Swell Matrix

Area Forecast Discussion

National Weather Service San Francisco Bay Area

426 am PDT Sat apr 1 2023


Cool temperatures persist through mid next week with slight rain chances Saturday and Monday, otherwise mostly drier. Potential for gusty winds across the area Monday. Drying out and warming up late next week as temps approach normal by next weekend.


As of 03:45 AM PDT Saturday, Mostly quiet weather this weekend as an elongated trough sits to our north and the nose of the jet sits off the Oregon coast, leaving us on the wrong side for any large-scale lift. However, a weak shortwave trough embedded in the flow will bring a very weak surface trough through our area Saturday afternoon. Many may see sprinkles, particularly from the SF Bay northward, but chances of measurable precip remain low. In fact, the North Bay has the highest chance, and that chance is still only about 20% of seeing at least 0.01".

By Monday, a much deeper low is progged to drop southward over the western US, placing a more substantial surface low over the Great Basin. As a steep longwave ridge replaces the trough in the Gulf of Alaska, this sets us up well for a rather gusty wind event on Monday. Current placement of the jet streak around the base of the upper trough suggests the highest wind threat along the central coast, including much of Monterey County and the Big Sur coast. This scenario is also well supported in ensemble guidance. Probabilistic guidance suggests about a 70-90% chance of gusts of at least 41 kts (47 mph), and a 30-50% chance of gusts of at least 48 kts (55 mph) along the Big Sur coast, Santa Lucia, and the crest of the Santa Cruz mtns. Elsewhere at lower elevations north of Monterey county, there is about a 40-60% chance of gusts to at least 34 kts (40 mph). Chances for high winds diminish inland in the North Bay, where it currently looks like gusts of this magnitude will likely be confined to the highest hills and coastal areas. Winds will gradually weaken into Monday night as the upper low moves eastward. Chilly temperatures follow with Tuesday morning and Wednesday mornings being the coldest with lows in the upper 30s to low 40s.

Beyond Monday, confidence is increasing in a ridging pattern setting up over the West Coast, promoting drier weather and gradually bringing our temperatures back up towards normal with highs in the upper 60s to low 70s by next weekend (low-to-mid-60s coastal).


As of 4:25 AM Saturday. For the 12Z TAFs. Terminals currently reporting predominantly VFR conditions. Patches of mid level stratus are thought to exist, but coverage of high clouds throughout the region is making it difficult to gauge coverage. A cursory inspection of the AlertCalifornia cameras suggests that they're not very widespread. Based on this, have elected to remove IFR conditions from the STS and APC forecasts for the rest of the night. Light winds persist through the night, then an breezy westerly flow as a weak cold front passes through the region, bringing MVFR ceilings and some scattered showers, particularly in the higher elevations. Around a 10-20% probability that IFR conditions develop as the front passes through any particular terminal. Northwesterly flow and clearing skies expected after the cold front passes.

Vicinity of SFO, VFR with breezy westerly winds through the day, before a weak cold front comes through this evening. MVFR ceilings expected with a low confidence (10-20% probability) of IFR conditions developing. Scattered showers possible in the higher elevations of the San Mateo hills, but probabilities are low (less than 10%) and those at the terminal lower still. Clearing skies and northwest winds after the front passes early Sunday morning.

SFO Bridge Approach, Similar to SFO.

Monterey Bay Terminals, VFR with light northwest flow expected through the evening, when a weak cold front passes through with MVFR ceilings and a low confidence (less than 10% probability) of scattered showers, especially in the higher elevations. Low to moderate confidence (30-40% probability) of IFR conditions developing at MRY, if only for a short period. The front is expected to pass after the end of the TAF period early Sunday morning, with clearing skies and a renewed onshore flow pattern.


As of 03:46 AM PDT Saturday, Generally light winds prevailing Saturday prior to the arrival of a weak cold front Saturday night. Northwest winds strengthening through the remainder of the weekend and into early next week in the wake of a stronger cold front resulting in isolated rain showers. Seas remaining largely wind driven through the weekend with a mid- period swell building early next week.

Watches, Warnings, Advisories

Today, none.

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