Swell Matrix

Area Forecast Discussion

National Weather Service San Francisco CA

452 pm PDT Wed Sep 23 2026

Short Term

, Issued at 223 PM PDT Wed Sep 23 2026 (This evening through Thursday night)

Our marine layer will continue to degrade off the coast with low expectations for it to rebuild significantly overnight. Persistent onshore winds remain light into Thursday with a weak push of offshore flow overnight across the higher elevations. Due to the lack of low clouds, temperatures climb into the mid 80s to lower 90s across the interior North/East/South Bays with the Central Coast experiencing inland temperatures up to the mid 90s. As a result, pockets of moderate HeatRisk persist today into tomorrow afternoon, specifically along the San Pablo Bay shoreline, interior East/South Bay and Central Coast valleys, as well as the Big Sur coastline. Remember to stay hydrated by drinking plenty of water, wearing sunscreen and light clothing. The Pacific coastline along the Bay Area and Monterey Bay regions remain cooler in the 60s to lower 70s. Similar conditions are expected to continue Thursday morning as the marine layer is expected to remain confined to the coast with poor humidity recoveries overnight. Thursday afternoon, however, marks the beginning of a transition period towards cooler conditions due to an increased push of strong onshore winds ahead of an incoming dry cold frontal passage.

Long Term

..issued at 223 PM PDT Wed Sep 23 2026 (Friday through next Tuesday)

After a couple of days of above normal temperatures, things will begin to transition as we round out the end of the work week and venture into the weekend. On the synoptic scale the region will be in the wake of an upper trough that is forecast to swing eastward through the Pacific NW. Largely NW breezes are anticipated as the diffuse frontal boundary slides southward, however, portions of the Central Coast (largely the Santa Lucia Range) may experience brief periods of N to even NNE'ly breezes as surface pressure rises across the northern Sac Valley late Friday into Saturday. Fortunately, the probability for widespread wind gusts exceeding 30 to 35 mph remains under 10%, except across Pacific Coast waters.

The upper air pattern will remain somewhat amplified this weekend and into early next week. Broad/diffuse troughing along the Pacific Coast should translate to some degree of onshore flow. It doesn't appear that the marine layer will deepen through 3,000 feet (or at least deepen it quickly) with the tail end of some of the hi-res guidance suggesting around 1500-2000 ft. For elevations toward the higher end of this range, cross-sections do indicate RH potentially as low as the mid-teens which may set the stage for extended periods of dryness, particularly during the overnight hours. Should this signal in the NWP persist, fire weather headlines for poor overnight humidity may be warranted this weekend and into early next week. Additionally, we'll need to monitor the progression of the marine layer as it'll have ramifications on the temperature forecast as we progress through the weekend. Should the marine layer not deepen as much, it'll be highly probable that upward adjustments to MaxT (and downward adjustments to RH) will be needed. For now, the official forecast will roll with the deterministic NBM which keeps temperatures in the 60s along the coast to the low to mid 80s across the interior. Outside of occasional coastal drizzle/mist/fog, there doesn't appear to be any real opportunity for widespread rainfall in the next week or so.

Aviation

(00z TAFS) Issued at 440 PM PDT Wed Sep 23 2026

VFR conditions across the area will continue through sunset into the later evening hours. Moderate confidence in LIFR conditions for the terminals closest to the coast developing after midnight and lingering into mid-Thursday morning. High confidence in more typical diurnal pattern of IFR/LIFR ceilings for the Monterey Bay sites.

Vicinity of SFO, Moderate confidence in MVFR/IFR ceilings developing in the pre-dawn hours and continuing through mid- Thursday morning with VFR through the remainder of the forecast period. A deepening trough to the north will result in a stronger push of onshore flow late in the TAF period with gusty winds expected to set in Thursday night.

SFO Bridge Approach, Similar to SFO.

Monterey Bay Terminals, MVFR ceilings are expected after sunset with IFR/LIFR ceilings after midnight persisting through the middle of Thursday morning with VFR conditions for the remainder of the forecast period thereafter.

Marine

(tonight through next Monday) Issued at 440 PM PDT Wed Sep 23 2026

Northerly breezes will remain moderate to fresh over the outer waters resulting in hazardous conditions for small craft through Wednesday night. By Thursday afternoon and evening, strong gusts will occur nearshore in the favored wind prone areas. Friday will see an increase in northwest winds accompanied by seas building back up to rough, and continuing into the weekend.

Watches, Warnings, Advisories

Watches, Warnings, Advisories

Ca, None. PZ, Small Craft Advisory until 5 AM PDT early this morning for Pigeon Pt to Pt Pinos 10-60 NM-Pt Arena to Pt Reyes 0-10 nm.

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

CA, None. PZ, Small Craft Advisory from 3 PM to 9 PM PDT Thursday for Pigeon Pt to Pt Pinos 0-10 nm-Pt Arena to Pt Reyes 0-10 nm.

Small Craft Advisory from 9 PM Thursday to 3 AM PDT Friday for Pt Pinos to Pt Piedras Blancas 0-10 nm.

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

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