15 Million Under Flood Watch As Yet Another ‘Atmospheric River’ Approaches

Topline

More than 15 million residents in northern and central California have been placed under drought watches as yet another band of intense rain approaches the state, which has been alleviated of its harshest drought conditions following a series of storms this year, though forecasters warn the effects of more rain and melting snow could be severe.

Forecasters warn more flooding could hit California this week, as another storm approaches.

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Key Facts

Nearly all of California’s Central Valley, up through the Oregon border, were placed under a flood watch Monday morning, while the Sierra Nevada Mountains are under a winter storm warning, according to the National Weather Service.

The San Francisco Bay area, meanwhile, is under a high wind warning, as a long and narrow band of rain called an “atmospheric river” approaches the state, bringing a “moderate risk of excessive rainfall” through Wednesday.

Rainfall is expected to intensify Monday night and cause “considerable flooding impacts” in areas lower than 5,000 feet from the Sierra Nevada foothills to the coast, the NWS warns, adding the flooding is expected to have a significant effect on streams and large rivers.

The atmospheric river comes after not only a series of rainstorms that caused widespread flooding in both northern and southern California earlier this year, but snow storms in the Sierra Nevadas that have so far offloaded more than 50 feet of snow in some high-elevation areas.

Forecasters warn the combination of intense rain and melting snowpack in mountainous areas will exacerbate flooding conditions, which have already prompted California Gov. Gavin Newsom (D) to expand state-of-emergency declarations to six counties in northern and central California.

Surprising Fact

Nearly half of California has been lifted out of drought conditions earlier this month, nearly three months after the entire state had been in a state of drought. Other parts of California’s Central Valley and the Los Angeles area, which had been under “extreme” drought conditions, were downgraded to an “abnormally dry” classification, according to the U.S. Drought Monitor. In its updated map released last week, almost the entire Central Valley was lifted out of drought conditions, while “severe” drought conditions were limited to an inland stretch of northern California west of the Sierra Nevadas, as well as the Mojave Desert in southern California.

Contra

Despite the heavy precipitation starting with a New Year’s Eve storm, some scientists still warn the state is far from the end of its drought—if that period ever comes. Andrew Schwartz, a scientist with the University of California Berkeley’s Central Sierra Snow Lab told CNN earlier this month an expected and “prolonged dry and warm period” will likely leave California in an unfavorable spot later this month and into April. Water usage has become a growing concern among state officials, who in January refused to sign a proposal from six other southwestern states that rely on the Colorado River to restrict water usage. Officials are also considering a proposed $16 billion project to capture groundwater below the San Joaquin River Delta to central and southern California.

Key Background

California recorded its driest three-year period in October, breaking a previous record set between 2013 and 2015, the Los Angeles Times reported. Both droughts made up a larger “megadrought” that has been affecting the southwestern U.S. for decades. A study published last February in Nature Climate Change found the 20-year-period ending in 2021 was the driest in roughly 1,200 years. Researchers have also observed considerable drops in water levels in the region’s two largest reservoirs—Lake Mead and Lake Powell—sparking concerns the water bodies, which also produce power at high-power dams, could reach an irreversible level called “dead pool,” when those dams fail to produce power. In a surprising weather phenomenon over the past three months, however, California residents have faced widespread flooding, coastal erosion, mudslides, disrupted travel and power outages caused by what forecasters had dubbed a “relentless parade” of storms. The state’s Water Resources Control Board last week approved a plan to divert flood water from the San Joaquin River, east of San Francisco, to areas depleted by agricultural pumping, the Los Angeles Times reported, after residents and officials bemoaned the state’s inability to capture stormwater that drained into the Pacific Ocean.

Big Number

52. That’s how many feet of snow the Central Snow Lab has recorded since October 1 at its base near Lake Tahoe in the Sierra Nevadas, making it the fourth snowiest winter on record.