REDDING, Calif. — Heavy rain and flash flooding soaked roads in northern California, leading to water rescues from vehicles and homes and at least one confirmed death, authorities said Monday.

In Redding, a city at the northern end of the Central Valley, one motorist died after calling 911 while trapped in their vehicle as it filled up with water, Mayor Mike Littau posted online Monday. Police said they received numerous calls for drivers stranded in flooded areas.

“Redding police officer swam out into the water, broke the windows and pulled victim to shore. CPR was done but the person did not live,” Littau wrote.

The weather in the coming days could be even more dangerous, he warned.

The National Weather Service expected more rain through the Christmas week as a series of atmospheric rivers was forecast to make its way through Northern California. A large swath of the Sacramento Valley and surrounding areas were under a flood watch through Friday.

The weather pattern was expected to intensify by midweek, which could lead to potential mudslides, rockslides and flooding of creeks and streams, forecasters warned. Up to 6 feet of snow was predicted for parts of the Sierra Nevada and winds could reach 55 mph in high elevations by Wednesday.

Southern California can also expect a soggy Christmas, with heavy rain in the forecast starting Tuesday evening. The National Weather Service urged people to make backup plans for holiday travel.

In Redding and surrounding areas, between 3 and 6 inches had fallen by Sunday night, the National Weather Service said.

As of Monday morning, local roads in Redding remained flooded as street crews worked to clear debris and tow out abandoned cars.

Dekoda Cruz waded in knee-deep muddy water to check on a friend’s flooded tire business, where the office was littered with a jumble of furniture and bobbing tires.

In the mountain pass area of Donner Summit, firefighters in Truckee extended a ladder to stranded residents at a house along the South Yuba River, the fire department posted online Sunday. No injuries were reported.

Atmospheric rivers are long, narrow bands of water vapor that form over an ocean and flow through the sky, transporting moisture from the tropics to northern latitudes.

Earlier this month, stubborn atmospheric rivers that drenched Washington state with nearly 5 trillion gallons of rain in a week, threatening record flood levels, meteorologists said. That rainfall was supercharged by warm weather and air plus unusual weather conditions tracing back as far as a tropical cyclone in Indonesia.

Southern California is preparing for a powerful winter storm over the Christmas holiday, with forecasters warning of heavy rainfall, gusty winds, and potential flooding across the region.

According to the National Weather Service, the storm will bring an extended period of significant rainfall from Tuesday through Saturday, with totals expected to reach 4 to 8 inches across coastal and valley areas and 8 to 12 inches or more in the foothills and mountains by Saturday evening. Officials are urging residents to take necessary precautions, as flooding and debris flows could pose serious risks throughout the week.

The first, and most impactful, surge of rain is expected Tuesday night into Wednesday, when a moderate to strong atmospheric river will target the area. During this period, rainfall totals could reach 2 to 5 inches in coastal and valley regions and 5 to 10 inches in foothills and mountain areas, with hourly rates of 0.75 to 1.25 inches possible. The extended rainfall and intensity raise concerns about widespread urban flooding, mud and debris flows, and hazardous driving conditions, particularly during one of the busiest travel periods of the year.

A flood watch has been issued for all four counties from Tuesday afternoon through Wednesday evening, and the National Weather Service recommends that residents begin taking protective actions now.

In addition to heavy rain, strong southerly winds are expected Tuesday and Wednesday, particularly in the mountains and foothills, with the potential to knock down trees and cause power outages. Officials are advising residents to avoid swollen creeks and rivers, refrain from unnecessary ocean activity, and take precautions such as parking vehicles away from tall trees during periods of strong wind.

Forecasters emphasized that the timing and intensity of the storm could still change and encouraged residents to monitor updates from the National Weather Service and KTLA’s meteorologists.

A massive fog bank that has been blanketing much of California’s Central Valley with low-lying clouds since Thanksgiving time has prompted fears online of a mysterious and harmful “radiation fog,” but scientists say this is a misunderstanding of basic scientific terms and common weather patterns in the region.

“There’s something in the fog that I can’t explain,” a California man said in a recent video as he wiped soot from his truck bumper, in a post by Wall Street Apes, a popular X account.

There is indeed a “radiation fog” over the region, but that term refers to the general radiation of energy, not nuclear radiation. During radiation fog events, or “tule fog” as it’s known in California, named for a native marsh plant, fog forms when the moist ground cools rapidly at night, causing water vapor in the air to condense into thick fog.

A rainy autumn and winter in California, as well as a late November high-pressure system over the state, has further exacerbated this effect, helping create a fog bank that often stretched 400 miles up the center of the state.

Residents described the fog, which may actually be getting less common in the region compared to historical trends, as cold and eerie.

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“It’s like going into a dream stage where you can’t see anything around you,” David Mas Masumoto, a peach farmer in the San Joaquin Valley, told The New York Times. “You feel like you’re in this twilight zone.”

Masumoto added that he can’t remember another time with such thick fog in the last 50 years.

As for the particles that some residents were seeing in the fog, there’s a standard explanation for those too.

“Fog is highly susceptible to pollutants,” Peter Weiss-Penzias, a fog researcher at UC Santa Cruz, told The Los Angeles Times.

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The Central Valley, home to the state’s key north-south highway and miles of agricultural land, is known for its poor air quality.

“It could be a whole alphabet soup of different things,” Weiss-Penzias added.

The fog, which continued through late this week, is expected to thin out as heavy rains disrupt weather patterns in the state.