FXUS66 KMTR 140033 AFDMTR Area Forecast Discussion National Weather Service San Francisco CA 433 PM PST Sat Dec 13 2025 ...New AVIATION, MARINE... .KEY MESSAGES... Updated at 1216 PM PST Sat Dec 13 2025 - Stratus persists over the North and East Bay valleys and the coastal regions - Wetter conditions return for the upcoming work week && .SHORT TERM... Issued at 1216 PM PST Sat Dec 13 2025 (This evening through Sunday) The upper level ridge that brought us the days of stable weather is beginning to move off to the east, and an shortwave trough has set up across the State. Satellite imagery reveals that stratus persists across the valleys over the North Bay and interior East Bay valleys in addition to the southeastern part of San Mateo County, outgrowths of the Tule Fog across the Central Valley, and the immediate coastal regions near Point Reyes, San Mateo County, and south of Point Sur, as a southerly surge takes hold just off the coast. There is low to very low confidence in any clearing across the coastal regions, the Sonoma County valleys, the 101 corridor of Marin County, and the northern and eastern parts of Contra Costa County. Everywhere else, some clearing is possible through the rest of the afternoon. High temperatures will be broadly similar to those yesterday. The coldest regions will be the eastern part of Marin County and the northern and eastern regions of Contra Costa County, where highs will remain in the middle to upper 40s. At the other extreme, the interior Central Coast valleys, shielded from both the coastal stratus and the Tule Fog, reach the middle to upper 70s. In general, the Bay Area valleys see highs in the middle 50s to lower 60s, although lingering stratus in the Sonoma County valleys makes the high temperatures a little uncertain, with the potential for the region to remain in the 40s if the stratus persists all day. On Sunday, the shortwave trough crawls across the state and ridging redevelops on its backside, with conditions expected to be broadly similar to today's. && .LONG TERM... Issued at 1216 PM PST Sat Dec 13 2025 (Sunday night through next Friday) As we head into the early part of upcoming work week, the ridge will continue to flatten, a pattern change that brings more zonal flow to the region by Tuesday. This new pattern should help scour out the Tule Fog and, when combined with a plume of moisture with PWAT values up to 1.25 inches, brings a chance of light rain to the region Tuesday and Wednesday, with rainfall totals focused on the North Bay. A weak ridge will move through the state on Thursday and Friday, but the overall flow should remain generally zonal and lingering showers and drizzle are possible from remnant moisture in the region. Towards and beyond the end of the 7-day outlook, the forecast points towards another round of wet weather across the region for the weekend of the 20th and 21st as a deep trough in the eastern Pacific coincides with another plume of moisture moving through the West Coast. With a system this far out, details are still very much in flux. The CPC maintains a strong lean (60-80% probability) towards rainfall totals above the seasonal average in the 6-10 day window (December 19-23). Beyond that, the CPC maintains a moderate risk (40- 60% probability) of heavy rainfall and high winds into the Christmas holiday period with a 60-70% probability of rainfall totals above the seasonal average through the 8-14 day period (December 21-27), which would impact any holiday travel plans. && .AVIATION... (00Z TAFS) Issued at 432 PM PST Sat Dec 13 2025 Mix of VFR and MVFR thanks to Tule Fog approaching from the east and marine stratus from the west. Winds are generally light across the board with locally breezier conditions along the coastline. Highest confidence in MVFR CIGs but in areas impacted by fog (STS, APC, LVK, SJC ) IFR-LIFR CIGs and visibilities down to 1/4SM are possible. Confidence is lower that visibilities will lower below 4-5SM in areas that are impacted by marine stratus (likely OAK, SFO, MRY, SNS, and HAF). Generally followed persistence timing for when CIGs will clear tomorrow (generally around 19-20Z) with model guidance indicating potential for clearing closer to 18-19Z. Fog and stratus are likely to return again tomorrow night. Vicinity of SFO...VFR becoming MVFR overnight. Confidence is moderate that any CIGs that reach SFO tonight will be MVFR with guidance indicating at least some potential for IFR CIGs to temporarily develop. LAMP guidance shows around a 20% chance chance of LIFR conditions developing between 13-17Z. Clearing is expected by 19Z with VFR through the remainder of the TAF period. Winds stay light and variable to offshore through tomorrow afternoon when a moderate sea breeze looks to develop. SFO Bridge Approach...Similar to SFO. Monterey Bay Terminals...Stratus is right on the edge of the Monterey Peninsula with stratus intermittently impacting MRY this afternoon. Kept MVFR conditions as the prevailing for MRY through later this evening with stratus arriving at SNS by 02-03Z. CIGs lower to IFR-LIFR overnight with some potential for visibilities to drop down to 1/4SM early tomorrow morning. Confidence was low that visibilities would decrease that low at MRY and SNS so only pushed visibilities down to 4SM with the 00Z TAF update. LAMP guidance suggests visibilities will fluctuate throughout the night so a tempo may be needed to address visibility decreases. && .MARINE... (Tonight through next Friday) Issued at 432 PM PST Sat Dec 13 2025 A weak surface low pressure circulation over the outer coastal waters will result in gentle to moderate southerly breezes. Winds will veer to become northwesterly tomorrow night. Seas will remain moderate through Monday, building to become rough in the outer waters and northern inner waters by Tuesday. Several disturbances passing to the north next week will bring renewed rain chances and wind shifts. && .MTR WATCHES/WARNINGS/ADVISORIES... CA...None. PZ...None. && $$ SHORT TERM...DialH LONG TERM....DialH AVIATION...Kennedy MARINE...Canepa 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