, 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.
(00z TAFS) Issued at 530 PM PDT Tue Sep 15 2026
MVFR stratus is hugging the coastline as seen on current satellite imagery, mainly impacting HAF and Monterey Bay sites. Interior East and South Bay valley terminals may be the only sites spared from stratus impacts this TAF cycle, with a 30-40% chance of development as advertised by the SCT decks. Coastal terminals are the first to develop MVFR ceilings which may drop to IFR overnight, followed by the remaining sites around midnight. Medium confidence on the exact arrival of stratus for Bay Area terminals. Moderate onshore breezes ease to gentle overnight before increasing to moderate again by Wednesday early afternoon.
Vicinity of SFO, Stratus has begun to flow through the Golden Gate which will allow for borderline MVFR-IFR ceilings to develop at OAK shortly after sunset. SFO will follow with MVFR ceilings around midnight. Both will remain under these conditions until late Wednesday morning. Moderate to gentle diurnally driven onshore breezes prevail through the TAF period. Medium confidence on the exact onset of MVFR ceilings and scattering times as they may occur a couple hours later than specified.
SFO Bridge Approach, Stratus coverage may be patchy overnight, but generally will be similar to SFO.
Monterey Bay Terminals, MVFR stratus is currently settling into the terminals. As the evening goes on, ceilings will gradually drop to IFR overnight and lift to MVFR Wednesday morning before scattering out by the early afternoon. Gentle onshore winds prevails through the TAF cycle. Medium confidence on the exact timing of when ceilings transition to IFR, back to MVFR, and eventually VFR.
(today through Sunday) Issued at 1029 AM PDT Tue Sep 15 2026
Northwesterly winds diminish across the inner and southern coastal waters today with a moderate breeze and occasional fresh gusts prevailing through late week. Strong northwesterly winds diminish more slowly across the northern outer waters with hazardous conditions continuing into Wednesday. Rough seas linger through Wednesday before seas abate and become moderate.
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.
