FXUS66 KMTR 010028 AFDMTR Area Forecast Discussion National Weather Service San Francisco CA 428 PM PST Wed Dec 31 2025 ...New AVIATION... .KEY MESSAGES... Updated at 1247 PM PST Wed Dec 31 2025 - High astronomical tides combined with storm surge will bring minor to moderate coastal flooding around high tide through Sunday. - A prolonged rainy period starts today. - Strong southerly winds are likely Friday and into Saturday morning. && .SHORT TERM... Issued at 1247 PM PST Wed Dec 31 2025 (This evening through Thursday) Light to occasionally moderate rain continues to spread northward and will increase in coverage and intensity through this evening. This is a result of PWAT values between 1.00-1.30" advecting in from the south as a mid/upper level cut off low remains just west of the Central Coast. As the low pressure shifts into the Central Coast on Thursday morning, there will be a slight chance of thunderstorms late morning into the afternoon over this region. By late Thursday afternoon and into the evening, rain will be more focused along the coastal terrain as a warm front moves northward across the region. Rain shadowed valleys may not see any rainfall from Thursday afternoon through about Friday night. && .LONG TERM... Issued at 1247 PM PST Wed Dec 31 2025 (Thursday night through next Tuesday) A more typical atmospheric river is set to move through the region late Friday and into early Saturday morning. This is when more widespread rain and stronger winds are forecast. Wind gusts are currently forecast to be 45-55 mph along the coast, in the higher terrain, and northwest to southeast oriented valleys. Elsewhere expecting 35-45 mph gusts from late Friday night through Saturday morning. Wind Advisories are likely during this time frame, yet the forecast models have trended about 6 hours later from yesterday. So, still refining the forecast as we move closer to the event. From 4 PM Friday through 4 PM Sunday, rainfall totals will range from 2.00- 4.00" in the coastal ranges, 1.50-3.00" in the North Bay, 1.00-2.00" in San Francisco and other coastal areas, and generally less than 1.25" in the rain shadowed valleys. There is generally less than a 20% chance of thunderstorms as the main frontal band moves through and in wake of the passage through Sunday afternoon. Given the recent rainfall from last week, this will lead to nuisance flooding for poor drainage areas, urban areas, and rises on flashy creeks/streams. This will be especially so if a heavier rain shower and/or thunderstorm where to move over any give area. However, widespread river flooding is not anticipated at this time. From the previous forecaster: "A new low pressure system and associated cold front is possible Monday or Tuesday. The ensemble clusters have differing opinions on the strength and timing of this feature, but they all show a trough off the coast, which is enough to keep rain chances around through the entire 7-day forecast period. KMUX will stay in precip mode for the foreseeable future." && .AVIATION... (00Z TAFS) Issued at 343 PM PST Wed Dec 31 2025 A persistence forecast through the TAF period with MVFR cigs and mostly steady light rain for all terminals. During breaks in precip conditions could lift to VFR and during periods of more intense rainfall, down into IFR. There is also a slight chance for an isolated thunderstorm, with confidence too low to mention in the TAF. Mostly easterly winds this evening and overnight, veer to southerly and increase, becoming gusty after sunrise Thursday as an offshore upper level system moves northeast over our outer waters. Vicinity of SFO...MVFR cigs expected to prevail through the forecast period with some potential for IFR cigs/vis in times of more intense rainfall. Winds veer from easterly this evening through the overnight, to more southerly after sunrise Thursday morning with occasional gusts up to 20-25mph. SFO Bridge Approach...Similar as SFO. Monterey Bay Terminals...MVFR cigs expected to prevail through the forecast period, with easterly component winds this evening becoming more southerly during the overnight period as the offshoresystem moves northeast overnight. KSNS is expected maintain southeast surface flow, gusty at times with the valley influence. && .MARINE... (Today through Monday) Issued at 859 AM PST Wed Dec 31 2025 Moderate to fresh winds and moderate seas continue into Thursday. Widespread light rain and a low potential for thunderstorms across the southern waters continues into Thursday. Winds rapidly strengthen from strong to gale force by early Friday as a second, stronger, system arrives. Periods of moderate to heavy rain and a slight potential for thunderstorms are expected Friday into Saturday. Winds diminish early Sunday but breezy conditions and rain showers continue into next week. && .BEACHES... Issued at 859 AM PST Wed Dec 31 2025 Perigean spring tides (King Tides) will impact the region through Sunday. This is due to the combination of the full moon on 1/3, lunar perigee on 1/1, and perihelion on 1/3. In other words all three planetary bodies are lined up and close to each other. In addition to the high astronomical tide, the incoming low pressure system will bring strong southerly winds, generating some storm surge. The combination of these factors will bring minor to moderate coastal flooding to the low-lying areas near shorelines and tidal waterways during high tide through Sunday. At the San Francisco tidal gauge, high tide is expected to be 2.0 ft above normal at 8:41 AM Thursday, 2.2 ft above normal at 9:34 AM Friday, 2.2 ft above normal at 10:26 AM Saturday, and 1.8 ft above normal at 11:18 AM Sunday. These predictions include up to 1 foot of storm surge that will enhance the astronomical tide and flooding threat. High tide varies up to 90 minutes earlier or later along the Pacific Coast and through the San Francisco Bay, respectively. && .MTR WATCHES/WARNINGS/ADVISORIES... CA...Coastal Flood Advisory until 2 PM PST Sunday for CAZ006-505-506- 508-509-529-530. PZ...Small Craft Advisory until 3 PM PST Thursday for Pigeon Pt to Pt Pinos 10-60 NM-Pt Arena to Pt Reyes 0-10 nm-Pt Reyes to Pigeon Pt 0-10 nm. Small Craft Advisory from 9 PM Thursday to 3 AM PST Friday for Pt Arena to Pt Reyes 0-10 nm-Pt Arena to Pt Reyes 10-60 NM. Gale Warning from 3 AM to 9 AM PST Friday for Pt Arena to Pt Reyes 0-10 nm-Pt Arena to Pt Reyes 10-60 NM. Small Craft Advisory from 8 PM Thursday to 9 AM PST Friday for Pigeon Pt to Pt Pinos 0-10 nm-Pt Reyes to Pigeon Pt 0-10 nm. Small Craft Advisory from 9 PM this evening to 3 PM PST Thursday for Pigeon Pt to Pt Pinos 0-10 nm-Pt Arena to Pt Reyes 10- 60 NM. Small Craft Advisory until 9 PM PST this evening for Pt Pinos to Pt Piedras Blancas 0-10 nm. Gale Warning from 9 PM this evening to 3 PM PST Thursday for Pt Pinos to Pt Piedras Blancas 0-10 nm. Small Craft Advisory from 3 AM to 9 AM PST Friday for Pigeon Pt to Pt Pinos 10-60 NM. && $$ SHORT TERM...RGass LONG TERM....RGass AVIATION...JM MARINE...Kennedy 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