Water........

Atmospheric river poised to soak California next week. Here's what to know.

By Amy Graff

A series of atmospheric rivers is expected to bring heavy precipitation, powerful winds and potentially flooding to the West Coast late January into early February, and meteorologists in California are closely watching the forecast to determine what the impacts will be on the Golden State. 

The National Weather Service’s Climate Prediction Center has said there’s “greater than 60% chance” of hazardous and heavy precipitation across California at some point between Jan. 31 and Feb. 5.

Meteorologists are saying it’s too early to discuss the details, but are beginning to get out the word that California could get soaked by a series of storms. 

Brian Garcia, a meteorologist with the weather service’s Bay Area office, said computerized models that predict weather several days in advance are struggling to lock in specifics.

“We can see the moisture out across the western part of the Pacific, somewhere between Japan and Hawaii, and we know it’s heading to North America,” Garcia said. “The issue with trying to nail down specifics this far out is the storm still needs to transit nearly the entirety of the Pacific, where observations are extremely limited. So models can struggle to accurately forecast the precise direction. At this point, we are telling people to prepare for the worst and hope for the best simply because we don’t know where the biggest impacts will be at this time.”

Garcia said the shift in weather will be marked by an initial atmospheric river storm, likely arriving Wednesday into Thursday, with California staying in an active pattern in the days that follow.

Garcia said it’s accurate to call this storm an atmospheric river, or a pineapple express, as its moisture source is expected to stretch across the Pacific Ocean to the subtropics near Hawaii. Atmospheric rivers are named for the rivers of moisture that they carry across the ocean and dump as rain when they arrive on land.  

In the San Francisco Bay Area, Garcia said the system is most likely to bring about twice as much rain as the system that brought several rounds of rain last weekend. In that system, San Francisco saw 1.75 inches of rain across four days. He said there’s only about a 10% chance for a worst-case scenario where the Bay Area would be hit by a storm similar to one of the severe storms that dumped rain last winter.

The Los Angeles weather service is predicting that most locations along the coast between San Luis Obispo and LA counties could see 1 to 2 inches from Jan. 31 to Feb. 1. Higher elevations could pick up 2 to 4 inches. 

UCLA climate scientist Daniel Swain talked about the expected upcoming spell in a YouTube livestream on Friday. “It’s looking pretty darn interesting,” said Swain of the weather models. 

Swain said the initial atmospheric river that brings rain across the state will be followed by a sequence of storms that are likely to favor Central and Southern California. “We have a solid 10 days for major storm activity in Central and Southern California,” he said. 

The potential for flood risk is high in coastal Southern California, stretching from San Luis Obispo County southward, Swain said. 

“I don’t think this is a particularly concerning pattern for flood risk in the northern half or even in the northern two-thirds of the state,” he said. “The amount of precipitation in the next couple along the North Coast probably isn’t going to be all that extraordinary.”

Swain said the expected weather pattern could also bring a high risk for powerful, damaging winds and robust thunderstorm activity.

The weather service’s Los Angeles office alerted Southern California residents of the upcoming pattern change on Friday. It said the forecast storm looks “healthy but not extreme” with “a low risk for significant flooding” and most likely impacts to “be moderate and confined to the roads.”

Ahead of the rains, California is expected to see a mostly dry, mild period through the weekend and into early next week. The exception is far Northern California, which could see some rain this weekend, according to the weather service.