Swell Matrix

Area Forecast Discussion

National Weather Service San Francisco Bay Area

432 am PDT Tue may 17 2022


Look for warming inland temperatures through the weekend. Breezy winds are likely each afternoon and evening; becoming particularly gusty and turning offshore for Wednesday into Thursday. Elevated fire weather concerns are anticipated for mid to late week as humidity values plummet.


As of 02:28 AM PDT Tuesday,

Today and Tonight:

Quasi-zonal flow will be replaced by weak troughing today as the upper feature passes by with little fanfare. Subtropical high pressure will prevail over the eastern Pacific while lower pressure persists over the Great Basin and Desert Southwest. These features will allow onshore flow to continue with sometimes gusty conditions along the coast. A warming trend is anticipated for inland areas with highs mostly in the 80s, while cooler 60s and 70s will prevail along the coasts and within the marine-influenced valleys. Nocturnal stratus early this morning around Monterey Bay should wane by late morning with models indicating much lower chances for formation tonight as the upper trough departs and surface high pressure noses in from the west.

Wednesday and Thursday:

Deep layer ridging will flex poleward across the eastern Pacific while downstream troughing drops through the Pacific Northwest and northern Great Basin. This will maintain robust northerly flow across the area with a tendency for winds to become more offshore and gusty. This pattern change will result in: 1) warmer temperatures as highs for inland areas climb well into the 80s to lower 90s; 2) stronger winds as gusts in the hills may reach or exceed 45 mph; and 3) enhanced fire weather concerns as very low humidity values combine with warm temperatures and gusty winds. As previously mentioned fuels aren't fully in fire season *yet* but they are getting there. Otherwise look for plentiful sunshine outside of some coastal clouds at times.

Friday through Monday:

Upper troughing will gradually depart towards the east as the upper ridge further builds into CA. The pressure gradient should relax with time allowing winds to subside, however minimum relative humidity values should remain on the low side away from the coast. Very warm temperatures are likely to prevail inland, as model indications suggest some areas could climb well into the 90s by early next week.


As of 4:32 AM PDT Tuesday, For the 12Z TAFs. VFR except IFR-MVFR due to patchy morning coastal stratus. Breezy to gusty onshore winds mostly from afternoon to evening. Winds easing tonight and Wednesday morning.

Vicinity of KSFO, VFR, breezy west wind except strong and gusty again this afternoon and evening.

KSFO Bridge Approach, Similar to KSFO.

Monterey Bay, Patchy stratus /IFR-MVFR/ this morning otherwise VFR. Breezy to gusty onshore winds late morning and afternoon.


As of 4:28 AM PDT Tuesday, Northwesterly gale force wind gusts across the coastal waters today through Wednesday, quite likely again Thursday and Friday. Strong and gusty onshore winds across the bays each afternoon and evening through midweek. Strong winds will persist through the week generating steep and hazardous seas at periods of 7 to 9 seconds.

Watches, Warnings, Advisories

Today, sca, pt reyes to pigeon pt 0-10 nm until 9 am sca, pigeon pt to pt pinos 0-10 nm until 9 am sca, pigeon pt to pt piedras blancas 10-60 nm until 9 am glw, pt reyes to pigeon pt 0-10 nm from 9 am glw, pigeon pt to pt pinos 0-10 nm from 9 am glw, pigeon pt to pt piedras blancas 10-60 nm from 9 am glw, pt arena to pt reyes 0-10 nm glw, pt pinos to pt piedras blancas 0-10 nm glw, pt arena to pigeon pt 10-60 nm sca, mry bay sca, SF Bay from 9 am

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