Issued at 545 PM PST Sat Dec 20 2025
We're seeing a slight lull in the rain this evening, but don't let that fool you. The short term forecast remains confident and very wet through Sunday night. The 00Z balloon measured the precipitable water at 1.46". Not only is that a daily record, it's in the top 10 of all December observations going back to 1948. So the atmosphere is primed and ready for the next round of rain. There won't be much lost to evaporation on the way down. Both the GEFS and ECMWF ensembles show a 95%+ chance of at least AR3 conditions, with around a 40-50% chance of reaching AR4 conditions on the CW3E Atmospheric River Scale. This first push will end sharply Monday morning. We're still expecting some rain Monday, but much less than Sunday. The next pulse arrives Tuesday, but the rain totals are looking less impressive as JM mentioned in the long term section. Using the same AR scale, there is only a 30-40% chance of reaching AR3 conditions from Tuesday through Thursday. Bottom line, there is an increasing chance that the wettest day will be tomorrow for most of the Bay Area, and especially in the North Bay. The same is not true for the Central Coast, which will get progressively wetter as the week goes on.
, Issued at 346 PM PST Sat Dec 20 2025 (This evening through Sunday)
The atmospheric river moisture plume continues to oscillate this afternoon, the focus has been on the Bay Area since mid-morning and will then gradually move back toward the North Bay tonight into early tomorrow morning. After sunrise Sunday, we'll see a notable shift south toward the Central Coast as the upper level trough associated with the strengthening system in the Gulf of Alaska deepens. The twenty-four hour rainfall totals in the North Bay are ahead of pace, with the Flood Watch beginning this afternoon and periods of moderate to heavy rainfall expected overnight within the area covered by the watch.
Satellite imagery this afternoon shows a large cloud shield extending from Monterey Bay well north into southern Oregon. The combination of a surface trough shifting south from NorCal to the Santa Cruz mountains by late Sunday, a fully saturated boundary layer up to 850mb and continuous shortwave energy embedded in the 500mb flow will result in rainfall totals across the North Bay around 2-3" in the valleys and other low-lying areas, with higher elevations potentially seeing up to 6" or more locally. The Mark West Creek Near Mirabel Heights is forecast to reach action stage by late Sunday evening, travelers should be cautious driving through through the North Bay for the remainder of the extended forecast.
..issued at 346 PM PST Sat Dec 20 2025 (Sunday night through next Friday)
Monday offers a bit of a reprieve for the North Bay as the atmospheric river moisture plume is once again pushed south toward the Santa Cruz Mountains and the remainder of the Central Coast. The deepening and expanding upper low moving south out of the Gulf of Alaska begins to assert its influence over the synoptic pattern at our latitude. As the atmosphere resets to the west over open water we'll still see scattered light rain across most of our area during the day Monday with minimal impacts.
By Tuesday, some uncertainty is introduced into the forecast. The most recent guidance suggest a less dynamic surface response to the deepening trough off the coast, especially early on. Previous guidance indicated rapid surface pressure falls during the day Tuesday, with the strong area of low pressure taking aim at the Bay Area/North Bay by late Tuesday night. Tuesday into Wednesday is now in the later time frame of higher resolution data as well, with the NAM12 indicating a less organized response at the surface over that same time frame as well. Deterministic guidance depicts a more organized surface response later in the forecast period and farther north off the coast of NorCal by late Wednesday night. The differences are somewhat subtle and confidence for impactful rainfall across the North Bay between now and the end of the week remains very high.
For the most part all the ensemble members have begun to pick up on the subtle changes in the surface response and pattern. While some of the inland rainfall totals may come down somewhat as we move through the week, the pattern remains wet throughout our entire forecast area and travel impacts will persist, especially the farther north you are. Storm force to near hurricane force winds at times up and down our coast Tuesday through early Friday will continue to produce exceptionally dangerous conditions along our coastal beaches and coastal waters.
(06z TAFS) Issued at 857 PM PST Sat Dec 20 2025
Current radar showing scattered light rain showers mostly confined to the North Bay. This placement will continue while the intensity of the precip will trend upwards through tonight. Plume of moisture and associated moderate rainfall will migrate southward Sunday afternoon around the 00Z hour, beginning to impact Bay Area terminals through Sunday night. Gusty S winds will also accompany the front as it slowly moves south through the region. Outside of rainfall concerns, MVFR/IFR cigs will prevail through the TAF period.
Vicinity of SFO, Mostly dry overnight and early Sunday as the main moisture plume stays north of the SF Bay. This begins to change Sunday afternoon as the plume drifts southward, taking aim at the Bay Area around the 00Z hour. Preceding the precip, gusty S winds will develop overnight tonight as the storm system strengthens. These gusty S winds will continue through much of the period until the front passes late Sunday night.
SFO Bridge Approach, Similar to SFO.
Monterey Bay Terminals, Moisture begins to increase tonight ahead of heavier rainfall later in the period. Gusty S winds anticipated by mid-morning Sunday, lasting through the rest of the period. Pretty much keeping VCSH through the period due to terrain enhancement of isolated showers, but heavier, more persistent rain will likely hold off until just after the current TAF period (Sunday night).
(tonight through next Friday) Issued at 857 PM PST Sat Dec 20 2025
Unsettled weather prevails through the next several days. Rainfall intensity increasing tonight and Sunday across the northern waters with a strong cold front sagging southward to near Pigeon Point by Sunday evening. Gusty southerly winds increase along the front through Sunday 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.
Ca, Flood Watch through Monday afternoon for CAZ502>506.
PZ, Small Craft Advisory until 9 PM PST Sunday for Pt Arena to Pt Reyes 0-10 nm-Pt Arena to Pt Reyes 10-60 NM-Pt Reyes to Pigeon Pt 0-10 nm-SF Bay N of Bay Bridge.
Small Craft Advisory from 9 AM to 9 PM PST Sunday for Mry Bay-Pt Pinos to Pt Piedras Blancas 0-10 nm.
Small Craft Advisory from 3 AM to 9 PM PST Sunday for Pigeon Pt to Pt Pinos 0-10 nm-Pigeon Pt to Pt Pinos 10-60 NM.
