California braces for a strong atmospheric river this weekend

(CNN) — A strong and long-lasting atmospheric river event will affect California this weekend, bringing a significant risk of flash flooding, mudslides, damaging winds and heavy snowfall in the mountains. About 40 million people are under flood warnings, including San Francisco, Sacramento, Los Angeles and San Diego.

The Los Angeles office of the National Weather Service (NWS) warned, “An extended period of heavy rain will develop Saturday night and continue through most of Sunday and Monday.” “This storm could produce unprecedented rainfall over a large area!” he added.

Rain is expected to begin Saturday night along central parts of the California coast, where a few millimeters of rain could cause flooding early Sunday morning. Repeated rounds of storms could bring more than 120 mm of rain, especially along the Santa Cruz Mountains and along the Big Sur coast.

In Southern California, widespread rainfall of 75 to 150 mm is expected, equivalent to more than a month of rain. The wettest month of the year, February averages just over 75 mm of rain in Los Angeles. In the mountains and foothills of southern California, the NWS predicts up to 300 millimeters 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 this Saturday’s storm is different.

The storm front is much slower and is expected to stall as it moves toward the coast, resulting in a much longer duration of rain compared to the first.

The weather service is concerned about the possibility of near-continuous, moderate to heavy rain for 48 hours between Sunday and Monday.

Concerns about flooding and landslides are heightened because the ground is already wet from the first storm.

Los Angeles International Airport recorded almost a month’s worth of rain (63.25 mm) on Thursday.

Further north, the soil is also saturated due to heavy rainfall earlier in the year. Crescent City and Eureka had their wettest January on record and now expect between 25 and 75 mm by Tuesday.

The Weather Prediction Center issued a 3 out of 4 risk of excessive rain for Santa Barbara and Oxnard on Sunday. A more extensive Tier 2 exists along much of California’s coast, including San Francisco and Los Angeles.

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

Stronger winds will also be a concern, with winds gusting 64 to 96 km/h and some gusts of 120 to 128 km/h across much of California. Due to which trees are likely to fall and power supply may be disrupted.

“There is high confidence that this will be both a wind and rain event,” the NWS office in San Francisco said. “If anything, recent model guidance has doubled the wind potential.”

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

Severe thunderstorms are also possible along the Central California coast, including San Jose and Salinas on Sunday. The main hazards are isolated tornadoes and damaging winds.

This storm will not only bring rain and wind, but also significant snowfall.

“One of the most significant and impactful storms of the winter season so far is knocking on our door,” said the NWS office in Reno, Nevada, which also forecast for parts of California. “Plan for the possibility of significant travel impacts in the Sierra Sunday through Tuesday due to heavy snow. It is best to get where you need to be on Saturday and take shelter until this storm passes.”

In eastern California, along the Nevada border, Mono County, which includes popular tourist destinations such as Mammoth Lakes and Yosemite National Park, could see significant amounts of snow.

“Mono County will suffer a double whammy from this storm, resulting in significantly more snowfall,” the NWS office in Reno said. “By Monday night, there is an 80-90% chance of more than 120 centimeters of snow at 8,000 feet (yes, that includes Mammoth Lakes).”

CNN meteorologist Taylor Ward contributed to this story.