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President Joe Biden has declared a state of emergency in California due to successive winter storms that have caused extensive damage, flooding and claimed at least 12 lives, according to a statement from the White House.

Biden ordered Federal assistance to help state, tribal and local response efforts to deal with the conditions brought on by the storms in the counties of El Dorado, Los Angeles, Mariposa, Mendocino, Merced, Monterey, Napa, Placer, Riverside, Sacramento, San Bernardino, San Mateo, Santa Clara, Santa Cruz, Sonoma, Stanislaus and Ventura.

The National Weather Service warned of a “relentless parade of atmospheric rivers” — storms that are long plumes of moisture stretching out into the Pacific and are capable of dropping staggering amounts of rain and snow. Two major storms are expected to drop heavy rainfall on the coast and snow in the mountains over the next couple of days.

For days, California has been walloped by Pacific storms that last week knocked out power to thousands, flooded streets, and battered the coastline with high surf.

The first of the newest, heavier storms prompted the weather service to issue a flood watch for a large swath of Northern and Central California, with 6 to 12 inches (15 to 30 centimeters) of rain expected through Wednesday in the already saturated Sacramento-area foothills.

In the Los Angeles area, stormy conditions were expected to return Monday, with the potential for up to 8 inches (20 centimeters) in foothill areas. High surf was expected through Tuesday, with large waves on west-facing beaches.

Gov. Gavin Newsom said 12 people died as a result of violent weather during the past 10 days, and he warned that this week’s storms could be even more dangerous. He urged people to stay home and asked President Joe Biden to declare a federal emergency to support storm response and recovery efforts.

Since Dec. 26, San Francisco received more than 10 inches (25 centimeters) of rain, while Mammoth Mountain, a popular ski area in the Eastern Sierra, got nearly 10 feet (3 meters) of snow, the National Weather Service reported.

The storms won’t be enough to officially end California’s ongoing drought — but they have helped.

State Climatologist Michael Anderson said at a news briefing late Saturday that officials were closely monitoring Monday’s incoming storm and another behind it and were keeping an eye on three other systems farther out in the Pacific.