Issued at 652 PM PST Fri Dec 19 2025
The first push of rain has moved into the central Bay Area, and is now tapering off. While this was never going to be the main event, this first round over performed in the North Bay. Santa Rosa recorded 0.47" while a CALFIRE site in the coastal mountains near Sea Ranch received an impressive 2.79". As a result, the chance for river flooding has increased, particularly the small streams and creeks. Santa Rosa Creek surprised us by reaching action stage tonight. The larger rivers are still expected to remain in their banks, but the probability of flooding has increased here as well. The upper 10% peak exceedance probability would now bring moderate flooding to both the Russian River and Napa River. The 25% exceedance probability would bring minor flooding to the Russian, and put the Napa in action stage. Again the official deterministic forecast isn't explicitly calling for flooding of these large rivers yet, but the probabilities are creeping up. Rain intensity will ramp up Saturday afternoon and continue through the day Sunday. Again this next push will be focused on the North Bay, where a Flood Watch is in effect. The other update is to the wind forecast Tuesday-Wednesday. As the strong low pressure system develops and approaches the coast, a very strong low-level jet is likely to develop. This is a result of the strong pressure gradient force enhanced by the terrain effects of the coast-parallel SSE wind direction. Non-covective wind gusts along the coast are likely to reach 50 mph or more Tuesday night due to this effect.
, Issued at 406 PM PST Fri Dec 19 2025 (This evening through Sunday)
Light rain has been ongoing across the North Bay since earlier this morning with some of the higher elevation areas already seeing an inch of rain, and lower lying areas seeing mostly between 0.25"- 0.50" as of late afternoon today, which is a little ahead of current guidance. HiRes guidance indicates the moisture plume will gradually shift south toward the Bay Area tonight with mostly light scattered rain, also extending into the East Bay. By day break Saturday, light scattered rain, off-and-on in nature will persist through the morning hours over the same area. Much of the Central Coast will remain dry Saturday with the exception of the coastal ranges. The next wave of rainfall from the atmospheric river arrives once again along the coast of the North Bay and Bay Area late Saturday afternoon under embedded mid-level shortwaves and surface convergence from a quasi-stationary front draped across the North Bay. While that wave of precip moves over the northern half of our forecast area Saturday night into early Sunday, a developing but progressive trough begins to deepen to our north, pushing onshore into NorCal and Oregon by late Sunday afternoon.
The lift associated with the progressive trough axis pushing onshore during the day Sunday into early Monday morning will result in more widespread rainfall across our entire area, with the higher amounts still focused on the coastal ranges from Sonoma south to the Santa Cruz mountains looking at 2-3" over that same time period. Inland portions of the North Bay and Bay Area will see approximately 1-2" with locally higher amounts for higher elevations inland by early Monday morning. Farther south for the South Bay and remainder of the Central Coast are looking at between 0.5"-1.5" of rain with limited impacts for those areas. There is a slight chance of embedded sub- severe thunderstorms Sunday that may produce brief downpours and gusty winds up to 40mph.
A Flood Watch has been issued For the North Bay beginning Saturday afternoon at 4pm through Monday afternoon at 4pm. Flood concerns are relatively minor, centered around rivers, creeks and streams, that may rise out of their banks. Low-lying areas and flood prone areas may be impacted as well. Remember, turn around don't drown and never drive through standing or moving water.
..issued at 406 PM PST Fri Dec 19 2025 (Sunday night through next Friday)
By day break Monday, a deeper and broader midlevel trough forming to the west over open water will provide a partial reprieve from widespread rainfall as mid-level heights rise directly over our forecast area. The subtle rise in mid-level heights locally will interrupt some of the heavier rainfall rates and shift the atmospheric river from the Santa Cruz Mountains back to the north toward the Bay Area and North Bay. The buckling of the midlevel height fields to the west will represent the beginning of the most impactful portion of the forecast as strong surface cyclogenesis initiates offshore overnight Monday into Tuesday. By Tuesday afternoon a wide swath of strong winds will spread across our area (especially over our coastal waters from San Francisco south through Big Sur). Inland, winds will be gusty as well, up to 40mph at times for low lying areas and up to 60mph (or higher) across the highest inland peaks through early Wednesday morning. The strengthening low offshore will shift the fetch of the atmospheric river a little farther north with the North Bay once again looking to see the most rain in that time period, along with the Bay Area, with lesser amounts to the south over the Central Coast.
Unfortunately, a second rapidly deepening upper level low and its associated trough directly on the heels of the aforementioned strong system moving onshore Tuesday will absorb whats left of the atmospheric river and slam several strong trough axis' in rapid succession from the latter part of Wednesday through early Friday across most of the California coast line. The exact timing of the strongest winds and heaviest rain are too far out to get too specific at this point. However, plan on extensive travel delays Wednesday through Friday and exceptionally dangerous conditions along the coast line and in the near shore waters. Family and friends visiting the area will always be curious to be near the ocean while visiting our area. This will be no time to challenge the power of the atmosphere and the ocean. We've had numerous deaths recently up and down the Pacific Coast in our waters. No picture or memory is worth your life, just stay away for a majority of the extended forecast.
(06z TAFS) Issued at 926 PM PST Fri Dec 19 2025
Light rain band moving over the Bay Area will gradually weaken through tonight, providing a bit of a break in the rainfall before stronger, more widespread precip arrives Saturday afternoon. VCSH added for several sites ahead of the main rain band through parts of Saturday morning and midday. Best time of arrival for heavier, more persistent rainfall as it stands is just after the 00Z hour Saturday aft for North Bay terminals, spreading southward into the SF Bay Area by midday Sunday.
Vicinity of SFO, Pause in the rain overnight, but MVFR/IFR cigs persist as the atmospheric river moisture tap continues to advect through the region. As of this issuance, it appears the heaviest and most persistent rainfall will likely hold off until Sunday as much of the stronger upper level supports stays in the North Bay tonight and Saturday.
SFO Bridge Approach, Similar to SFO.
Monterey Bay Terminals, Mostly dry conditions further south through this weekend as the main moisture plume remains to the north. A couple of periods of VCSH both early Saturday morning and late evening. Heaviest rainfall will hold off until late Sunday.
(tonight through next Thursday) Issued at 652 PM PST Fri Dec 19 2025
A weak boundary is moving through the region with mainly light southerly winds over the waters. Generally light wind and seas are forecast through Saturday. By Sunday southerly winds may increase slightly ahead of another warm frontal boundary but wind and seas remain light overall despite periods of rain. A strong and more organized cold frontal passage will occur later Tuesday and the second half of next week with much stronger winds and building seas that will become very hazardous to mariners.
Ca, Flood Watch from Saturday afternoon through Monday afternoon for CAZ502>506.
PZ, None.
