, Issued at 309 AM PST Tue Jan 20 2026 (Today and tonight)
A ridiculously resilient ridge continues to dominate our short term forecast. The main short term edit was to bump up dense fog potential for the North and East Bay Valleys and to lower forecast morning temperatures for the interior valleys by a few degrees. There is some indication that fog is forming along the North and East Bay Valleys and San Pablo Bay/Delta region. As of 2:30AM the Napa County airport is reporting a visibility of 3/4SM, the Petaluma Airport is reporting 1 1/2SM, and Byron is reporting less than 1/4SM visibility and dense fog. Early morning commuters in the North and East Bays should be prepared for sudden changes in visibility and allow extra time to reach their destinations.
We can expect temperatures to be slightly cooler today compared to yesterday as the upper level ridge starts to break down and a cut- off low approaches the West Coast. Ahead of the cut-off low, we are starting to see some cold air advection which is resulting in a slight cooling trend. To contextualize this, the 00Z sounding recorded an 850 mb temperature of -13.6 C. Model guidance shows 850 mb temperatures gradually cooling to around 10C by early Wednesday and cooling further Wednesday into Thursday as the cut- off low arrives. The cooling trend will be most noticeable across the higher elevations where temperatures will drop from the 70s back into the mid 60s. For Tuesday, temperatures across the Bay Area will generally be in the low to mid 60s while temperatures across the Central Coast will be in the mid 60s to low 70s. Expect another round of fog tonight into tomorrow morning across the North and East Bay Valleys.
..issued at 309 AM PST Tue Jan 20 2026 (Wednesday through Monday)
The upper level ridge will continue to break down Wednesday into Thursday as a cut-off low approaches the West Coast. This cut-off low will move down the coast of California Thursday and Friday before being absorbed into an upper level trough over much of the United States. As the low moves down the coastline, it will bring a surge of slightly moister air (PWAT values around 1") to southern California. This moister air will clip southern Monterey County and bring a slight potential for showers in the Santa Lucia Range. The current forecast grids have a 10-20% probability of precipitation across the southern coastal waters and southern Monterey County late Wednesday into early Thursday. No real accumulation is expected from this system as the bulk of the moisture (and rain) will be well to our south. Ridging rebuilds over the West Coast by late Saturday/early Sunday and remains in place into next week. The next chance for widespread rain still looks likely end of January/beginning of February with models consistently showing a deep upper level trough moving into the West Coast. Worth noting that ECMWF ensemble members have started gaining confidence with nearly every member showing at least some precipitation during that timeframe. There's still a wide range in timing and amounts so we'll have to see how this shapes up as it gets closer.
Temperatures remain seasonal through the long term forecast with highs in the upper 50s to low 60s Wednesday through Monday. The exception will be for the interior Central Coast which will see a slight warming trend into the mid to upper 60s starting Saturday. Overnight low temperatures generally stay in the 40s for much of the long term but some locations do drop into the upper 30s again starting Saturday. Winds remain light through the forecast period with fog likely overnight Wednesday. There is some potential for more widespread fog Thursday and Friday nights but current thinking is leaning more towards the return of stratus over fog. Model guidance shows the marine layer deepening to around 1000 ft starting Thursday which would support the return of stratus to the interior. Either way, the potential for degraded visibility and potential to impact morning commutes will continue for much of the upcoming week. Anyone driving early in the morning should be prepared in the event they encounter fog and experience a sudden drop in visibility.
(12z TAFS) Issued at 339 AM PST Tue Jan 20 2026
Largely still a persistence forecast with a couple of slight caveats. For terminals along the Delta (incl. KAPC), Tule fog is making a bigger impression this morning, along with stronger offshore winds. The fog will likely mix out through this morning over areas of western Solano and Contra Costa counties. However, higher than usual easterly offshore winds look to persist through much of today. Otherwise VFR across the board with some slight reductions in VIS along coastal areas thanks to more BR in the air.
Vicinity of SFO, Still looking at light winds with a slight NE component through the mornings. Looking at a bit higher chance of reduced VIS this evening, but low confidence holds back any further sig reduction in flt cat noted in TAF.
SFO Bridge Approach, Similar to SFO.
Monterey Bay Terminals, VFR. Most notable change with this TAF issuance is the potential reintroduction of marine stratus along the coast from MRY peninsula to Central Coast by the end of this TAF period. Confidence low in impacts to terminals, but there are at least some hints at low cloud decks into Wednesday morning.
(today through Sunday) Issued at 309 AM PST Tue Jan 20 2026
Gentle to moderate breeze continues across the waters early this week. Winds increase late week to a strong breeze by Friday. Weak storm system over the eastern Pacific will result in moderate northwest swell as well, promoting rough seas across the northern outer waters.
Ca, None. PZ, None.
