FXUS66 KMTR 212353 AFDMTR Area Forecast Discussion National Weather Service San Francisco CA 353 PM PST Sun Dec 21 2025 ...New KEY MESSAGES, SHORT TERM, LONG TERM... .KEY MESSAGES... Updated at 344 PM PST Sun Dec 21 2025 - Flood Watch remains in effect through Monday afternoon for the North Bay; extension in time and coverage likely - Moderate to heavy rain overnight into early Monday across the North Bay may lead to minor flooding over roadways overnight into Monday morning, turn around don't drown! - Chances for moderate to heavy rain increase for interior locations south of the North Bay late Tuesday through early Friday, with increasing chances for urban flooding and extensive travel delays - Impactful and likely very hazardous winds Tuesday through early Friday along our entire coastline and higher elevations inland - Dangerous beach conditions likely late Tuesday through Friday for all Pacific Coast beaches && .SHORT TERM... Issued at 344 PM PST Sun Dec 21 2025 (This evening through Monday) Steady rain, moderate to heavy at times, from the ongoing atmospheric river will continue over the North Bay for the remainder of today and through the overnight into early Monday morning. The moisture plume oscillates back to the south, primarily over the Bay Area during the day Monday, with both GFS/ECM IVT values backing off, ranging from 0-250kg/m/s through the day tomorrow. The most recent forecast for the Mark West Creek near Mirabel Heights approaches action stage around sunrise Monday morning where it will level off for the remainder of the day when the rainfall shifts south. Despite the temporary weakening of the atmospheric river, periods of moderate/heavy rain in the Santa Cruz mountains will produce 2-3" from late tonight through Monday evening with lesser amounts expected for the southern Marin coastal ranges and the Santa Lucia, ~1-2" due to a nearly saturated boundary layer near and along the coast. Although much of the area is expected to see some rain Monday, it will be mostly light and on-and-off away from the coastal ranges, with little impact. Might be a good day to make final preparations for the upcoming holiday. Beginning Tuesday, first along the coastline in the morning, then later inland - the wind and the rain ramp back up considerably. && .LONG TERM... Issued at 344 PM PST Sun Dec 21 2025 (Monday night through next Saturday) Confidence is high for the strong winds to begin to develop along our Pacific Coast line Tuesday afternoon into Wednesday morning. A series of disturbances rounding the base of a trough associated with a deepening closed low well to the north will produce 925mb flow over 50kts at times below 80-90kt 500mb flow. By early Wednesday morning, southerly winds along our coast from Big Sur up to Point Reyes may reach 70-80mph at times. It will be very dangerous to spend anytime near our beaches or to be in our coastal waters Tuesday through Friday. The first wave will push a strong cold front through our entire area early Wednesday morning with periods of heavy rain and a slight chance of thunderstorms that could produce strong wind gusts up to 70mph or higher along with brief downpours. The North Bay and coastal ranges have been benefiting the most from rainfall from the atmospheric river out ahead of the powerful upper level low. Its Wednesday through Thursday when much of our interior will see its highest rainfall totals. A High Wind Watch watch is likely to be hoisted over the next 24hrs along our coastal areas, and at least a Wind Advisory for large portions of our interior Wednesday and Thursday (Christmas Day) when gusts may reach 40mph in low-lying areas, and 60mph or higher along inland peaks. A second, maybe slightly less dynamic front pushes through our area Christmas Day through Christmas night, with similar impacts, periods of heavy rain and strong winds. Winds begin to ease and a drier airmass appears to set in over the course of the day Friday into next weekend. Remember, this is still 4-5 days out, the forecast details and timing can and will change as we move through the holiday period. Confidence is high that both Christmas Eve and Christmas Day will see our entire area experience periods of moderate/heavy rain with strong winds. Keep checking back as the forecast is refined over the coming days for improved timing of the worst impacts. && .AVIATION... (18Z TAFS) Issued at 1015 AM PST Sun Dec 21 2025 Current rainband is focused mainly across North Bay and areas north. However, prefrontal showers are still spreading across the Bay Area and Central Coast, with light to moderate showers possible. As this front slowly sags south late this afternoon through the overnight hours, moderate to occasionally heavy rains will develop. The models show this rainband stalling over the Monterey Bay, before lifting back northward on Monday. Therefore, SNS and MRY may not see the rain like the other tafs, and stay more showery in nature. Strong gusty south to southeast winds will also develop this afternoon ahead of and along the front. However, they will drop off behind the front with lighter winds expected across the region tomorrow. Most taf sites will continue to see IFR and MVFR CIGS and VIS. However, there are some exceptions (SJC, LVK, and SNS) that are seeing VFR conditions at this time. Conditions will deteriorate as this band shift south, especially in the pockets of heavier rain. Vicinity of SFO...Light showers and low CIGs continue continue to move through the area into the early evening. Expect southerly winds to increase into the late afternoon and early evening as the main rain band approaches. The added mixing from the increased winds could offer some moments of lifted CIGS, but these look to be short lived. Expect visibilities to suffer as the rain rates increase through the evening. Shower chances thin into the late night as the rain band move farther south, but reform as the front shifts northward into late Monday morning. An Airport Weather Warning has been issue for 23z-05z for gusts at or above 34 kts. SFO Bridge Approach...Similar to SFO. Monterey Bay Terminals...Low clouds (IFR) and MVFR VIS will continue to plague MRY through much of the day, while SNS is seeing VFR CIGS and VIS. Gusty south winds will develop this evening ahead of the front, but should weaken during the early morning hours. Expect reduced visibilities from rainfall as the band focuses over the area through the end of the TAF period. && .MARINE... (Today through Friday) Issued at 1015 AM PST Sun Dec 21 2025 Rainfall intensity increases through through the day today across the northern waters with a strong cold front sagging southward to near Pigeon Point by this evening. Gusty southerly winds increase along the front today before weakening into Monday. A more substantial period of unsettled weather enters the picture Tuesday with a gale force low forecasted to enter the coastal waters. This system appears likely to bring near storm force and isolated hurricane force gusts to the waters south of Pigeon Point and near Point Sur Tuesday night into Wednesday morning. Seas build through the week and will be very hazardous to mariners with the potential for wave heights in excess of 20 feet. && .MTR WATCHES/WARNINGS/ADVISORIES... CA...Flood Watch through Monday afternoon for CAZ502>506. PZ...Gale Warning until 9 PM PST this evening for Mry Bay-Pigeon Pt to Pt Pinos 0-10 nm-Pt Arena to Pt Reyes 0-10 nm-Pt Arena to Pt Reyes 10-60 NM-Pt Pinos to Pt Piedras Blancas 0-10 nm- Pt Reyes to Pigeon Pt 0-10 nm-SF Bay N of Bay Bridge. Small Craft Advisory until 3 AM PST Monday for Pigeon Pt to Pt Pinos 10-60 NM. && $$ SHORT TERM...JM LONG TERM....JM AVIATION...Palmer MARINE...Palmer 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