Atmospheric River Impacting California

January 4, 2023
A photo of the storm before it impacted the West Coast of the United States on Wednesday. Photo Credit: National Weather Service Bay Area official Twitter account

Heavy rain, damaging winds, and heavy mountain snow to impact California as an atmospheric river moves onshore tonight.

The National Weather Service Weather Prediction Center as a major “hurricane force” storm was set to hit California on Wednesday, bringing concerns of power outages, flooding and mudslides.

Why It Matters: This storm comes after California has already faced deadly flooding, leaving the soil soaked "like a wet sponge" and the region more likely to experience flooding and potential mudslides with further precipitation. Counties across the state have activated emergency operations, as evacuations and school closures have been ordered in areas likely to be most impacted. CA Governor Gavin Newsom has announced a statewide emergency declaration to "support response and recovery efforts" to the storm.

What's an "atmospheric river?" The National Oceanic and Atmospheric Administration describes them as "relatively long, narrow regions in the atmosphere – live rivers in the sky – that transport most of the water vapor outside of the tropics," explaining that these columns carry "an amount of water vapor roughly equivalent to the average flow of water at the mouth of the Mississippi River." When atmospheric rivers reach land, they release water vapor in the form of snow or rain. The atmospheric river impacting CA is described as a "Pineapple Express" because it's a strong system bringing "moisture from the tropics near Hawaii" to the state.

Big Picture: The atmospheric river isn't the only bad weather impacting the U.S. this week; "Heavy rainfall, flash flooding, and severe weather" is impacting the Southeast, the National Weather Service tweeted Wednesday morning. CNN reports that "More than 30 million people are under some sort of severe weather threat in the South," with potential tornadoes, hail, and flash flooding expected due to the "multi-hazard storm."

California Braces for Yet More Rain (The New York Times)

Southern California storm to unleash pounding rain for days due to atmospheric river (Los Angeles Times)

Damaging weather menaces the Southeast as a 'brutal' storm system threatens California with fresh flooding (CNN)

Photos: The California National Guard helps to "install flood dams and sandbags as #NorCal prepares for more storms midweek."

NOAA NWS Weather Prediction Center on Facebook: Key Messages for Early January Atmospheric Rivers

Governor Newsom Proclaims State of Emergency and Mobilizes State Government Ahead of Winter Storms (Office of Governor Gavin Newsom)

by Jenna Lee,

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