‘Not done yet’: California flood risk is already high. More atmospheric rivers may come

A stretch of intense wet weather will continue this week in California, once again creating flood risk as another atmospheric river brings more rain across the Sacramento and San Joaquin valleys, the Sierra Nevada foothills and central portions of the coast.

And after that, even more atmospheric rivers could arrive before the end of next week, state water officials said Monday.

The first of the incoming storms is forecast to last from Monday night through Wednesday, and will likely peak in intensity Tuesday, according to the National Weather Service.

The Sacramento region and foothills east of the capital region were spared from major flooding last week, as the most recent atmospheric river storm veered south.

But virtually all of interior Northern California is again under a flood watch by the weather service due to this week’s incoming atmospheric river. Parts of the Sacramento Valley could receive up to 3 inches of rain from Monday night through Tuesday night, with as much as 7 inches possible in parts of the foothills.

Flood concerns remain highest in the foothills and along the central coast, according to the weather service. In the foothills, rain could melt off snow that fell during prior storms from late February through early March.

Thirteen points along rivers and creeks are expected to exceed their flood stages this week, and 32 others are expected to exceed monitoring stages, said Jeremy Arrich, manager of the Department of Water Resources’ division of flood management, during a virtual news briefing Monday by the California Department of Water Resources.

Most of those locations are in the Sacramento and San Joaquin valleys, including the Sacramento, Cosumnes, Tuolumne and Merced rivers. A handful are in coastal areas, including the Salinas River.

Flooding, a levee break and a tornado

A strong atmospheric river storm late last week created heavy flooding in central parts of California, along the coast and in the Valley, accompanied by weekend thunderstorms and a Saturday tornado that touched down in rural Tuolumne County with winds at 90 mph.

Closer to the coast, authorities evacuated the Monterey County town of Pajaro and surrounding areas Saturday morning in response to a then-imminent levee failure.

State and local flood crews working on the levee “determined it was no longer safe to continue operations, so they cleared the area,” Arrich said.

“The levee there in Pajaro River failed shortly after emergency crews cleared the site,” Arrich said. State water officials have exercised authority to fund emergency work on the break in the levee, which is county-operated, he said.

Mandatory evacuations were also ordered Friday in the Modesto area due to floodwaters. Emergency officials in Stanislaus County issued evacuation orders and warnings beginning Friday along stretches of the Tuolumne River in Modesto and the San Joaquin River near Patterson, Newman and Grayson.

Forecasts show this week’s atmospheric river storm should be very similar in magnitude to Friday’s system in the San Joaquin Valley, state climatologist Michael Anderson said in Monday’s briefing.

Supervisors in Stanislaus County on Tuesday are expected to ratify an emergency proclamation due to storms and flooding, the county’s second such declaration since January.

Sacramento, El Dorado and Placer counties issued local emergency proclamations earlier this month.

40 California counties now under state emergency proclamation

Forty of California’s 58 counties are now under an emergency proclamation by Gov. Gavin Newsom, who on Sunday expanded the order to include Calaveras, Del Norte, Glenn, Kings, San Benito and San Joaquin counties.

President Joe Biden last week issued a presidential emergency declaration, authorizing federal aid for state and local storm response, following a request from the Newsom administration.

Arrich said state water officials have contributed with flood assistance in recent weeks to Merced, Monterey, Sacramento, Kings, Tuolumne, Mariposa, San Luis Obispo, Fresno, Inyo, San Joaquin and Madera counties.

More storms are on the horizon for California

“We’re not done yet,” Anderson said in Monday’s briefing.

One to two more atmospheric rivers could strike the state between March 19 and March 22, Anderson said, though the exact timing and magnitude of those storms are “highly uncertain” at this time.

Anderson also predicted that California is very likely to break snowpack records this winter. Snow has pounded the mountains since late February, with heavy snow also falling in the foothills from late February through early March.

City and fire officials in South Lake Tahoe reported numerous roof cave-ins from Thursday through the weekend due to heavy snow, including at a Raley’s supermarket.

State water officials said following a monthly snow survey in early March that this winter’s storms had the state “hovering just below” the all-time record set in 1982-83.

State water data as of Monday showed California at 215% of its average snowpack for the date, including 223% of normal in the central Sierra and 257% of normal in the southern Sierra.

The state and those two regions are also more than double their averages for April 1, which is the typical peak for California snowpack.

“By the time this is all done, we will either reach or exceed” regional snowpack records set in the central and southern Sierra in 1969, Anderson said. “It’s a good bet.”

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