Californians are being warned of potentially life-threatening flooding over the weekend and into early next week as a second powerful atmospheric river storm makes landfall from the Pacific Ocean.
The state has already faced several inches of rainfall this week after a “plume of moisture” from the subtropics made its way eastward on Thursday and into Friday. Another, potentially stronger, atmospheric river storm is expected to bring heavy precipitation to southern California from Sunday.
“Concern is quickly growing for a very serious atmospheric river event in southern California Sunday through Tuesday,” Matthew Cappucci, an atmospheric scientist and meteorologist, wrote on Thursday.
Flash flood watches are in place for a swathe of the region. The National Weather Service (NWS) station in Los Angeles said “very high amounts” of rain would make “life-threatening and damage flooding” possible.
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“This storm could end up generating unprecedented amounts of rain across a widespread area,” it noted in a forecast. “This is potentially a very dangerous situation and everyone in this area needs to take precautions now.”
The NWS is predicting there was at least a 25 percent chance of the Ventura River reaching the flood stage by Monday morning, with “significant rises” in the Santa Ynez and Santa Clara rivers as well.
Residents have been told to change travel plans to avoid dangerous roads, protect flood-prone areas with sandbags and prepare for potential evacuations, particularly in areas near waterways.
Western states have already faced several bouts of snowfall so far this winter, having been subjected to a “prolific series” of atmospheric river storms from the Pacific.
Around the same time last year, California was battered by a parade of deadly storms that brought severe flooding. Thousands of homes were left without power and many people were evacuated.
While the impacts of the storm are expected to begin to be seen on Sunday, the NWS warned that the first wave of heavy precipitation could arrive as early as Saturday night.
In southern California, up to six inches of rain is anticipated for the coast and valleys and as much as a foot in the mountains—though some areas could see as much as 15 inches of rain. Mountain ranges in the region are also expected to see up to four feet of snow in places.
The NWS station in Los Angeles is forecasting over five inches of rain for Los Angeles, rising to more than six inches for Pasadena. Santa Clarita will see over five inches, while Big Pine Mountain could be subject to nearly 11 inches of rain from Saturday night through to Monday.
Atmospheric rivers are narrow channels in the atmosphere that are able to carry a large amount of moisture with them. They form when cold air from the Arctic meets warm, moist air from the tropics, cooling it to form heavy precipitation.
According to the National Oceanic and Atmospheric Administration, a strong river can transport as much as 15 times the amount of water flowing through the mouth of the Mississippi River.
California naturally has an atmospheric river flowing towards it that travels from the subtropics, known colloquially as the Pineapple Express.
Uncommon Knowledge
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Newsweek is committed to challenging conventional wisdom and finding connections in the search for common ground.