Schools closed, evacuations issued as Southern California braces for storm: Updates

An atmospheric river was set to begin pummeling Southern California with heavy rain on Thursday, prompting evacuations and school closures as officials warned about life-threatening flooding and mudslides in areas charred by the wildfires that broke out across the region last month.

The evacuation warnings and orders were active in Los Angeles, Ventura and Orange counties, as well as in several communities along the foothills of the San Gabriel Mountains in San Bernardino County. In Santa Barbara, people living in at-risk areas were told to leave by 3 p.m. Wednesday.

Torrential downpours were not the only weather threat. Up to 6 feet of snow is expected to blanket California's mountains, while high winds have begun to knock out power and pile up disruptions at airports.

Authorities closed roads at risk of experiencing mudslides, including a large section of Pacific Coast Highway and Topanga Canyon Boulevard. In Malibu, the public school district shuttered all classrooms on Thursday "due to road closures and weather concerns."

Residents were urged to monitor emergency updates, prepare to evacuate by collecting important documents and medicine, and promptly flee their home if they are told to do so.

"When you're given an evacuation order, heed the order and leave as soon as you can. Nothing that you have back home is worth your life," said Los Angeles County Sheriff Robert Luna at a news conference Wednesday. "If you decide to stay in your property in an evacuated area, debris from the burn scar areas and storm may impede roads and we may not be able to reach you."

Los Angeles braces as worst storm conditions loom

Los Angeles Mayor Karen Bass told residents to stay off the roads as the worst of the storm's rain is expected Thursday afternoon through Friday morning.

"The heaviest rains are expected in a few hours," Bass said at a news conference Thursday morning. "There are risks all across Los Angeles, from mudflows in our hills to flooded streets, downed trees and fallen power lines."

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Bass, as well as state officials, announced a slew of measures to mitigate damage in the burn areas, including the installation of thousands of feet of concrete barriers to halt the progress of any possible mudflows. Hundreds of personnel have been prepositioned to assist in the disaster response.

Forecasters warn of ‘life threatening’ surf conditions

The storm is bringing dangerous surf conditions to the California coast, according to the National Weather Service.

A coastal hazard warning said dangerously large waves of 20 to 40 feet tall are breaking along the state’s beaches Thursday. Such waves “can sweep people off jetties and docks, and into dangerous seas,” the weather service in San Francisco said, adding that sudden immersion in cold water can also increase "the risk of drowning in rough open waters."

"Life-threatening swimming conditions and significant beach erosion can be expected," the weather service said.

Authorities give door-to-door evacuation notices ahead of storm

Leading up to the storm, officials went door-to-door notifying people their home was at elevated risk of mudflow and dangerous flooding.

Those residences were identified by the California Department of Public Works. Department director Mark Pestrella said Wednesday the vulnerable areas are not limited to neighborhoods such as Altadena and Pacific Palisades, which were ravaged by wildfires last month, but include any area where wildfires occurred within the last year.

Pestrella said authorities believe they have contacted every vulnerable resident, but urged those who are concerned about their residence to contact the department. He says vulnerable structures are those located below a slope that has been burned and where there is no drainage device in place to capture debris.

San Francisco airport sees ground delays amid high winds

Departing flights at San Francisco International Airport were delayed by an average of nearby two hours Thursday morning "due to high winds," according to the Federal Aviation Administration.

High wind warnings were in place along the coast of California from San Francisco to San Diego, according to the weather service. In San Diego, forecasters warned of 25 to 35 mph winds with possible gusts up to 60 mph.

"Damaging winds could down trees, snap power lines, and result in property damage," the weather service office in San Francisco said. "Widespread power outages are possible. Travel could be extremely difficult and hazardous, especially for high profile vehicles. The combination of wind and moist soils will increase the risk for downed trees."

School closures abound amid snow, frigid temperatures in the Northwest

Hundreds of schools across Oregon, Nevada, Idaho and Northern California canceled classes on Thursday as the region faced heavy snowfall from the atmospheric river.

Out of all the western states, the closures impacted Oregon the most, shuttering all Portland Public Schools, which serves over 44,000 students. In Portland, up to two inches of snow and sleet were expected as forecasters projected winds as high as 40 mph. Weather officials warned people to stay off icy roads.

"Roads, and especially bridges and overpasses, will likely become slick and hazardous," the weather service in Portland said. "Significant ice accumulation on power lines and tree limbs may cause power outages."

How much rain has fallen so far in California?

Below are preliminary two-day rainfall amounts reported by the National Weather Service as of Thursday 7 a.m. local time.

• Rocky Butte, San Luis Obispo County – 5.24 inches

• Las Tablas, San Luis Obispo County – 2.02 inches

• San Marcos Pass, Santa Barbara County – 1.69 inches

• Porter Ranch, San Fernando Valley – 1.42 inches

• Matilija Dam, Ventura County – 1.20 inches

6 feet of snow forecast for Sierra Nevada mountains

In the Sierra Nevada mountains, some areas could see up to 6 feet of snow, leading authorities to urge people to stay off mountain passes. Powerful wind gusts of 60 mph also posed a threat at high elevations.

"Travel could be very difficult to impossible," the weather service office in Hanford said. "The hazardous conditions could impact the Thursday morning and evening commutes. Very strong winds could cause extensive tree damage."

"If you must travel, keep an extra flashlight, food, and water in your vehicle in case of an emergency," the weather service added.

Wintry weather prompts state of emergency in Oregon

The blanketing snow will not be limited to the California mountains. Winter storm warnings were active in Oregon, Idaho, Nevada, Utah, Colorado, Arizona and New Mexico, according to the weather service.

In Oregon's Multnomah County, part of the Portland metropolitan area, officials extended a state of emergency through at least Thursday evening. The county opened six emergency shelters on Wednesday night after hundreds of people came to the open shelters a day earlier.

The National Weather Service in Portland warned freezing rain and snow will impact parts of Oregon and Washington state overnight into Friday. These conditions were also expected to impact major roadways, including Interstate 5, Interstate 205, and Interstate 84, according to the weather service.

What are atmospheric rivers?

Often referred to as "rivers in the sky," atmospheric rivers are long, narrow tracts of the Earth’s atmosphere that gather moisture from the tropics near the equator and sweep it toward the poles.

They can vary greatly in size and strength, however, the average atmospheric river carries an amount of water vapor "roughly equivalent to the average flow of water at the mouth of the Mississippi River," according to the National Oceanic and Atmospheric Administration.

Exceptionally strong atmospheric rivers can move up to 15 times that amount, often leading to "extreme rainfall and floods," NOAA said.