textproduct: San Francisco Bay Area

KEY MESSAGES

Updated at 132 AM PDT Tue Oct 21 2025

- Quiet, seasonal conditions through much of the week.

- Slight chance for isolated showers and thunderstorms from Bay Area southward tonight into Wednesday morning.

- Cooler temps and rain chances return Friday evening through the weekend. Higher chances North Bay, low chance Central Coast.

SHORT TERM

Issued at 132 AM PDT Tue Oct 21 2025 (Today and tonight)

Current satellite shows southerly surge of moisture and associated stratus pushing into the Monterey Bay region and up the coast of Santa Cruz and San Mateo counties. These locations can expect areas of dense fog this morning. The marine layer is still very compressed along the coast and well mixed inland thanks to weak offshore flow, so expect another day of mostly clear skies and dry conditions. The offshore pressure gradient begins to reverse ahead of a pattern change slated to take place starting this evening. Deep moisture from an EPac upper low begins advecting into the region this evening, first made apparent by increased mid-to-upper level cloud cover. Good surface moisture spreads much further inland tonight with RH 70-100% region-wide and PWAT approaching 1" by Wednesday morning (approx 160% of normal for this time of year). Deep moisture and marginal lift associated with this upper low will potentially lead to a few isolated showers and thunderstorms overnight tonight into Wednesday morning. Weak flow aloft doesn't promote much in the way of large-scale forcing, and there is still a hint of a dry layer between the moisture aloft and surface moisture. While these aren't terribly noteworthy alone, we are keeping the mention of dry lightning simply because any rain that does fall will likely be below the wetting rain definition of 0.1". Highest likelihood for these impacts to occur looks to be interior Monterey and San Benito counties, coastal waters off the Central Coast and Santa Clara, San Mateo, and Santa Cruz counties. Any shower and thunderstorm activity that does occur should be winding down by just after sunrise Wednesday. Despite a slight risk for dry lightning, overall fire risk remains on the lower end given the moist fuels and recent wetting rains last week.

LONG TERM

Issued at 132 AM PDT Tue Oct 21 2025 (Wednesday through Monday)

By Friday evening, we see our second wave in our big pattern shift. A deep, longwave trough is progged to dig out of the Gulf of Alaska into the PNW. Global ensemble guidance is advertising very good agreement in the timing and overall evolution of this pattern. However, one trend in the forecast has been the northward jog of highest moisture transport. The result is sharp decline in the total amount of rainfall expected through the weekend. Highest totals still expected well north of us, and we may even see a situation where areas south of the Bay Area don't pick up any rain at all from this system. Nevertheless, cooler temps and higher RH will note a change in the season.

AVIATION

(12Z TAFS) Issued at 425 AM PDT Tue Oct 21 2025

Fog and low stratus have moved northward along the coastal areas past the Golden Gate, coming inland across the Monterey Bay region. Not much inland intrusion is expected for the rest of the night, with the marine layer remaining rather compressed. Stratus mixes out through the post-sunrise hours and should be clear from the terminals by 17-18Z. Gentle onshore breezes will develop along the coast with winds remaining light and terrain driven inland. Tonight, the marine layer is expected to expand with an approaching low pressure system, allowing the coastal valleys to develop ceilings. There is some chance of thunderstorms across the Central Coast and extending into the South Bay, but probabilities remain too low to note in the TAFs at this time.

Vicinity of SFO... High confidence of VFR through the TAF period. A gentle west-northwest breeze in the afternoon and evening, with light winds overnight. Wednesday afternoon, some high resolution models are showing light southwest flow over the terminal, but confidence is low to moderate at this time.

SFO Bridge Approach... Similar to SFO.

Monterey Bay Terminals... Another rather complicated LIFR expansion tonight, but both MRY and SNS should now be socked in through around 17-18Z this morning. A light onshore breeze should develop in the afternoon and evening hours, with IFR-LIFR stratus overnight. Some high resolution models are depicting MRY clearing out in the late evening hours, but confidence is low. Chances for convection overnight are too low to note in the TAFs at this time.

MARINE

(Today through Sunday) Issued at 425 AM PDT Tue Oct 21 2025

Winds and seas remain light through the day. A new long period northwest swell arrives early Tuesday night and spreads across the waters, with additional swells arriving Thursday night. Wet weather conditions return by Friday and continue into the upcoming weekend as a storm system approaches from the north.

BEACHES

Issued at 425 AM PDT Tue Oct 21 2025

The Beach Hazards Statement has been extended out in time through 3 AM Thursday as a moderate to long period northwesterly swell impacts all of the Bay Area and Central Coast beaches. Swell heights will ramp up through the day, peaking tonight into Wednesday, with lingering impacts Wednesday evening through early Thursday morning across the Central Coast. These conditions will result in breaking waves of 15 to 20 feet and up to or exceeding 25 feet at favored break points such as Mavericks. Never turn your back to the ocean! Swim near a lifeguard if possible! If caught in a rip current, swim parallel to shore until you escape its influence.

DialH/RGass

MTR WATCHES/WARNINGS/ADVISORIES

CA...Beach Hazards Statement through late Wednesday night for CAZ006- 505-509-529-530.

Dense Fog Advisory until 10 AM PDT this morning for CAZ509- 528>530.

PZ...Small Craft Advisory from 9 PM this evening to 3 PM PDT Wednesday for Pt Arena to Pt Reyes 10-60 NM.

Small Craft Advisory from 3 AM to 3 PM PDT Wednesday for Pigeon Pt to Pt Pinos 10-60 NM.