CNN
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More than 15 million people from California to Wisconsin are under winter weather alerts Sunday as the Pacific storm system that brought record-setting rainfall and severe flooding pushes east.

Some residents in Northern California are still grappling with epic flooding and power outages after the storm system led to highway closures and water rescues Saturday.

The city of Oakland had its wettest day on record Saturday, with 4.75 inches of rain in a 24-hour period – beating the previous record set on January 4, 1982, the National Weather Service office in San Francisco said.

The severe weather was caused by a powerful atmospheric river – a long, narrow region in the atmosphere that can carry moisture thousands of miles, like a fire hose in the sky.

Now, as that same storm system heads east, it could dump a foot of snow across the Sierras and up to 2 feet of snow in parts of the Rockies by late Monday. Local forecasters warn travel could be difficult.

The severe weather, which included high winds, left about 235,000 homes, businesses and other power customers without electricity in California and Nevada on Sunday, according to Poweroutage.US.

The storm also forced some Northern California residents out of their homes on New Year’s Eve as streets started to flood and evacuation orders and warnings were issued.

In addition to urban flooding, several rivers started overflowing – including the Cosumnes and Mokelumne rivers and the Mormon Slough, according to the National Weather Service in Sacramento.

Despite the flooding headaches, the moisture is actually a relief for drought-stricken California – which started 2022 with the driest beginning of the year on record and ended the year with drenched roadways and thick mountain snow.

But it’s not clear how much the storm will make a dent in California’s drought conditions.

Officials ordered residents in Wilton – roughly 20 miles from Sacramento – to leave the area immediately at one point Saturday, warning that rising water may spill onto roadways and cut off access to leave the area. About two hours later, Wilton residents were told to shelter in place after water made roads “impassable.”

Three communities near the city of Watsonville were also told to evacuate by the Santa Cruz County Sheriff’s Office due to creek flooding, while the rising San Lorenzo River waters prompted evacuations in the communities of Paradise Park and Felton.

In San Ramon, police used an armored rescue vehicle to evacuate residents from floodwater.

“Flooding impacts continue to escalate as this rain continues with too many road closures to count at this point,” the NWS said Saturday. The weather service told residents to stay put amid reports of rock and mudslides across the foothills and road closures across the Sierra passes.

Sacramento Metropolitan Fire District crews performed water rescues and responded to drivers whose vehicles became disabled after they drove through standing water Saturday, officials said.

Calling it “Stormageddon,” the Amador County Sheriff’s Office shared an image of cars up to their doorhandles in floodwater.

Highway 50 reopened just after midnight, hours after a section between Pollock Pines and Meyers was closed due to flooding from the American River. Another section was closed over Echo Summit for avalanche control work.

Interstate 80 was also partially closed near the Nevada line Saturday “due to multiple spinouts over Donner Summit,” the California Department of Transportation said.

By late Sunday morning, I-80 in the Sierra-Nevada Mountains had reopened to passenger vehicles only, “with R2 chain restrictions,” California Highway Patrol in Truckee tweeted. The restriction means chains or traction devices are required on all except four-wheel-drive vehicles with snow tires on all four wheels.

“The roads are extremely slick so let’s all work together and SLOW DOWN so we can keep I-80 open,” the agency said.

US Highway 101 – one of California’s most famous routes – was also temporarily closed in both directions in South San Francisco with the California Highway Patrol reporting “water is not receding due to non-stop rainfall & high tides preventing the water to displace.”

In the Sacramento County area, residents were advised to avoid travel as wind gusts of up to 55 mph toppled trees and covered roads with debris, according to a tweet from the National Weather Service in Sacramento.

The county proclaimed a state of emergency, saying the atmospheric river has caused “significant transportation impacts, rising creek and river levels and flooding” in the Wilton area.

Downtown San Francisco got 5.46 inches Saturday, making it the second wettest day on record for the area, according to the National Weather Service in the Bay Area.

This heavy rainfall is expected to slide southward to Southern California on Sunday, accompanied by gusty winds of 30 to 50 mph.

While parts of Northern California grapple with heavy rainfall, mountainous areas are getting covered with snow.

The UC Berkeley Central Sierra Snow Lab reported 7.5 inches of snowfall per hour between 4 and 5 p.m. Saturday in Soda Springs, about 30 miles from Lake Tahoe, and shared video of thick snow blanketing the area.

The lab said it had unofficial measurements of more than 30 inches of snow on Saturday.

Over a foot of new snow fell at Mammoth Mountain’s Main Lodge Saturday, the ski resort said on Facebook, adding that work will take place across the mountain since all lifts were coated in ice and “avalanche danger is extremely high.”