest moderate breezes dominate over the Bays with strong gusts resulting in hazardous conditions for small crafts on Wednesday. By Friday, widespread northwest to northerly breezes increase to fresh. Wind driven rough seas subside to moderate by Wednesday evening and will remain slight to moderate into the weekend.
Ca, None. PZ, Small Craft Advisory from 9 AM to 9 PM PDT Wednesday for SF Bay N of Bay Bridge.
Small Craft Advisory from 3 PM to 9 PM PDT Wednesday for Mry Bay.
Small Craft Advisory until 3 PM PDT Wednesday for Pt Arena to Pt Reyes 10-60 NM.
