Marine Weather and Tide Forecast for South San Francisco, CA

SHORT TERM
(This evening through Wednesday)
Issued at 218 PM PDT Tue Apr 22 2025

Short Term Key Messages *Slight chance for drizzle and patchy dense fog *Cooling trend begins

A shortwave trough passes over the PacNW Wed into Thu, placing weak troughing over us. This will increase onshore flow during this period, which should allow the marine layer to deepen and penetrate farther inland. Modest moisture looks to come with the onshore flow and that should lead to pockets of drizzle late tonight and into Wed morning. The most favorable areas look to be on along the coast, the Monterey Bay area, and perhaps around San Francisco Bay, in addition to areas with orographic lift. Currently have the drizzle/fog potential ending around 11AM, with stratus clearing for the North, East, and South Bay interior valleys. Coastal communities may struggle a bit longer and could potentially see stratus and drizzle linger to lunch time. High temperatures will range from near normal to about 10 degrees below their normal for this time of year.
Ridges, gaps, and perhaps even some associated channels/valleys may see gusts up to 20-35 mph Wed afternoon and evening.

LONG TERM
(Wednesday night through next Monday)
Issued at 218 PM PDT Tue Apr 22 2025

Long Term Key Messages *Increased onshore flow and a cooling trend through Saturday *15-45% chance for drizzle/light rain Friday/Saturday

Onshore flow continues into Thu, pushing more moisture into the region. This should lead to another cloudy night with pockets of drizzle, similar to Tue night into Wed morning. Skies look to be mostly cloudy during this time frame with more a brief period of zonal flow setting up. Another cool day will be on tap with high temperatures around 5 to 15 degrees below their normal. The signal for gusty ridge, gap, and associated valley/channels shows up again where they peak around 20-35 mph Thu afternoon and evening.

By Friday, models and cluster analysis agree that an upper level troughing deepens. There is still some uncertainty as to how strong or how far south this system goes and if it closes off. There is some agreement that it has shifted a bit more south, which has increased the PoP forecast across the region with the highest amounts being in the North Bay and for higher elevation terrain.
Confidence still remains a bit on the lower side for rainfall accumulation as we're still only expecting light rain or drizzle.
The latest forecast gives a smattering of a 0.01-0.10" for those in the North Bay mountains, along the Bay Area coast, and into the Central Valley mountains. This will likely change over the next few days as we get closer to the event.

As we head into early next week, clusters show upper level troughing moving east with upper level ridging returning. This should put temperatures closer to their seasonal normals.

AVIATION
(18Z TAFS)
Issued at 1017 AM PDT Tue Apr 22 2025

Currently a mixed bag of IFR-VFR across the board with brief widespread VFR expected this afternoon. High confidence in all terminals experiencing a reduction to at least MVFR overnight as an upper-level trough deepens the marine layer, allowing it to penetrate further inland. Onshore flow will prevail through the TAF period.

Vicinity of SFO...Currently VFR with offshore flow. High confidence in MVFR conditions returning to the terminal overnight.
Winds will prevail out of the west once the sea breeze kicks in this afternoon.

SFO Bridge Approach...San Mateo Bridge Approach continues to clear with the low clouds remaining within the San Francisco Bay expected to clear by the top of the hour.

Monterey Bay Terminals...Currently IFR with westerly flow at MRY and MVFR with northerly flow at SNS. Stratus is expected to continue retreating back toward the coast with VFR expected at both terminals by this afternoon. Both terminals have an 80% chance of IFR conditions returning this evening. Westerly winds will prevail through the TAF period.

MARINE
(Today through Sunday)
Issued at 913 AM PDT Tue Apr 22 2025

Strong northwesterly winds over the outer waters will continue through Wednesday with gale force gusts expected over the northern outer waters. Rough seas will be expected in the outer waters through Wednesday. Moderate northwesterly winds and moderate seas will prevail Thursday through Saturday with a chance for light rain or drizzle Friday.

MTR WATCHES/WARNINGS/ADVISORIES
CA...None.
PZ...Small Craft Advisory until 3 AM PDT Thursday for Pigeon Pt to Pt Pinos 10-60 NM-Pt Arena to Pt Reyes 0-10 nm.

Small Craft Advisory until 9 AM PDT Wednesday for Pt Reyes to Pigeon Pt 0-10 nm.

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

Small Craft Advisory until 3 PM PDT this afternoon for Pt Arena to Pt Reyes 10-60 NM.

Gale Warning until 9 AM PDT Wednesday for Pt Arena to Pt Reyes 10-60 NM.