California is bracing for a stronger atmospheric river this weekend

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A stronger, longer-lasting atmospheric river event is set to hit California this weekend, presenting a high risk of flash flooding, mudslides, damaging winds and heavy mountain snow. Nearly 40 million people are under a flood watch including San Francisco, Sacramento, Los Angeles and San Diego.

“The odds are increasing that a prolonged period of heavy rain will develop late Saturday night and continue through most of Sunday and Monday,” the Los Angeles office of the National Weather Service (NWS) warned. “This storm could end up generating unprecedented amounts of rain across a wide area!”

Rain is expected to begin early Saturday night in central parts of coastal California where a few inches of rain by early Sunday morning could lead to flooding. Repeated rounds of storms could bring the risk of rainfall of more than 5 inches, especially along the Santa Cruz Mountains and Big Sur Coast.

In Southern California, rainfall totals are expected to range widely from 3 to 6 inches — the equivalent of more than a month’s rain for most people. Los Angeles averages 2.99 inches of rainfall in February – the wettest month of the year on average. In the mountains and foothills of Southern California, the NWS expects up to a foot of rain.

This new atmospheric river comes on the heels of a storm that brought record rainfall to much of California including Sacramento, Eureka and Los Angeles, but these upcoming storms are not the same.

The incoming storm is much slower and is expected to stop as it moves onshore, resulting in much longer rainfall compared to the first storm.

The weather service fears the possibility of nearly continuous moderate to heavy rain for up to 48 hours on Sunday and Monday.

Fears of flooding and mudslides are increasing because the ground is already wet from the first storm.

Los Angeles International Airport picked up nearly a month’s worth of rain — 2.49 inches — Thursday.

The ground is also saturated in the far north from the heavy rains at the beginning of the year. Crescent City and Eureka had their wettest January on record and are now expecting 1 to 3 inches of rain through Tuesday.

CNN Weather

The Weather Prediction Center issued a level 3 out of 4 risk of heavy rainfall for Santa Barbara and Oxnard on Sunday. Level 2 is more prevalent across much of coastal California including San Francisco all the way to Los Angeles.

On Monday, Level 3 of 4 extends south to include Los Angeles.

High winds will also be a concern across much of California with widespread sustained winds of 40-60 mph with gusts as high as 75-80 mph. This will likely lead to fallen trees and power outages.

“Confidence is strong that this will be as much a wind event as it will be a rain event,” the NWS office in San Francisco said. “If anything recent model guidance has doubled the wind potential.”

Wind warnings and high wind warnings extend across almost the entire state of California from Redding to San Diego, affecting nearly 30 million people.

For coastal central California, there is also the potential for severe storms on Sunday including in San Jose and Salinas. The main threats are isolated tornadoes and damaging winds.

This storm is not just rain and wind, it will also bring significant snowfall.

“What appears to be the most significant and impactful storm of the winter so far is knocking on our door,” said the NWS office in Reno, Nevada, which also forecasts parts of California. “Plan for major travel impacts in the Sierra Sunday through Tuesday due to heavy snowfall. Better get where you want to be on Saturday and hunker down until this storm is over.

And in eastern California, along the Nevada border, Mono County, home to popular tourist destinations like Mammoth Lakes and Yosemite National Park, is the target of what could be significant snow totals.

“Mono County will take a double hit from this storm, with snowfall totals significantly higher as a result,” the NWS office in Reno said. “Through Monday night, there is an 80-90% chance of 4+ feet of snow above 8,000 feet (yes, that includes Mammoth Lakes).”

CNN Meteorologist Taylor Ward contributed to this story.

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