Active Weather System to Deliver Rain to the Bay Area
A wet and windy weather system is moving into the San Francisco Bay Area, bringing much-needed precipitation and a sharp drop in temperatures. Local residents should prepare for slick morning commutes, gusty coastal winds, and rapid shifts in our regional microclimates over the next forty-eight hours. This incoming front marks a temporary end to our recent dry spell, ushering in a classic late-season unsettled pattern.
Timing and Expectations for the Wet Weather
The low-pressure system is tracking south from the Gulf of Alaska, carrying a plume of cold moisture directly toward northern California. Light showers will begin along the Sonoma and Marin county coasts by early Thursday morning before intensifying into a steady, widespread rain. The main cold front is expected to sweep through the central Bay Area during the afternoon commute, making driving conditions hazardous along major corridors like Interstate 80 and Highway 101.
By Thursday evening, the core of the system will push into the East Bay and South Bay valleys. While this is not an atmospheric river, it will deliver consistent, moderate rainfall capable of causing minor localized ponding on roadways and in poorly drained urban areas. Showers will linger into Friday morning, gradually tapering off from north to south by Friday afternoon as the storm system exits the region.
Projected Rainfall Totals by Sub-Region
Precipitation amounts will vary significantly due to the Bay Area’s unique topography. Coastal mountains, particularly the King Range and the Santa Cruz Mountains, could see up to 1.5 inches of rain. Most urban flatlands, including San Francisco, Oakland, and San Jose, will likely average between 0.5 and 0.75 inches. Rain-shadowed valleys in the far East Bay and Tri-Valley areas will see the lowest totals, generally hovering around 0.25 inches.
Microclimate Impacts and Wind Advisories
Along with the rain, the National Weather Service has issued a wind advisory for coastal areas and elevated ridges. South-to-southwest winds will increase Thursday morning, peaking at 25 to 35 mph, with isolated gusts up to 45 mph along the immediate coast and atop Mount Diablo and Mount Tamalpais. These winds could knock down weak tree limbs and cause isolated power outages, especially where soils become saturated.
Temperatures will also take a noticeable dive across all microclimates. Daytime highs that recently reached the low 70s will struggle to top 55 degrees on Thursday and Friday. Overnight lows will drop into the 40s near the bay, while inland valleys could see temperatures plummet into the mid-30s once skies clear, raising the potential for late-season frost.
The table below summarizes the expected conditions across the major Bay Area microclimates during the peak of the storm on Thursday.
| Region | Expected Rainfall | Peak Wind Gusts | Daytime Highs |
|---|---|---|---|
| North Bay Valleys | 0.75 – 1.25 inches | 30 mph | 54°F |
| San Francisco & Peninsula | 0.50 – 0.75 inches | 40 mph | 55°F |
| East Bay Inland | 0.25 – 0.50 inches | 25 mph | 56°F |
| Santa Cruz Mountains | 1.00 – 1.50 inches | 45 mph | 52°F |
What to Watch Next: Clearing Skies and Cold Nights
As the cold front moves east toward the Sierra Nevada, high pressure will rapidly build over the Pacific. This transition will usher in dry, cool air from the north, clearing out the cloud cover by Friday night. The combination of clear skies, dry air, and light winds will set the stage for strong radiational cooling, leading to the coldest night of the week.
Saturday and Sunday will bring plenty of sunshine, but temperatures will remain brisk. Highs will hover in the upper 50s to low 60s, which is slightly below average for this time of year. Northerly breezes will persist, keeping a chill in the air for outdoor weekend activities. Meanwhile, mountain travelers should prepare for significant winter weather conditions, as this same storm system is forecast to drop over a foot of fresh snow across the Sierra passes.
Frequently Asked Questions
- Will this storm cause major flooding in the Bay Area?
No major widespread flooding is expected. However, minor localized street flooding and ponding in low-lying areas are highly likely during the peak rainfall on Thursday afternoon. - How will this system affect travel to the Sierra Nevada?
Sierra travel will be highly hazardous on Thursday and Friday. Heavy snow and strong winds will likely trigger chain controls and significant delays on Interstate 80 and Highway 50. - When will temperatures start to warm back up?
A gradual warming trend will begin on Monday. Temperatures are expected to return to seasonal averages in the mid-to-upper 60s by the middle of next week as the high-pressure system strengthens. - Should I protect my outdoor plants from frost this weekend?
Yes, residents in the coldest inland valleys of Sonoma, Napa, and Santa Clara counties should cover sensitive outdoor plants on Friday and Saturday nights when temperatures could drop to the mid-30s.
To stay safe during this weather transition, clean out your gutters before the rain starts, secure loose outdoor patio furniture against strong wind gusts, and allow extra travel time for your Thursday evening commute.
Active Weather System to Deliver Rain to the Bay Area
