566 FXUS66 KMTR 210836 AFDMTR Area Forecast Discussion National Weather Service San Francisco CA 136 AM PDT Tue Oct 21 2025 ...New SHORT TERM, LONG TERM... .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... (06Z TAFS) Issued at 928 PM PDT Mon Oct 20 2025 Winds are becoming light across much of the area. Cloud cover is building from from the south and filling into the Monterey Bay, and looks to arrive at the terminals in the earl night. Cloud cover will slowly build to HAF into the late night. Along with low CIGs, pockets of fog look to affect the Monterey Bay terminals. Expect widespread clearing and VFR into the mid to late morning with light to moderate winds expected for the afternoon. Winds weaken again into Tuesday evening, with CIGs build in the early evening along the coast, affecting HAF and the Monterey Bay terminals. Cloud cover begins to push into the North Bay into the mid evening affecting STS with additional cloud cover spreading south into the late night. Vicinity of SFO...VFR through the TAF period. Winds reduce into the night, becoming light and variable through the night and into Tuesday morning. These winds increase slightly and turn westerly into the mid afternoon, but become light and variable again into Tuesday night. SFO Bridge Approach...Similar to SFO. Monterey Bay Terminals...Winds reduce into the night, and becoming light and variable in the late night as LIFR CIGs build. Moments of fog affect the terminals through the early to mid morning. Expect VFR to return into the late morning as cloud cover and fog erodes and moderate winds return. Cloud cover returns in the early evening on && .MARINE... (Tonight through next Sunday) Issued at 928 PM PDT Mon Oct 20 2025 Winds and seas are reducing and look to remain light through much of Tuesday. 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 200 PM PDT Mon Oct 20 2025 The Beach Hazards Statement has been extended out in time through 9 PM Wednesday as a moderate to long period northwesterly swell impacts all of the Bay Area and Central Coast beaches. 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. RGass && .MTR WATCHES/WARNINGS/ADVISORIES... CA...Beach Hazards Statement through late Wednesday night for CAZ006- 505-509-529-530. 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. && $$ SHORT TERM...Behringer LONG TERM....Behringer AVIATION...Murdock MARINE...Murdock Visit us at www.weather.gov/sanfrancisco Follow us on Facebook, X, and YouTube at: www.facebook.com/nwsbayarea x.com/nwsbayarea www.youtube.com/nwsbayarea