California will get rain this week; storm outlook for SF, state

Pedestrians use umbrellas and rain jackets to shelter from the rain in San Francisco as a storm passes through the Bay Area on Nov. 5. Rain is expected to return to the region this week after a nearly four-week dry spell. 

Lea Suzuki/S.F. Chronicle

After nearly four weeks without rain, Californians are finally seeing precipitation return to the forecast. The wet pattern arriving this week comes in pieces, and the Bay Area should see significant rain from the final storm, while temperatures will remain cool.

Here’s how the week shapes up, storm by storm.

Storm 1: Rain for the North Coast only

The first system arrives Monday evening, but its impacts will be limited to California’s far North Coast in Humboldt and Del Norte counties. It’s welcome news for Eureka, where just 0.11 inches of rain has fallen in December, nearly 3.5 inches below normal.  

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A cold front tied to a distant low pressure system near British Columbia will bring periods of light to moderate rain from Monday afternoon through Tuesday morning to places like Eureka, Crescent City and the Siskiyou Mountains. 

Monday’s system is the weakest of the bunch this week and will just bring meaningful precipitation to the northern California coast.

Baron/Lynx

Beyond that, this initial storm won’t be felt anywhere else in the state. Without stronger support from a closer in proximity parent low pressure system, the cold front will fall apart early Tuesday morning. As a result, measurable rain will not reach the Bay Area, and most locations south of Mendocino County will stay dry.

Storm 2: Just enough to break the dry streak

The next chance at precipitation arrives quickly on the heels of the first, with rain redeveloping along the North Coast by Tuesday afternoon and evening. This cold front will be stronger and more efficiently tapped into moisture from the Pacific, and will push farther south along the California coast. All of that adds up to a more impactful rainfall event. 

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Light rain will spread into Mendocino County, the northern Sacramento Valley and the Sierra foothills late Tuesday, most likely after sunset, and persist overnight. Meanwhile, after midnight Wednesday, light to moderate rain will reach the North Bay, particularly along the Highway 101 corridor.

Light rain showers will spread into San Francisco, Oakland and along the Peninsula in the predawn hours Wednesday. That should make for a slightly wet early morning commute Wednesday morning.

Rainfall should reach the Bay Area on Wednesday morning, but totals will be very low.

Baron/Lynx

Despite having a more widespread impact, Wednesday’s storm system will be weakening as it moves south through California, keeping rainfall totals modest. By the time the rain ends Wednesday morning, upward of 0.25 inches of rain will have fallen in the North Bay along the Highway 101 corridor, while most areas south of the Golden Gate are likely to see no more than a tenth of an inch. That’s enough to technically end the dry streak, but otherwise not impactful at all.  

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Unfortunately, neither of the first two storm systems will provide much relief for the snow-starved Sierra Nevada. Snow levels for both systems will remain high, hovering near 8,000 feet, meaning precipitation will fall as rain at most Sierra ski resorts. Only the highest elevations are likely to see light snowfall.

Storm 3: The one worth watching

The third storm system, expected to arrive late Friday into early Saturday, offers the best chance for meaningful rain across the Bay Area and a more favorable setup for snowfall in the Sierra.

By the end of the week, the jet stream is forecast to tighten and align more directly from west to east across the Pacific, a configuration that favors cold fronts holding together as they move into California. That jet will also tap into a plume of subtropical moisture, and a surface low pressure system is expected to develop off the Northern California coast, helping to generate more substantial precipitation as it moves inland and southward.

The storm system at the end of the week will have the benefit of tapping into an atmospheric river pointed more toward the Bay Area. 

Baron/Lynx

Rain is likely to spread into the North Coast late Thursday night, then expand southward through the North Bay on Friday morning. Steadier rain should reach San Francisco, the East Bay and the South Bay by Friday afternoon and evening.

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It’s still too early to lock in exact totals, and the exact timing of the rain is likely to change a bit as we get closer. But this system has the highest precipitation potential of the week. North Bay valleys could see between a half-inch and 1.5 inches of rain, with closer to a half-inch possible in San Francisco and Oakland and lower totals farther south.

This system also brings the best snow prospects the Sierra has seen in weeks. Snow levels are expected to drop compared to earlier storms, potentially falling to around 6,000 feet by Friday night. While the system will move through relatively quickly, a few inches of snow could fall at lower elevations by Saturday, offering a much-needed boost for ski resorts.

Once the storm exits early Saturday, conditions should dry out quickly. 

Each one of these systems helps to open the door a bit more for more rain and snow chances for California beyond next weekend. An active pattern looks likely to continue into Christmas week, though at this point the signal favors progressive storms and moderate rainfall rather than prolonged or extreme events.

Monday Bay Area breakdown:

San Francisco:Monday will start out with mostly cloudy skies across the city. The low clouds should break up by the late morning and early afternoon, leaving some high-altitude (above 25,000 feet) clouds and partial sunshine for the rest of the day. Temperatures will be a bit warmer than Sunday, with afternoon highs in the low to mid-50s. Low clouds and fog return overnight with lows in the upper 40s to low 50s. 

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North Bay:Monday is likely to end up mostly cloudy across the North Bay, especially along the immediate coast. A few breaks of sunshine are possible along Highway 101 in the afternoon, but it won’t help with the cool temperatures. Highs will be in the upper 40s in Vallejo and Vacaville and in the mid-50s in Novato and Santa Rosa. Clouds and fog return overnight, with lows ranging from the upper 40s to low 50s. 

East Bay:Morning clouds will give way to partial sunshine by the afternoon, especially from Richmond down to Fremont, where highs will be in the upper 50s to around 60 degrees. The clouds will linger a bit longer in the Tri-Valley and Livermore Valley, but sunshine should pop out there as well, with highs in the mid-50s. In Northern Contra Costa County, Walnut Creek and Concord will remain overcast for much of the day, with highs in the upper 40s. Clouds return for most spots overnight, with lows in the upper 40s to low 50s. 

Peninsula:Low clouds and fog will cover the Highway 101 stretch on Monday morning. Skies will gradually clear as the day progresses but will never be completely cloud-free. Temperatures will be pretty uniform along the Peninsula, with highs in the upper 50s from South San Francisco down to Redwood City. Clouds will return overnight, and temperatures will be mild, with lows right around 50 degrees. 

South Bay:Low clouds will hang across the South Bay through much of Monday morning. Partly sunny skies will develop by the afternoon, with mild temperatures. Highs will generally be in the upper 50s to low 60s. Low clouds return overnight, but conditions remain stay mild, with lows about 50 degrees.