Issued at 859 AM PST Wed Dec 31 2025
Light rain is occurring across the coastal ranges, especially across the Santa Lucia Range and Santa Cruz Mountains with generally less than 0.05" of rainfall in the past 6 hours. Rain will increase in coverage throughout the day, yet amount are forecast to generally remain light. The ongoing forecast remains on track at this time with no updates anticipated this morning. The San Francisco tidal gauge reached 1.47 ft above normal (7.31 ft MLLW) at around 7:51 AM PST and is gradually lowering.
RGass
, Issued at 1229 AM PST Wed Dec 31 2025 (Today and tonight)
We switched KMUX to precip mode as rain and/or virga moving in from the south is coming in range. Most of this activity is over the coastal waters, and the lowest radar scan can only see 7,000 feet at this range. Unfortunately there aren't any buoys or ships capable or willing to report if anything is reaching the surface. Based on the 00Z sounding, most of these rain drops will evaporate in the well defined dry layer below 800 mb where the average relative humidity is less than 15%. Of course the evaporation itself raises the humidity and makes it easier for subsequent drops to make it further down. The moistening process will continue through the morning, priming the lower atmosphere for more efficient rain as the day progresses.
The overall pattern is driven by a vertically stacked cut-off low roughly 500 miles west of the Channel Islands. The eastern periphery of this feature is pumping a large area of southerly winds and associated moisture from the deep tropics. This low will catch the next ride NE on an the upstream portion of an approaching long wave trough moving across the Eastern Pacific. This upper level pattern will also provide divergence aloft, removing weight from above the surface low, thus decreasing the surface pressure and providing some moderate cyclogenesis as the feature moves towards the Bay Area. We should pick up between 0.5-1.0" of rain over the next 24 hours as a warm up for the rest of the week. Will it rain for NYE celebrations? Probably, yes. In the Bay Area a rain jacket or umbrella should do just fine in the steady light rain and gentle wind expected up till midnight. If you're celebrating on the Central Coast, it may be a little heavier in the last hour or two of the year.
..issued at 1229 AM PST Wed Dec 31 2025 (Thursday through Tuesday)
The warm, moist southerly winds with an approaching, deepening low pressure system to our west means we should get a somewhat uncommon warm frontal passage Thursday. Antecedent warm moist air with increasing kinematics support as the front approaches should support some stronger convection and possibly trigger some thunderstorms as the front passes. This threat will be greatest if the triple point (where the occlusion, cold front, and warm front meet) moves over land. The Central Coast has the best chance for thunderstorms. The thermodynamics don't look great until midday on Thursday, but if the timing lines up with frontal passage, it could get interesting. A NAM point sounding at Salinas shows the FROPA timing will be very close to the instability window opening around noon. Otherwise the afternoon of New Years Day should just bring scattered showers as opposed to the more widespread rain on NYE.
After the low makes landfall Thursday, a more typical atmospheric river set-up will takes shape for Friday. A deep trough over the Eastern Pacific will bring strong SW flow to the California, with a ribbon of moisture pointed somewhere between the North Bay and Southern California. The high moisture anomaly near Baja never really clears out, and will push north again, reinforcing this round of rain. This should be the wettest and windiest day of the week, with bigger impacts bleeding into Saturday morning. Southerly winds will likely gust into the 50 mph range along the coast and in higher terrain just ahead of the cold frontal passage. Conditions will improve behind the front, but scattered showers will continue through the weekend, with 0.5-1.0" expected each day from Saturday through Monday. A new low pressure system and associated cold front is possible Monday or Tuesday. The ensemble clusters have differing opinions on the strength and timing of this feature, but they all show a trough off the coast, which is enough to keep rain chances around through the entire 7-day forecast period. KMUX will stay in precip mode for the foreseeable future.
(12z TAFS) Issued at 454 AM PST Wed Dec 31 2025
Light to moderate winds are expected through the TAF period as a cut- off low moves into the area. Expect mostly light showers to build through the day with some pauses in rain chances over the evening, but shower activity looks to be fairly persistent. Cloud cover will most stick to the upper levels and mid-levels through the TAF period, but some sights may see very brief MVFR-level clouds. Shower activity continues well beyond the TAF period with breezy southerly winds building into Thursday.
Vicinity of SFO, Light showers are entering the area, but won't be impactful until the afternoon, by causing slight reductions in visibilities. Expect mostly light easterly winds through the morning before winds become more variable and affected by more localized effects into the afternoon and through the night. Shower activity lasts through the end of the TAF period, with winds turning more southerly and then becoming stronger slightly after the TAF period.
SFO Bridge Approach, Similar to SFO.
Monterey Bay Terminals, Light showers are building into the area. Expect mostly light to moderate winds through the day. Winds at SNS will stay mostly southeasterly while MRY becomes more variable into the afternoon. Showers will offer slight reductions in visibilities through the TAF period. Winds turn southerly at MRY into the night as southeast winds build at SNS and become breezy.
(today through Monday) Issued at 859 AM PST Wed Dec 31 2025
Moderate to fresh winds and moderate seas continue into Thursday. Widespread light rain and a low potential for thunderstorms across the southern waters continues into Thursday. Winds rapidly strengthen from strong to gale force by early Friday as a second, stronger, system arrives. Periods of moderate to heavy rain and a slight potential for thunderstorms are expected Friday into Saturday. Winds diminish early Sunday but breezy conditions and rain showers continue into next week.
Issued at 859 AM PST Wed Dec 31 2025
Perigean spring tides (King Tides) will impact the region through Sunday. This is due to the combination of the full moon on 1/3, lunar perigee on 1/1, and perihelion on 1/3. In other words all three planetary bodies are lined up and close to each other. In addition to the high astronomical tide, the incoming low pressure system will bring strong southerly winds, generating some storm surge. The combination of these factors will bring minor to moderate coastal flooding to the low-lying areas near shorelines and tidal waterways during high tide through Sunday. At the San Francisco tidal gauge, high tide is expected to be 2.0 ft above normal at 8:41 AM Thursday, 2.2 ft above normal at 9:34 AM Friday, 2.2 ft above normal at 10:26 AM Saturday, and 1.8 ft above normal at 11:18 AM Sunday. These predictions include up to 1 foot of storm surge that will enhance the astronomical tide and flooding threat. High tide varies up to 90 minutes earlier or later along the Pacific Coast and through the San Francisco Bay, respectively.
Ca, Coastal Flood Advisory until 2 PM PST Sunday for CAZ006-505-506- 508-509-529-530.
PZ, Small Craft Advisory from 9 PM Thursday to 3 AM PST Friday for Pt Arena to Pt Reyes 0-10 nm-Pt Arena to Pt Reyes 10-60 NM.
Gale Warning from 3 AM to 9 AM PST Friday for 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.
Small Craft Advisory from 3 AM to 3 PM PST Thursday for Pigeon Pt to Pt Pinos 0-10 nm.
Gale Warning from 9 PM this evening to 3 PM PST Thursday for Pt Pinos to Pt Piedras Blancas 0-10 nm.
Small Craft Advisory from 9 PM this evening to 3 PM PST Thursday for Pigeon Pt to Pt Pinos 10-60 NM.
Small Craft Advisory from 3 AM to 9 AM PST Friday for Pigeon Pt to Pt Pinos 10-60 NM.
