Big Storms Are Coming, But Feared Widespread Disaster Isn’t Looming

National Weather Service offices and other reputable meteorologists in California have been doing rumor control about the coming stormy period. Chatter on social media from unreliable sources had implied that the entire state will soon be underwater.

Daniel Swain, a meteorologist and climatologist at UCLA who knows a thing or two about California underwater, wants to assure the public that statewide inundation is not going to happen in the next few weeks.

Which is not to say that significant regional flooding, including in San Diego, is off the table in early February.

Swain has studied and written about the so-called “ARkStorm” scenario, where a virtual conveyor belt of atmospheric rivers (what the “AR” in ARkStorm stands for) repeatedly slams into the state over weeks, causing massive, widespread flooding that no one alive today has witnessed. 

That set-up caused the greatest flood in California history, in 1861-62. Total damages from the Oregon border to San Diego were estimated at $100 million, which in today’s dollars would top $3 billion.

Swain and other climatologists have concluded that a repeat of that disaster is inevitable, and probably within the next 50 years. In today’s much bigger and more highly developed and populated state, damages would likely be in the trillions of dollars. 

But that atmospheric arrangement is clearly not going to evolve in the next 15 days, he said.

“Most of us will live to see an event like this in our lifetime, but the odds of it happening in the next two weeks are practically zero,” Swain said. “An ARkStorm is not on the horizon.”

But Swain said the position of a very strong Pacific jet stream is likely to put Southern California in a very favorable spot for heavy downpours starting the second half of this week. 

“The real interesting thing is what happens next,” Swain says. “This really ramps up a lot in Southern California.”

Three to six inches of rain is possible along the coast in less than 10 days, he said. Strong winds, thunderstorms, snow in the mountains and even water spouts at the coast could also be in the mix.

Forecast models have been converging and consistent, he said, and a swing back to a drier, less-severe forecast looks unlikely.

The National Weather Service now expects a strong cold front to arrive in Southern California Thursday. Rain associated with an atmospheric river should become heavy in the afternoon. Showers are expected on Friday. Rainfall totals should range from 1 to 2.5 inches west of the mountains by late Friday. 

A second storm, also fed by an atmospheric river, is now expected to bring another intense round of precipitation Monday and Tuesday.  “Significant” rainfall along the order of the first storm is likely, says the weather service.

And, they say cool, wet, and windy weather will likely continue through the first full week of February. 

If that stormy pattern does continue as expected, combined with the record-breaking downpours of Jan. 22 that caused significant flooding and damage, San Diego could record 75 percent of its annual average rainfall (9.79 inches) in less than three weeks. 

Update: This story has been undated to include predictions for Friday.