, Issued at 315 AM PST Fri Dec 19 2025 (Today and tonight)
KMUX is in 215 which means we are tracking precipitation across the region. Light rain showers are possible through the morning in the Bay Area, primarily favoring the North Bay and coastal areas. Other coastal/higher terrain areas can expect drizzle. High clouds are beginning to stream into the region from a surface low and its attendant cold front in Oregon. Surface high pressure near the California/Mexico border and surface low pressure in the Gulf of Alaska are creating a conveyor belt of subtropical moisture into California. By this afternoon, the main rain band will trek south into the North Bay, losing its strength as it treks farther south. The passage of the cold front will also increase winds with gusts up to 25 mph expected along the coast, across ridgelines, and through gaps and passes. Today's rainfall is expected to be beneficial. The one critical exception is the Pickett Fire burn scar. There are some hi-res models showing the burn scar approaching its hourly rain rate threshold. Upon further investigation, it seems to be keying on precipitation in the Mayacamas Mountains. Still, it is too high of an impact to not mention. Those who live or travel through the area should be aware of the threat and know that it will persist through the forecast. The aforementioned cold front will become stationary tomorrow. This along with the persistent moisture will allow for rain to continue through the day.
..issued at 315 AM PST Fri Dec 19 2025 (Saturday through Thursday)
Saturday is the earliest that we expect rainfall to transition from beneficial to impactful with at least some impacts expected by Sunday. As such, we are monitoring the need for a potentially prolonged Flood Watch starting somewhere in the Saturday/Sunday timeframe, but no issuance has been made yet. For now, you should monitor later forecasts and those living in areas prone to flooding should be prepared to take action. The exact onset time of impactful rainfall is still uncertain as it will be highly dependent upon antecedent conditions and how this system performs in comparison to its forecast. The most likely rainfall impacts as of now look to be flooding of low-lying, poor drainage, and urban areas as well as flashy creeks/streams such as Mark West Creek in Sonoma County. Once again, these impacts may start as early as Saturday, with at least some impacts expected by Sunday. These impacts can be expected through the duration of the event, with impacts expected to worsen through the event as soils become saturated.
A surface low developing off the North Bay Coast will be responsible for Sunday's weather. The closer proximity of the low (as compared to the Pacific Northwest) will bring greater impacts than the first system. The firehose of subtropical moisture will continue to take aim at the state, only this time around IVT will remain in excess of 500 kg/ms for near 24 hours rather than briefly peaking like the first system is expected to. Moderate to heavy rainfall is expected across most of the region on Sunday with the Interior Central Coast likely remaining in the light rainfall category. In true atmospheric river fashion, rainfall totals will be highest in southwest facing terrain such as the North Bay Coast, Santa Cruz Mountains, and Big Sur Coast as the moisture fetch runs orthogonal to the terrain, providing the most efficient output. Winds will increase, although they are expected to remain sub-criteria for any product as of now. Gusts up to 40 mph can be expected along the coast, across ridgelines, and through gaps and passes. Any wind impacts will be exacerbated by the rain and vice versa. The combination of wind and moist soils will increase the risk for downed trees. Additionally, any leaves that are left on trees will pose the risk of blocking/clogging storm drains if/when they fall, potentially leading to more flooding. There's also a low chance (15% or less) for thunderstorms. The accompanying cold front will pass through on Monday, bringing yet another day of rain and wind. As of now Monday does not look as impactful as Sunday, but there is still uncertainty in rainfall totals and cumulative impacts.
A developing surface low off the California/Mexico border will tap into the persistent conveyor belt of moisture from the subtropics and bring us our third system on Tuesday. It is going to trek near parallel the Bay Area Coast. This in conjunction with antecedent conditions has the potential to make this the most widespread impactful system. Notable features with this system include a negative tilt that's often a sign of an intensifying system and a 70 knot 925mb jet. There is still uncertainty in the location, strength, and timing of the feature, but confidence is increasing and the above still stands. As of now I would expect this to be the strongest windmaker. More tree impacts may be possible due to the non-dominant wind direction of southerly winds as compared to westerly winds. The reason is that trees build resiliency to their "normal" winds. Add in a strong wind from a non-dominant direction and loose soils and that increases the risk for downed trees, and thus downed power lines. The attendant cold front will sweep through on Wednesday bringing more rain and wind.
A digging surface low with upper-level support from the Washington/Canada border will bring our Christmas Day (Thursday) system. More rainfall and wind can be expected with this system. Hazardous beach conditions are also expected to return around this time, so make sure to exercise caution if near the water. This will not be the end of the rain, this is merely the end of the long term forecast. Wet conditions are expected through at least next Saturday. When all is said and done, locations can generally expect a December's worth of rain or a quarter of their annual averages, that's a lot of rain no matter how you slice it. If you are travelling by car for the Christmas holiday, I urge you to take the weather into account. Whatever you do, do not drive around barricades and remember turn around, don't drown!
(12z TAFS) Issued at 406 AM PST Fri Dec 19 2025
Mix of VFR to LIFR conditions across the board this morning. The TAFs remain complicated this morning as a weak cold front and light rain return today. Radar shows a few scattered showers this morning with the main rain band still located to our north along the Humboldt/Mendocino County border. This rain band will shift southwards into the Bay Area by late this morning, bringing a return of light rain to the region. Rain will take longer to reach the Central Coast with MRY and SNS not expecting rain until tomorrow night. Generally kept ceilings MVFR throughout much of the day but confidence is low to medium. CIGs drop to MVFR-IFR again tomorrow night with reductions in visibility expected as rain picks up in intensity.
Vicinity of SFO, MVFR conditions prevail for much of today with reductions in visibility possible as showers move over the airport. Low to moderate confidence that MVFR conditions will persist for much of the day. LAMP guidance indicates a brief period late morning where VFR conditions return but confidence is low that that will be the prevailing conditions. Showers reach SFO by mid-afternoon with more widespread rain reaching the airport by the late afternoon/early evening hours. Winds strengthen ahead of frontal passage (late afternoon/early evening) with gusts to around 20 knots expected.
SFO Bridge Approach, Similar to SFO.
Monterey Bay Terminals, Ceiling forecast for MRY and SNS remains challenging thanks to fog developing in the Salinas Valley (reducing visibilities at SNS) while VFR persists at MRY. LAMP guidance shows a brief period where decreased visibilities are possible at MRY this morning but this should be temporary with VFR conditions prevailing for much of the day. Ceilings lower and visibility decreases by tomorrow night as the cold front approaches the Central Coast and rain chances increase. Highest confidence in rain reach MRY and SNS after 09Z but guidance suggests it could arrive as early as 06Z.
(today through Wednesday) Issued at 315 AM PST Fri Dec 19 2025
A series of storm systems arrives today and continues through the extended forecast. Moderate winds continue into the weekend with occasional fresh gusts possible as a weak cold front moves through the coastal waters. The first system arrives Friday into Saturday with widespread light rain expected. Moderate to heavy rain is expected beginning Sunday and continues through at least mid next week as two stronger systems develop. Hazardous seas return early to mid next week as strong winds develop over the coastal waters.
Ca, None. PZ, Small Craft Advisory from 9 AM this morning to 3 PM PST this afternoon for Pt Arena to Pt Reyes 0-10 nm-Pt Arena to Pt Reyes 10-60 NM.
