Swell Matrix

Area Forecast Discussion

National Weather Service San Francisco CA

1049 am PDT Thu Mar 12 2026

Update

Issued at 839 AM PDT Thu Mar 12 2026

Currently clear skies across the region this morning as we kick off the start of our warming trend. Temperatures this morning are running anywhere from 3 to 10 degrees warmer than at this time yesterday with portions of the higher elevations up to 15 degrees warmer. High temperatures for much of the interior will be in the upper 70s to low 80s today with slightly cooler temps in the 60s to 70s directly along the coastline. This is the start of a potentially long duration heat event with even warmer temperatures expected next week. As always, when spending time outdoors make sure to listen to your body, drink plenty of water, and allow time to rest.

Short Term

, Issued at 225 AM PDT Thu Mar 12 2026 (Today through Saturday)

Temperatures around 15 degrees above normal are expected today as the region is on the eastern periphery of upper-level shortwave ridging across the Eastern Pacific Ocean. Fortunately the location of the ridge will maintain onshore flow which will keep things comfortable at night and temperatures from running away. The only record high in jeopardy today is SJC with a maximum temperature forecast of 81 degrees which would tie the record from 2007. A passing upper-level shortwave trough to the north will tamp down the ridge and reinforce onshore flow, pressing pause on the warming trend Friday into Saturday. Of most impact in the short term will be minor HeatRisk. To mitigate your risk: increase hydration with water, reduce time spent outdoors or stay in the shade when the Sun is strongest, and open windows at night and use fans to bring cooler air inside buildings. With roughly 50% of our population not having air conditioning, it is going to be essential that all preparations are taken to keep places of residence as temperature controlled as possible. Examples include turning your blinds upwards and closing them during the day, ensuring ceiling fan direction is counterclockwise, and keeping windows open at night to take advantage of the natural air conditioning that is onshore flow.

Long Term

..issued at 225 AM PDT Thu Mar 12 2026 (Sunday through Wednesday)

Global ensemble clusters are in agreement that an anomalously high amplitude upper-level longwave ridge will begin to move into the region from the Eastern Pacific Ocean Sunday. As the aforementioned ridge encroaches our area, winds will veer to become northerly which will further warm and dry the region as the sea breeze circulation is turned off. The axis of the ridge is expected to be overhead on Tuesday, which will yield the hottest day of the forecast period, before slowly drifting into the Colorado River Valley. While beyond the official seven day forecast, there is uncertainty in the evolution of the ridge. Even with the uncertainty, global ensemble clusters illustrate that it is likely that we will be dealing with anomalously high heights through Friday of next week. We will be in record breaking territory Sunday through Wednesday not only for daily records, but monthly records too. Forecast record breaking 850 mb temperatures and 500 mb heights are leading to a 50% probability that SJC reaches 90 degrees - this would be the first time ever in the month of March. It goes without saying that this is going to be the hottest that we have been this calendar year. Impacts wise, widespread minor HeatRisk on Saturday will give way to areas of moderate HeatRisk Sunday through Wednesday. To mitigate your risk: reduce time in the Sun during the warmest part of the day, stay hydrated with water, stay in a cool place during the heat of the day, move outdoor activities to cooler times of the day, and for those without a/c, use fans to keep air moving and open windows at night.

Aviation

(18z TAFS) Issued at 1049 AM PDT Thu Mar 12 2026

VFR through the TAF period for all but HAF which will see moments of low CIGs and haze into Friday morning. Mostly moderate winds build in the mid afternoon, staying below 15 kts. Winds reduce into the evening and night, becoming light across the region. Moderate winds return Friday afternoon.

Vicinity of SFO, VFR through the TAF period. Moderate west winds build in the mid afternoon, peaking around 14 kts. These winds linger into the night before reducing as scattered low clouds filter into the SF Bay. Winds build again into Friday afternoon.

SFO Bridge Approach, Similar to SFO.

Monterey Bay Terminals, VFR through the TAF period. Moderate northwest winds build into the afternoon and last into the evening and early night before becoming light. Winds stay variable for MRY overnight, while SNS goes northerly into the early night, then Northwest into Friday morning.

Marine

(today through Tuesday) Issued at 839 AM PDT Thu Mar 12 2026

Breezy to gusty northerly winds continue across the outer waters through the weekend. Winds will eventually increase near shore late Friday. The stronger winds will result in locally hazardous conditions. Winds and seas ease into the next work week.

Watches, Warnings, Advisories

Ca, None. PZ, Small Craft Advisory from 9 AM Friday to 3 AM PDT Saturday for Pt Arena to Pt Reyes 0-10 nm-Pt Pinos to Pt Piedras Blancas 0-10 nm.

Small Craft Advisory from 3 PM Friday to 3 AM PDT Saturday for Pt Reyes to Pigeon Pt 0-10 nm.

Small Craft Advisory until 3 AM PDT Saturday for Pigeon Pt to Pt Pinos 10-60 NM-Pt Arena to Pt Reyes 10-60 NM.

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