A succession of Pacific storms, fueled by atmospheric rivers, is poised to impact the West Coast through the Christmas holiday, bringing persistent heavy rainfall from already saturated regions of Washington and Oregon down into California. Flood watches remain active across much of California through the Friday following Christmas, as repeated rounds of precipitation show no signs of abating.
The latest atmospheric river event elevates concerns for flooding, significant mountain snowfall, and powerful winds. Unlike many recent events this month, the most severe effects are anticipated further south, offering some relief to the still inundated Pacific Northwest.
Forecast Timeline
Sunday to Monday: An atmospheric river affecting Northern California, which started Saturday, will intensify and stall from Sunday into Monday, particularly in areas north of the Bay Area.
Tuesday to Christmas Eve: A more potent storm system will arrive in California, delivering heavy rain and strong winds initially to Northern California before extending to Southern California by Tuesday night. Flash flooding poses a major threat. This system may also bring some rain and mountain snow to portions of Washington and Oregon.
Christmas Day: A second robust Pacific storm could reach California, bringing another wave of heavy rain, strong winds, and substantial Sierra Nevada snowfall that may persist into the day after Christmas.
Expected Precipitation
Western Washington and Oregon: Up to an additional 2 inches of rain is possible through Christmas week, with higher localized amounts in coastal ranges and the foothills of the Olympics and Cascades below snow level. Some areas in western Washington remain waterlogged from recent heavy rains.
Northern California: Widespread rainfall totals exceeding 3 inches are expected through Christmas, with potential for over 12 inches in coastal ranges and the foothills of the northern and central Sierra Nevada below snow level. Parts of the Bay Area could receive over 5 inches, equating to more than a month's typical rainfall for San Francisco, raising flood risks.
Southern California: Areas from Santa Barbara to Orange County in the Los Angeles Basin are likely to see at least 3 inches of total rain during the Christmas week storms. Higher amounts are possible in the mountains of Southern California below snow level. San Diego County may also accumulate around an inch of rain.
Mountain Snow: Several feet of snow are possible in the Sierra Nevada, primarily from the two storms during Christmas week. Additionally, over a foot of new snow is likely in parts of the Cascades and northern Rockies.
Potential Impacts
The heavy rainfall in California is expected to trigger flash flooding and landslides, especially in hilly, mountainous terrain, and regions recently affected by wildfires. Residents near burned areas should be prepared for immediate evacuation. Extended flood watches are currently in effect for Northern California and much of the Central Valley.
Rainfall at higher elevations than usual in these atmospheric river events could melt existing snowpack, exacerbating flash and river flooding threats.
Strong winds accompanying the Christmas week storms may topple trees and cause power outages, particularly in areas with saturated ground.
In western Washington and Oregon, additional rain could prolong existing river flooding in some locations and increase landslide risks due to already waterlogged soils.
Recent Weather Events
The West has endured a severe stretch of weather recently. Record flooding initially struck parts of western Washington. As affected areas began recovering, a powerful windstorm swept through much of the Northwest and Rockies on Wednesday, with gusts reaching up to 144 mph and over 160 reports of wind damage across Washington, Oregon, Idaho, Montana, Wyoming, and Colorado.
Spokane, Washington, recorded a wind gust of 75 mph on Wednesday afternoon, the second-highest known for the city. The Spokane River is flowing much higher than normal due to 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 home sustained significant damage from a fallen tree.
In Idaho, two children were seriously injured by falling trees while waiting for a bus in Twin Falls on Wednesday morning. Local reports also indicate one fatality in northern Idaho when a tree struck a 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 areas are still recovering from 10 to 18 inches of rain during last week's series of atmospheric rivers.
This led to two levee breaches in King County: one along the Green River in Tukwila, east of SeaTac Airport on Monday, and another early Tuesday morning in the town of Pacific, east of Tacoma.
