California atmospheric river: When and where are rain, snow coming?

A major atmospheric river storm bringing heavy rains, high winds and significant snow barreled into northwestern California early Wednesday and is expected to move south across the state over the next 48 hours.

Statewide, officials are bracing for potential widespread flooding, dangerous travel in the mountains and even power outages.

The system is the first of back-to-back storms that forecasters say could cause perilous conditions through next week, depending on the severity, strength and speed of the storm systems.

This first storm is expected to be relatively fast-moving, dumping excessive rain and heavy snow primarily on Wednesday and Thursday before moving out of the area, a scenario officials hope will help minimize damage.

Here’s the latest on when Californians can expect to see the storm’s impact:

Wednesday morning

After a dangerously windy night for much of the state’s northwest corner — and a high wind warning advisory remaining through 1 p.m. for much of the North Coast — showers began in Northern California early Wednesday.

Rainfall is expected to pick up throughout the day across the North Coast, the San Francisco Bay Area and the Sacramento Valley, with much of the region under a flood watch through late Thursday or early Friday.

But dangerous winds remain a major concern, with the National Weather Service issuing a high-wind warning for much of the North Bay and Central Coast through Thursday afternoon.

“Given saturated soils, downed trees and resulting power outages are likely,” the National Weather Service’s Bay Area office warned on X.

In the northern Sierra Nevada and other high peaks above 6,000 feet, heavy snowfall is expected to begin Wednesday morning, with a winter storm warning in effect through at least Friday. As the storm develops, snow levels are expected to drop through the rest of the week and snowfall rates could reach up to 2 inches an hour, according to the weather service. Up to 3 feet of powder is possible at the highest peaks.

Wednesday afternoon

As the storm moves south and east, much of the Sacramento Valley will enter a flood watch through at least Thursday evening, with forecasters warning of minor concerns, including ponding on roads and flooding along small streams or in poor drainage areas.

Dangerous surf also will become a growing concern, with weather officials in the Bay Area warning of waves up to 26 feet high.

Thursday morning

By Thursday morning, showers will continue across Northern California, but the storm will take aim at Southern California and the Central Valley.

The heaviest rain in Los Angeles and Ventura counties is expected Thursday, with up to 2 inches in most areas — though only moderate rainfall rates are likely. Currently, no flood advisories have been issued for the regions.

However, a winter storm warning will be in effect beginning early Thursday for the Los Angeles, Riverside and San Bernardino county mountains, including the San Gabriels, where the highest elevations could get up to 2 feet of snow. A few inches of snow are possible as low as 4,500 feet, and forecasters are warning that “travel may be difficult to impossible,” including along the 5 Freeway corridor.

The southern Sierra expects heavy snowfall beginning late Wednesday and into Thursday — from 1 to 4 feet, depending on elevation — but heavy rainfall in the foothills could cause flooding and mudslides, the National Weather Service warned.

Farther south and east, across much of Orange, San Diego, Riverside and San Bernardino counties, a flood watch will go into effect Thursday morning and run through Friday. With a slight chance for thunderstorms all day Thursday, forecasters warn that “excessive runoff may result in flooding of rivers, creeks, streams, and other low-lying and flood-prone locations.”

Thursday night

Showers and bands of heavy rain will continue across southwest California, from the coast to the mountains.

Forecasters say snow levels will begin to drop Thursday night to about 4,500 to 5,000 feet, though heavy snow is not expected in those areas.

Friday

Much of the wind, flood and winter storm advisories will expire Friday, though lingering showers will remain in both Northern and Southern California.

Weekend

Saturday is expected to be a bit of a reprieve from precipitation — but officials say it won’t last long.

A second strong, wet storm, more focused on Southern California, is expected to bring more rain and snow, beginning as early as Sunday and lasting until midweek.