LA: In three weeks of severe winter storms, a ninth atmospheric river was churning through California on Monday, making mountain driving dangerous and increasing the risk of flooding near swollen rivers, as the sun began to shine in some places .

The National Weather Service has issued a travel advisory following heavy snowfall in the Sierra Nevada. After repeated weekend closures due to whiteout conditions, Interstate 80, a vital route connecting the San Francisco Bay Area to Lake Tahoe ski resorts, reopened with chain requirements.

"If you must travel, be prepared for hazardous travel conditions, significant travel delays and road closures," the weather service office in Sacramento posted on Twitter.

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The Central Sierra Snow Lab at the University of California, Berkeley tweeted Monday morning that it had measured 49.6 inches (126 cm) of new snow since Friday. The Greater Tahoe area was included in the Central Sierra's Backcountry Avalanche Warning.

Since late December, a barrage of atmospheric river storms has pelted California with rain and snow, leaving thousands without power, flooding roads, uprooting trees, blowing debris , and landslides are happening.

Despite Monday's storm system being relatively weak compared to earlier storms, forecasters warned that because the state was so saturated, there was still a risk of flooding and landslides. Dry days were expected for most of the week, although some areas of Northern California could see more rain through the middle of the week.

The weather cleared up Monday in San Francisco, where the airport has recorded 20.3 inches (51.5 cm) of rain since October 1, when California typically begins tracking annual rainfall. The San Francisco Weather Service office tweeted, "The water year" averaged 19.6 inches (49.8 cm), so "with eight more months to go, we've passed the annual total."

Ten homes in Berkeley were evacuated on Monday after a soggy hillside gave way, dumping mud into nearby homes. There were no reported injuries.

In the wet Sacramento Valley, where residents of Wilton and surrounding communities were warned to prepare to leave if the Cosmanes River rises further, up to 2 more inches (5 cm) of rain fell on Sunday .

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Over the weekend, the Salinas River in Monterey County was inundated, and officials reported Monday that it was still rising. On Saturday, Governor Gavin Newsom traveled to Merced County in the agricultural Central Valley, where flood warnings were still in place.

On Monday, Newsom signed an executive order to strengthen the state's emergency hurricane response and aid damaged communities. The state was deemed a major disaster by President Joe Biden, who also ordered federal aid to support local recovery efforts.

Although it was sunny in Los Angeles, Southern California, winter storm warnings and advisories were still in effect for the mountains, where many roads were impassable due to mudslides and landslides.

After a hillside collapsed, two northbound lanes of Interstate 5 near Caustic in northern LA County were permanently closed. The weather service reported that 1.82 inches (4.6 cm) of rain fell in Downtown Los Angeles on Saturday.

At least 20 people have died as a result of the storm, and a 5-year-old boy is still missing after being swept away by his mother's car in floodwaters in San Luis Obispo County.

Forecasters were keeping a close eye on it to determine whether the storm developing in the Pacific would strengthen enough to become the state's 10th atmospheric river of the season.

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When it makes landfall on Wednesday, it will most likely bring only light rain and be mostly confined to northern California, according to state climatologist Dr. Mike Anderson.