Issued at 825 AM PST Wed Dec 17 2025
Forecast remains on track this morning with ongoing beneficial rainfall across the North Bay, Bay Area and East Bay. The highest rainfall totals since 2AM are in elevated portions of the North Bay which have received up to a quarter of an inch of rain, farther inland at lower elevations have seen under a tenth of an inch. The light rain should begin to taper off and shift east over the next few hours into the early afternoon. Thursday into early Friday should be mostly dry before rain chances pick up again across the North Bay by Friday afternoon and spread farther south into the weekend. The more impactful rainfall totals once again favor the North Bay beginning Saturday night through the remainder of the weekend. Coastal ranges along the Bay Area and remainder of the Central Coast will see higher amounts beginning late Sunday into Monday with lower lying areas looking at mostly beneficial rain with limited impacts.
, Issued at 304 AM PST Wed Dec 17 2025 (Today and tonight)
A cold front will bring beneficial, light rain showers to the region today. Most of the rain will fall in the morning with isolated to scattered rain showers possible in the afternoon. Higher terrain of the Bay Area can expect up to a quarter of an inch, the rest of the Bay Area can expect a few hundredths, and the Central Coast can expect drizzle at most. No adverse impacts are expected from this round of rainfall.
..issued at 304 AM PST Wed Dec 17 2025 (Thursday through Tuesday)
Pre-frontal rain showers are expected Thursday. Once again, rainfall will be beneficial and light with only up to a few hundredths expected for the Bay Area with the Central Coast remaining dry outside of some coastal/higher terrain drizzle. Widespread rainfall returns Friday. The culprit is a conveyor belt of moisture that is made possible by surface high pressure off the California/Mexico border and surface low pressure off the coast of British Columbia. The 80 member ensemble mean from the GEFS and ECMWF ensemble IVT forecast depict values near 500 kg/ms with a gradient to near 250 kg/ms for the Central Coast. A cold front will provide the dynamics necessary for precipitation and a corridor of increased winds. As of now, everything through Friday looks beneficial and generally unimpactful. We will have to monitor the evolution of the winds to see if they trend more impactful (45+ mph), but there is moderate to high confidence that the rain will be solely beneficial coming off of a three week dry spell. Preparations should be made by Thursday when it comes to making sure that gutters are cleaned out and loose outdoor items are secured. Uncertainty begins to creep in Saturday with some global ensemble members depicting that there may be a break in the rainfall. A contributing factor is likely that the deterministic ECMWF has a surface low developing and coming into Northern California while the GFS does not have this feature. The differences in the global models will have ramifications in the rest of the long term forecast and even beyond into the holiday. While seemingly little, this break will be consequential to the rest of the forecast. Global ensemble clusters are in agreement that heights will fall and widespread rainfall will return (if there is a break on Saturday at all) Sunday. This is the part of the forecast where impacts become more likely whether it be normal impacts from this type of system, cumulative impacts from the preceding rainfall, or holiday travel impacts. Rainfall is expected to increase in coverage and intensity through the day Sunday as the aforementioned conveyor belt of moisture gets reloaded and takes aim at the central part of the state. Additional hazards on Sunday will be wind and a slight (up to 20%) chance for thunderstorms. Rainy and windy conditions are expected to continue into Monday and Tuesday as the firehose of moisture slowly drifts north and then back south through the period. It's important to not get caught up in exact rainfall totals as they are guaranteed to change between now and the event; however, for context, San Francisco Downtown is expected to receive a month's (December average) worth of rainfall between now and Tuesday. HEFS gives less than a 5% chance of mainstem river flooding over the next 10 days. More than likely what will happen is minor/nuisance flooding in known problem areas like urban areas and flashy creeks/streams. I will reiterate that home outdoor preparations need to be made by Thursday. If you are travelling for the holiday like many of us are, please take into account the weather and plan accordingly by checking back with our forecast as well as the forecast of the National Weather Service for the area to which you are travelling to as well as the ones in between!
The Christmas holiday still remains outside of our official forecast period. Everything that was said above in terms of confidence and uncertainty apply here, even moreso. Global models continue their disagreement into the holiday with the ECMWF providing a wetter and more impactful solution by way of a longwave trough while the GFS has a drier and less impactful solution with a cutoff low meandering off of Point Conception. If rain happens immediately after the long term forecast, it is expected to be more of a Central Coast event than a North Bay event.
(18z TAFS) Issued at 825 AM PST Wed Dec 17 2025
A weak cold front continues to move across the Bay Area terminals at this hour and will begin to weaken/dissipate as it approaches the Monterey Bay terminals later this morning or early afternoon. As such, periodic reduced visibilities and LIFR-MVFR conditions will persist throughout the morning hours. Low ceilings will gradually clear from north to south by late morning and throughout the remainder of the afternoon. However, high clouds will persist. There is moderate confidence for low ceilings and reduced visibilities again tonight and into Thursday morning.
Vicinity of SFO, IFR to MVFR conditions persist this morning but will ceilings and visibilities will gradually lift and improve by late morning and furthermore into the afternoon. This will give way to VFR by mid-afternoon. Weak southerly winds will prevail ahead of the front and turn more northwesterly by early-to-mid afternoon. There is moderate confidence for low ceilings and reduced visibilities again tonight and into Thursday morning.
SFO Bridge Approach, Similar to SFO.
Monterey Bay Terminals, IFR to MVFR conditions persist this morning but will ceilings and visibilities will gradually lift and improve by late morning and furthermore into the afternoon. This will give way to VFR by mid-afternoon. Weak southerly winds will prevail ahead of the front and turn more northwesterly by early- to-mid afternoon. There is moderate confidence for low ceilings and reduced visibilities again tonight and into Thursday morning.
(today through Monday) Issued at 825 AM PST Wed Dec 17 2025
A cool front with light rain will move southward over the coastal waters and bays through this afternoon. However, light to moderate onshore breezes will prevail. Periodic wet weather continues through late week with additional rain arriving Saturday night through Sunday. Moderate seas will prevail through the week.
Ca, None. PZ, None.
