California, struggling with weekend floods, braces for new atmospheric river

A new atmospheric river is expected to wash ashore this evening over California, where neighborhoods are still under water from a weekend of devastating floods and emergency rescues.

“The incoming atmospheric river will bring more heavy rain and flooding concerns beginning tonight,” the Bay Area branch of the National Weather Service (NWS) warned Monday morning.

Advising drivers to prepare for potential road closures and to refrain from navigating flooded roadways, the NWS offered an ominous instruction: “Turn around, don’t drown!”

The “moderate to strong atmospheric river” will likely cause “significant impacts” through Tuesday night, including potentially damaging winds, power outages and flooding, according to an NWS Bay Area outlook.

The meteorologists predicted “difficult to impossible travel for some areas,” as well as a “direct threat to life and property from water and wind impacts.”

“This one is taking shape now over the Pacific Ocean between the Hawaiian Islands and California,” University of California, Los Angeles climate scientist Daniel Swain said during virtual “office hours” on Monday.

“This is yet another warm ‘Pineapple Express’ type atmospheric river,” he added, referring to the nickname for last week’s storm system.

A statewide outlook from the NWS’s Weather Prediction Center forecast an intensification of rain and snow through Wednesday, leading to “considerable flooding impacts below 5,000 feet” — across the coastline, the Central Valley and the southern Sierra Nevada foothills.

The new storm will arrive before many residents have had a chance to recover from the previous atmospheric river, which forced thousands of Californians to evacuate this weekend and left at least two people dead.

“It’s been a pretty, pretty crazy period in California weather,” Swain said during the virtual office hours.

More than 8,500 people were under evacuation orders in Monterey County this weekend, after the Pajaro River’s levee was breached by heavy rainfall.

Swain described the town of Pajaro as “essentially inundated,” noting that the situation could become “worse again with the incoming storm.”

As of Sunday, the Monterey County Sheriff’s Office reported more than 90 completed rescues, conducted with the help of the California National Guard.

The same day, Gov. Gavin Newsom (D) extended a state of emergency to support storm response and relief initiatives in six new counties, in addition to the original 34 counties he had cited last week.

This latest proclamation follows an emergency declaration last week from President Biden — at Newsom’s request — authorizing federal assistance to support local recovery efforts.

By Monday morning, 11,773 Californians still had no electricity, according to the grid tracker PowerOutage.us. Some 1,627 of those outages concentrated in Monterey County and 2,080 in the adjacent Fresno County, per the site.

With a new atmospheric river on the horizon, California’s Office of Emergency Services warned on Monday that “additional flooding on rivers and streams is likely” through later this week.

The agency also forecasted possible flash floods, noting that the most vulnerable areas are those along the western slopes of the Sierra Nevada and along the Central Coast.

“There are two reasons why I think this moderate to strong atmospheric river is going to cause bigger problems than the perhaps similar moderate to strong atmospheric river we saw late last week,” Swain said during his office hours.

The first issue, he explained, is that the soil is already extremely wet and in some cases even “super saturated.”

“It’s not going to take a whole lot of precipitation to result in immediate runoff and rises on rivers and streams,” Swain said.

The second problem is that a low-pressure system off the coast of Northern California may come not only with heavy rainfall, but also with significant winds, according to Swain.

While the climate scientist had some words of caution about the incoming storm, he expressed much greater alarm over what could happen in the weeks ahead.

“Right now, there is more snow water in the southern and possibly central Sierra than there has ever been at this time of year — and possibly at any point during the year,” Swain said.

“There is a whole hell of a lot of water up there right now stored in snowpack,” he added.

And while that snow is not likely to melt during this week’s atmospheric river, Swain warned that flooding will become “a growing concern for later this season.”