Atmospheric River Soaking Northern California

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

Now, the newest atmospheric river is set to arrive in California later today with increasing threats of flooding, mountain snow and gusty winds. This is further south than most of the atmospheric river events so far this month, but gives a break to the Pacific Northwest.

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

Timing

Saturday night – Monday: The next atmospheric river arrives in Northern California late Saturday, stalls Sunday, and lingers Monday, especially north of the Bay Area.

Tuesday – Christmas Eve: A stronger storm will move into California with heavy rain and strong winds, first in Northern California, then spreading to Southern California Tuesday night. Some rain and mountain snow from this system could also stream into parts of Washington and Oregon.

Christmas Day: A second strong Pacific storm could surge into California, with a second round of heavy rain, strong winds and heavy Sierra snow that could linger into the day after Christmas.

(MORE: What Is An Atmospheric River?)

How Much More Rain, Snow

– Western Washington and Oregon: Up to an additional 2 inches of rain can be expected through Christmas week, with locally higher amounts in the coastal ranges, and foothills of the Olympics and Cascades below snow level. Parts of western Washington remain waterlogged from recent rounds of heavy rainfall.

– Northern California: Widespread 3-inch-plus rainfall totals through Christmas, with 8-inch-plus rainfall likely in the coastal ranges and foothills of the northern and central Sierra, below snow level. Parts of the Bay Area could see over 5 inches of total rainfall, which would equal over a month’s worth of rainfall for San Francisco. Flooding is possible.

– Southern California: Most of the L.A. Basin from Santa Barbara to Orange County are expected to pick up at least 3 inches of total rain during the Christmas week storms. Locally higher amounts are likely in the Southland mountains below snow level. San Diego County may also pick up an inch or so of total rainfall.

– Mountain snow: Several feet of Sierra snow is possible, mainly with the pair of storms during Christmas week. Elsewhere, over a foot of additional snow is likely in parts of the Cascades and northern Rockies.

Impacts

This heavy rain in California will likely trigger flash flooding and landslides, particularly in hilly and mountainous terrain and areas recently burned by wildfires. Be prepared to evacuate immediately if you live near a burned area. Long-duration flood watches are now in effect for Northern California and much of the Central Valley.

Strong winds with the Christmas week storms could down trees and knock out power, particularly in areas where the ground is soaked.

In western Washington and Oregon, this additional rain could prolong existing river flooding in some areas and could only increase the threat of landslides due to saturated ground.

Storm Recaps

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.

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.