Atmospheric Rivers Will Spread Flood Threat To Oregon, California, After Soaking Washington State

More Rain, Snow, Flooding For Pacific Northwest

A parade of Pacific storms accompanied by atmospheric rivers continues to march into the West Coast through Christmas week, spreading the threat of heavy rain from already flooded areas of western Washington to Oregon and California.

To say it's been a terrible stretch of weather in parts of the West has been an understatement.

First, record flooding hit parts of western Washington. Then, as flood-ravaged areas were recovering, a powerhouse windstorm blasted much of the Northwest and Rockies on Wednesday, with winds clocked up to 144 mph and over 160 reports of wind damage in Washington, Oregon, Idaho, Montana, Wyoming and Colorado.

(LATEST NEWS: Hundreds Of Thousands Lose Power In Northwest)

Now, another atmospheric river is pushing into the West, as the radar below shows.

Let's step through the timing, then who could see the most rain and the potential impacts.

Timing

Friday: The atmospheric river shifts into southern Oregon and Northern California, then weakens by the evening. The main impacts will remain mainly north of the Bay Area. Showers and mountain snow may linger in Washington, northern Oregon and the northern Rockies.

Saturday night - Monday: The next atmospheric river arrives in Northern California Saturday night, may intensify Sunday, and linger Monday, especially north of the Bay Area.

(MORE: What Is An Atmospheric River?)

How Much More Rain, Snow

Much of southwestern Washington, western Oregon and Northern Calfornia should pick up at least another 3 inches of rainfall through Monday. In the Bay Area, the best chance of heavy rain will be in the North Bay, including Marin, Napa and Sonoma Counties.

Higher totals are likely in the coastal ranges and foothills of the Oregon Cascades, Siskiyous and Sierra, as the map below shows.

Meanwhile, over a foot of snow is likely in parts of the Washington Cascades into the northern Rockies, along with the highest elevations of the Sierra Nevada.

Impacts

This heavy rain will likely trigger flash flooding and some landslides, particularly in areas recently burned by wildfires. Rain will also fall at higher elevations than usual in these atmospheric river events, potentially melting existing snowpack adding to the threat of flash and river flooding.

Some urban flash flooding is also likely in the Portland-Salem-Eugene, Oregon corridor, as well as in parts of the Bay Area, especially Marin, Napa and Sonoma Counties.

In southern parts of western Washington, this additional rain may keep rivers in minor to moderate flooding longer, including stretches of the Cowlitz, Green and White Rivers.

Any End In Sight?

Unfortunately, the rest of Christmas week still looks active in the West.

The atmospheric conditions, including a mid-level ridge over the Bering Sea and a downstream trough in the northeastern Pacific, will serve as a sort of an atmospheric nozzle that will likely steer additional moisture to the already waterlogged West Coast.

Computer forecast models suggest a strong Pacific storm could surge into California Tuesday, and its heavy rain could also spread to Southern Callifornia and the Desert Southwest into Christmas Eve.

If that isn't enough, another wet storm could arrive in California later on Christmas Day or the following Friday.

If there's a bit of good news, it's that the heaviest rain may not target waterlogged, flood-ravaged western Washington Christmas week. And any precipitation that falls there may be more "typical" Cascades snow, not rain, helping to replenish snowpack that melted away during the recent record flooding.

Storm Recaps

Spokane, Washington, recorded a wind gust of 75 mph on Wednesday afternoon. That is the second-highest known wind gust for the city. The Spokane River is also raging much higher than normal due to all the recent precipitation.

In nearby Pullman, Washington, widespread damage to trees, power lines, and traffic signals was reported along with a wind gust up to 81 mph. At least one house reported significant damage due to a downed tree.

In Idaho, two kids were seriously injured Wednesday morning by falling trees while waiting for the bus in Twin Falls. Local media is also reporting that one man was killed in northern Idaho when a tree crashed into his home.

An atmospheric river earlier this week dumped 2 to 5 inches of rain in the Cascades and Olympics of Washington state, with an additional 2 to 5 inches on Tuesday. These are the same areas that are still recovering from 10 to 18 inches of rain during last week's procession of atmospheric rivers.

This led to a pair of levee breaches in King County, one along the Green River in Tukwila, just east of SeaTac Airport, Monday, then early Tuesday morning in the town of Pacific, east of Tacoma.

(MORE: Evacuations Prompted From Washington Levee Breaches)

Jonathan Belles has been a digital meteorologist for weather.com for 9 years. His favorite weather is tropical weather, but also enjoys covering high-impact weather and news stories and winter storms. He's a two-time graduate of Florida State University and a proud graduate of St. Petersburg College.