Bay Area storm watch: atmospheric river is here, what to expect

After a record-breaking winter with storm after storm pounding through the Bay Area, the latest 'atmospheric river' has arrived.

A significant storm hit the region Thursday and continued Friday with strong winds and heavy rainfall. Flooding will occur from Thursday afternoon until Sunday morning, according to the National Weather Service. 

There was heavy rain on Thursday afternoon and evening, and an even more intense downpour occurred overnight into early Friday morning. 

Several inches of rain are likely to fall by Saturday. The South Bay could see 2 to 3 inches of precipitation while the coastal hills of the North Bay may get 5 to 6 inches. The Santa Cruz mountains may receive up to 7 inches of rain.

On Thursday, Gov. Newsom requested a Presidential Emergency Declaration to support storm responses and rescue efforts. Newsom makes the move after several severe storms continue to batter the state.

A day earlier, Newsom declared a state of emergency for Napa, San Francisco, San Mateo and Santa Clara counties. The declaration covers 17 other California counties that also may get hit hard by the storm.

If federal assistance is provided, additional equipment and more personnel are expected to arrive in the state.

At higher elevations in the Sierra Nevada mountains, there could be another heavy snowstorm while towns at lower levels may see hazards as rains wash away recent snow. 

Breaking it down by time and region, here's what to expect over the next couple of days.

Radar map of atmospheric river 


NWS Meteorologist Brayden Murdock said rain will start around 4 a.m. Thursday, starting light and patchy but becoming widespread throughout the Bay Area later in the morning.

The North Bay and coastal areas will get hit the hardest during the morning hours, Murdock said.

After 10 a.m., the rain will pick up in intensity across the entire Bay Area and continue into Friday morning.

A flash flood watch for the entire Bay Area takes effect at 1 p.m. and is scheduled to be in effect until Sunday morning at 10 a.m. City streets could become inundated and there may be a sharp rise in the levels of streams and creeks. There are also concerns that the Russian River and Napa River may spill over their banks.

The evening commute could be a mess for workers returning home. 

Along with rainfall strong southerly winds will develop on Thursday with wind gusts up to around 50 mph, according to NWS. These winds may blow down trees resulting in power outages and blocked roadways. 

Evacuation warnings and orders have been issued for residents in parts of Santa Cruz and Monterey counties due to the likelihood of flooding.

"If you flooded in January, you are likely to flood again," Santa Cruz County warned in a tweet.

A winter storm warning takes effect Thursday at 4 p.m. in the Sierra Nevada mountains for areas at 7,000 feet or higher elevations. Two to three feet is snow could fall there while at lower elevations, rains may wash away the snow that had built up in recent weeks.

MORE: San Leandro neighbors fear atmospheric river after repeat canal collapses caused by storms


The heaviest rains will stretch into early Friday morning, but will lessen throughout the day.

Still, commuters in the South Bay and Santa Cruz mountains may deal with heavy rain during their commutes.

NWS meteorologist Roger Gass said the storm will focus more south, along the Big Sur coast.

"We are concerned about this storm and the potential for flooding," Gass said. "It's another 1-2 punch for the Bay Area."

Rivers, creeks, streams, and other low-lying areas could experience flooding, officials warned. Flooding of streets and poorly draining urban areas is also possible.

The San Lorenzo River is forecast to reach flood stage on Friday morning while the Alameda Creek is expected to flood on Friday afternoon. 

The Russian River near Guerneville is expected to be close to flood stage on Friday night, but it may crest without overflowing. 


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The already heavily saturated Bay Area was set to get more rain this week, prompting a flood watch warning for the region and a rush to get sandbags in place.


Gass said the region won't go dry and rain will turn into drizzle on Saturday, with yet another storm brewing into next week.

He said the entire area is at risk for shallow mudslides and rockfalls onto the roadways.

Colin McCarthy, a freshman studying atmospheric sciences at UC Davis, calls the next storms "a train of atmospheric rivers."

"You know it's going to be wet in California when the precipitation anomaly is literally off the charts over the Sierra Nevada," said McCarthy on his US_Stormwatch Twitter account, adding California could see rain measuring in feet over the next few weeks.

Sunday and later

The long-term forecast is less certain, but there is the likelihood of significantly more precipitation next week. Several inches of rain could fall in the Bay Area while there could be several feet of snow in the mountains near Lake Tahoe. Temperatures, however, should be warmer.