textproduct: San Francisco Bay Area

KEY MESSAGES

Updated at 1209 PM PST Sat Dec 27 2025

- Calm, clear and cool conditions through mid week.

- King tides and rain chances arrive with the new year.

SHORT TERM

Issued at 1209 PM PST Sat Dec 27 2025 (This evening through Sunday)

We just flipped the radar back to clear air mode as the stormy weather is now firmly in the rear view mirror. High pressure has returned to the Eastern Pacific, bringing back our familiar northerly winds. This regime is bringing cooler and drier air. While the increased sunshine is keeping temperatures mild in the afternoon, enhanced radiational cooling with the long clear night will bring the coldest temperatures we've seen in a couple weeks Sunday morning. The interior Central Coast is under a Cold Weather Advisory, and the North Bay Valleys should get close to reaching the 36 degree threshold. The two limiting factors are high clouds streaming in from the North , and the current dew points in the mid 40s. The temperature can't drop below the dew point, so in order to get into the mid 30s, there will have to be robust fog formation to remove water vapor from the air and lower the dew point. Fog formation slows cooling in 2 ways. First the actual change of state from gas to liquid releases latent heat. Second the low level clouds block outgoing longwave radiation, limiting surface cooling. Don't be surprised to see Tule fog return as this set up seems perfect for it.

While the trough responsible for the Christmas storm is moving to the East, it will leave a small cut-off low over southern California. As this happens the EPAC ridge will build over the top, creating an inside slider pattern and supporting offshore winds early in the week. The SFO-WMC gradient is currently +2 mb, but should bottom out around -7 to -10 mb Sunday afternoon as the new pattern develops. This will reinforce the clear and dry conditions, while bringing the day time temperatures up a few degrees.

LONG TERM

Issued at 1209 PM PST Sat Dec 27 2025 (Sunday night through next Friday)

These offshore winds will continue Monday as the PWAT plummets below 0.3", or the bottom 10th percentile for this time of year. The same trend of cold foggy mornings with clear afternoons in the mid 50s will continue into Wednesday. The same cut-off low that caused the offshore winds will spend the first half of the week continuing to meander SW, well into the subtropical NE Pacific. By Wednesday it should get picked up by the next long wave trough, helping to amplify the pattern. This will bring uncommon southerly winds and tropical moisture to the area. It's almost monsoon like if it wasn't the end of December. The PW will climb well above 1" before the associated cold front barrels through on the 1st or 2nd. We'll likely get a good rain ahead of the front with showers in the post frontal cold air. There's obviously some timing details to work out, but the general pattern has a remarkable amount of confidence considering the complexity. The ensemble clusters all show some version of this unfolding.

AVIATION

(00Z TAFS) Issued at 345 PM PST Sat Dec 27 2025

Northerly surface to lower level winds in the Sacramento Valley are spilling into the Bay Area with e.g. surface winds recently NE 5-10 knots at KSFO and KOAK. Visible imagery shows SCT-BKN low clouds tracing out the NE wind flow into the Bay Area. The SAC-SFO pressure gradient is 0.4 mb. The larger scale WMC-SFO pressure gradient will steadily strengthen tonight through Sunday night resulting in additional offshore winds reaching the Bay Area.

A mainly clear sky will help with radiative cooling and patchy fog redevelopment tonight and Sunday morning. Will also have to monitor tule fog redevelopment in the Central Valley and the potential for a return of tule fog into the Bay Area, though at the time being the HRRR model shows greater tule fog development Sunday night into Monday. The offshore winds develop before then, tule fog development and transport of tule fog could start as soon as late tonight/Sunday morning due to recent rains and moistened boundary layer. KSTS and KAPC have fog in the TAFs with post sunset radiative cooling settling in, otherwise it's a moderate to high confidence VFR forecast for the remainder of the terminals.

Vicinity of SFO...VFR. Northeast winds 5-7 knots through tonight and Sunday.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...VFR. West-northwest winds near 10 knots until mid evening then shifting to east-southeast winds 5-10 knots and continuing into early-mid Sunday afternoon, then becoming light and variable to light onshore in the late afternoon.

MARINE

(Tonight through next Thursday) Issued at 326 PM PST Sat Dec 27 2025

Hazardous marine conditions will slowly decrease tonight due to northerly winds diminishing and rough seas abating. By tomorrow afternoon, moderate northerly breezes and moderate seas will prevail. High pressure and dry weather return for the weekend and early next week.

MTR WATCHES/WARNINGS/ADVISORIES

CA...Cold Weather Advisory from 2 AM to 9 AM PST Sunday for CAZ516>518-528.

PZ...Small Craft Advisory until 3 AM PST Sunday for Pt Arena to Pt Reyes 10-60 NM.