The low-pressure system that brought dark clouds and northwest winds to the coast last night is now hovering over Northern California. It's set to raise winds and rounds of rain into the Bay Area today before departing for Oregon. Dry conditions will then briefly return for the first half of the weekend but the break from the rain will eventually be stomped out by a second low-pressure system.
This system will follow the path left behind by today's rainmaker, hoisting rain and snow showers across Northern California by Saturday night and into Sunday. All in all, this weekend is shaping up to be a mixed bag of weather conditions for residents across the Golden State.
When will today's rains let up?
For residents waking up after 9 a.m. Friday morning, the good news is that the bulk of moderate rain showers will already be halfway to the Sierra Nevada.
That's because the cold front out ahead of the low-pressure system is forecast to roll into the Bay Area between 2 and 6 a.m. Friday'scold front will carry the majority of the moderate rain showers slated for San Francisco, Oakland, San Rafael and the rest of San Francisco Bay.
Unfortunately, that means morning commuters coming into San Francisco from the Santa Clara Valley, East Bay hills, Peninsula and North Bay valleys will be contending with slippery roadways from these moderate rain showers right around the peak of the morning rush hour. The same goes for muni and BART riders who may come across delays if some of these showers briefly stall over San Francisco and Oakland.
Thankfully, weather models — including the North American weather model that often forecasts higher rainfalls in its simulations for the Bay Area than what actually plays out – are leaning toward a scenario where the cold front quickly exits the Bay Area after 9 a.m.
The rest of the morning looks to be mostly a shower-fest for the San Francisco Peninsula, East Bay hills, Marin County and Sonoma County coastline and the 101 corridor east from Morgan Hill to Gilroy. Look for spotty showers across most of the Bay Area through 1 p.m. before they all slowly fizzle away Friday afternoon.
All the extra clouds overhead tonight will also help to trap heat from earlier in the day, keeping nighttime lows on the warmer side. So, expect a comfortable, cloudy night across most of the Bay Area with temperatures in the upper 40s and lower 50s.
Is there still another chance for rain this weekend?
After a brief break from the rain, a second low-pressure system will roll into Northern California by noon on Saturday. This system will have a bit more of a kick to it, churning up 25 to 35 mph gusts across most of San Francisco and the wider Bay Area on Saturday afternoon.
These steadfast winds will be accompanied by light to moderate rain showers through Sunday evening, with the heaviest showers slated for late Saturday night into early Sunday morning.
Will there be an elevated risk for flooding like last month?
These rain showers are forecast to raise rainfall totals between an inch to an inch and a half of rain across most bayside cities.Higher peaks in the hillsides and mountains will get closer to 2 inches, while the mountains in the North Bay and in San Mateo and Santa Cruz counties could get as much as 3 inches of rain before all is said and done.
Thankfully, this rainfall will be scattered over the course of three days, rather than the three hours seen at the height of the New Year's Eve storm in San Francisco. But, given that the soils are still saturated from January's deluge, it's important to practice safe driving on slippery roadways and to stay alert for landslides in more rural areas.
• San Francisco: A low-pressure system will set up shop over San Francisco Bay Friday morning and usher rounds of moderate rain to Sutro Tower, Bernal Heights, Mount Davidson and a few other hillsides by West Portal. Brief downpours will be possible on the west side through 9 a.m. as showers darken the skies over the Sunset and Richmond districts. Some of these moderate showers will eventually stream east of Sutro Tower and into the Castro, downtown and SoMa between 8 a.m. and 11 a.m. before trailing into San Francisco Bay. Brief showers will then be possible through 3 p.m. across the city before they eventually fizzle away. Look for daytime highs on Friday that will peak in the lower 60s between Muni's lines from West Portal to the Embarcadero, while commuters heading down to Glen Park and Sunnydale this afternoon will be in for highs in the upper 50s.
The dry weather will hang around through noon on Sunday before the next round of rain showers streams into the city. Have a raincoat or umbrella handy for Saturday and Sunday because these showers will last all the way through Sunday afternoon. Look for daytime highs in the lower 60s on Saturday before winds and showers pick up in the evening. Some of the windiest spots will develop overnight and into Sunday morning along the water and bays, reaching 35 mph in Ocean Beach, the Presidio, Embarcadero and Hunter's Point. By Sunday afternoon, these showers and winds will drop off and make way for a chilly, cloudy day with highs in the mid-50s.
• Pacific Coast and Peninsula: Rounds of showers will begin streaming into the coastline today and through the evening as highs reach the upper 50s region-wide. Light to moderate rainbands will impact most of Highway 1 between Half Moon Bay and Pacifica as winds pick up to 30 mph this afternoon. Brief, heavy bands of rain will be possible in the San Bruno Gap but expect most showers to be light and moderate through 4 p.m. this afternoon. BART riders at San Francisco International Airport and Daly City will likely come across a wet morning and evening commute home before showers finally leave the Peninsula this evening.
The dry weather tonight and into Saturday morning will help clear out slippery conditions on Highway 92 between Half Moon Bay and San Mateo, but expect those conditions to come back by Saturday afternoon as 25 to 30 mph bring showers back to the Peninsula. Look for daytime highs in the lower 60s on Friday along Highway 1 while upper 50s will be found in Daly City, South San Francisco and Millbrae.
All the clouds from Saturday afternoon's showers will keep nighttime lows in the lower 50s on the coast, while cities along the 101 corridor south of Millbrae are likely to fall to the upper 40s Saturday night and into Sunday morning thanks to breaks in the clouds. Expect bursts of moderate rain to spread to the San Bruno Gap and most of Highway 1 from 11 p.m. on Saturday through Sunday morning.
Showers will fizzle away across the Peninsula by Sunday afternoon, leaving behind a trail of cool air that will keep Sunday's highs in the mid-50s.
• North Bay: Residents in the Petaluma, Santa Rosa and Napa valleys — along with some of the summits in the Marin headlands — will be waking up to the sound of rain this morning. These showers will peak right around 6 a.m. before slowly breaking apart through Friday afternoon. Watch for slippery roadways if you plan on traveling along Highways 101, 29 and 17 this morning. Look for clearer skies and highs in the upper 50s by 3 p.m. as conditions improve.
This break in the weekend rain-fest will continue until noon on Saturday, when skies will darken as the next round of rain showers sweep onto the Sonoma County and Marin County coastline. Light to moderate showers will spread east on Saturday evening, keeping temperatures in the mid-50s as they once again bring slippery conditions to roadways across the region.Patches of Napa and Sonoma counties, including Healdsburg and Guerneville, will experience moderate to heavy rainfall tonight and into early Sunday morning, but these rains will quickly weaken by dawn and turn to light showers over the course of the day on Sunday.
Expect Saturday afternoon and Sunday afternoon to be socked in with light showers all across the North Bay, including San Pablo Bay, the delta, the banana belt along 101 from Novato to San Rafael and cities along Highways 37, 80 and 780 in Solano County. Most of these showers will clear by 1 p.m. on Sunday and make way for a cloudy evening with temperatures in the low to mid-50s.Residents along the Marin Headlands and Sonoma coast will be the last to clear out from the rain on Sunday, with light showers persisting through 5 p.m.
• East Bay: The pitter-patter sounds of rain will make their way into all corners of the East Bay Friday morning, with Alameda Island, the Oakland and Berkeley hills and valleys near the Caldecott Tunnel seeing some of the heaviest showers. Most East Bay residents along the I-80/I-880 corridors will get a taste of moderate rain showers before they taper off around 1 p.m.
Some of these rain showers will survive into Friday afternoon, keeping most of the I-680 corridor rain-soaked until 4 p.m. Daytime highs across Alameda and Contra Costa counties will recover from the cloudy and rainy morning and rise to the upper 50s to lower 60s. By Saturday afternoon, temperatures will reach the upper 50s before skies become overcast again. Another round of showers will break through the Oakland and Berkeley hills. Look for more widespread showers along San Francisco Bay by Saturday evening and eventually in interior cities like Concord, Walnut Creek and the San Ramon and Livermore by Saturday night.
Low-lying areas in Oakland, Fremont, Hayward and Richmond will see their lion's share of ponding and minor urban flooding, but these weather hazards will subside by Sunday morning as showers weaken. There is a slight risk of damage to loose objects from these showers as northwest winds — reaching gusts to 30 mph —spread into the region during the overnight hours. These winds will largely drop off by Sunday afternoon as rain fizzles away and makes way for a cloudy, chilly Sunday with highs in the mid-50s.
• South Bay and Santa Cruz: A rainy start to Friday is on tap for the Santa Clara Valley and the Santa Cruz Mountains. Light sprinkles from a low-pressure system will soak most of the South Bay and Central Coast today and then again on Saturday afternoon through Sunday morning. Rainfall totals in San Jose, Milpitas and Sunnyvale, and coastal areas of Santa Cruz, Aptos and Capitola are expected to reach an inch and a half. Residents in the Santa Cruz Mountains will likely see higher totals— up to 3 inches of rain — before all is said and done.
Thankfully, these rainfall totals will be scattered out over the course of 3 days, keeping flood risks low. Residents along the highway 101 and 17 corridors will see slippery conditions on Friday morning and then again Saturday night into Sunday morning as the two rounds of rain stream over the region.
Look for daytime highs on Friday and Saturday in the upper 50s to lower 60s. Some of the warmest spots will be in the wind-sheltered Santa Clara Valley where San Jose, Los Gatos and Morgan Hill will likely climb to the mid-60s once again. But it all goes downhill by Sunday as cold air from this weekend's low-pressure system drops temperatures by 7 to 10 degrees in the valley, keeping daytime highs in the mid-50s.
Gerry Díaz (he/they) is a San Francisco Chronicle newsroom meteorologist. Email: [email protected] Twitter @geravitywave
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The Bay Area’s first round of rain is here. Here’s a look at what this weekend’s one-two punch of low-pressure systems has in store have 2559 words, post on www.sfchronicle.com at February 3, 2023. This is cached page on USA Posts. If you want remove this page, please contact us.