Cooler temperatures are expected today and Thursday before trending warmer Friday and Saturday. There is the potential for moderately gusty offshore winds over the North and East Bay hills Thursday and Friday nights.
As of 9:05 AM PDT Wednesday, The marine layer is about 1500 feet deep and current satellite imagery shows coastal low clouds extending well inland this morning. Stratus should be fairly slow to clear from near-coastal areas as the area remains under a moderate onshore flow, with 2.1 mb from SFO to SAC. High temperatures today are forecast to be a few degrees cooler than yesterday in most places, with 60s to lower 70s at the coast, and 80s to lower 90s inland. Some of the warmest inland areas could see highs in the middle 90s.
The upper level ridge off the California coast will continue to weaken as an upper level low drops south from Western Canada into the Pacific Northwest. This will lead to continued cooling during the next couple of days. Thursday will be the coolest day as an upper level disturbance moves south across Nevada with the trough axis moving through our district. This disturbance will tighten an offshore surface pressure gradient with north to northeast winds increasing Thursday night as this trough moves through. The 12Z run of the NAM12 model shows 925 mb winds in the 25 to 35 kt range, strongest winds over the higher terrain in Napa County. After weakening on Friday the north to northeast winds will ramp up once again Friday night as the flow aloft becomes northeast on the back side of the trough bringing another night of potentially gusty winds for the North and East Bay hills Friday night. Currently there are no watches or advisories for the North and East Bay hills but will continue to monitor.
Longer range models indicate a long-wave upper trough over the eastern Pacific, with high pressure over the Rocky Mountain states. This will maintain cool or near seasonally normal temps going into the first week of Summer.
As of 11:00 AM PDT Wednesday, For 18z TAFs. Marine layer deepened to around 2000 feet this morning as the shortwave ridge weakened and onshore flow increased. Winds near the coast have been southerly with anticyclonic rotation associated with coastal eddies over the Monterey and San Francisco Bay feeding stratus into the bays a little longer than expected. Low clouds were widespread this morning and are retreating from inland areas. Stratus is expected to remain along the coast this afternoon with VFR at the TAF sites. Winds will become onshore and increase this afternoon, with most sites experiencing speeds of 10-15 kt. For tonight, onshore flow is expected to persist and a return to MVFR or lower cigs are expected at all terminals by sunrise.
Vicinity of KSFO, Clouds are rapidly decreasing per satellite and web cams with full clearing expected to occur around or shortly after 18z. Winds this afternoon will become onshore and increase with speeds of around 15 kt, and occasional gusts to around 20 kt. Borderline MVFR/IFR cigs will develop overnight tonight and continue through Thursday morning.
SFO Bridge Approach, A slightly thicker area of stratus over SF Bay will result in clearing occurring closer to 19z over parts of the approach. Otherwise, similar to SFO.
Monterey Bay Terminals, MVFR cigs will continue through 19-20z with clearing expected for the rest of the afternoon. Winds becoming onshore with speeds around 10-15 kt. IFR expected to develop early to mid evening with LIFR possible at MRY after midnight continuing through Thursday morning.
As of 8:37 AM PDT Wednesday, Generally light to locally moderate south to southwesterly winds will prevail across the coastal waters with the exception of strengthening northerly winds over the northernmost outer waters. Strong northerly Gale Force winds are forecast to be confined mainly to the northernmost outer waters north of Point Reyes from this evening through at least Thursday evening. Gusty northerly winds will become more widespread across the coastal waters Thursday evening through Friday. This will result in steep fresh swell creating hazardous seas conditions, particularly for smaller vessels.
Today, sca, pt arena to pigeon pt 10-60 nm
