AccuWeather meteorologists are forecasting that at least four significant storms, fueled by Pacific moisture, will impact the West Coast through the end of next week, raising the risk of flooding and mudslides.
Although not all storms are expected to develop into bomb cyclones, each will bring substantial rainfall from Northern California to western Washington, with totals potentially reaching up to 2 feet.
The storms will continue through the Friday after Christmas, particularly affecting the west-facing slopes of the mountains.
One or more of the storms is anticipated to form an atmospheric river, which could bring intense rainfall or heavy snowfall to portions of the West Coast, according to AccuWeather Senior Meteorologist Brett Anderson.
The heaviest rainfall will occur along the Interstate 5 corridor, stretching from near San Francisco and Sacramento in California to Eugene and Portland in Oregon, and Seattle, Washington.
This heavy rainfall will also extend to Vancouver, British Columbia. Motorists should expect difficult driving conditions, including potential ponding on roads in areas with poor drainage.
The storms’ significant rainfall will increase the likelihood of flash flooding, particularly in smaller streams.
As runoff builds with each storm, river flooding, especially in short-run rivers from the Olympic, Cascade, Siskiyou, and Coast Ranges, will become more likely.
The risk of mudslides and debris flows will rise, especially in areas affected by recent wildfires, as saturated soil may cause landslides.
Snow levels will fluctuate with each storm. Initially, snow levels will remain high, above mountain passes, but colder storms with lower snow levels are expected to arrive during the week of Christmas.
This will bring wintry travel conditions to mountain areas, including Donner Pass, California, and Snoqualmie Pass, Washington. Motorists are advised to monitor forecasts closely and be prepared for rapidly changing conditions.
In the high country of the Cascades and northern Sierra Nevada, up to 10 feet of snow could accumulate, increasing the risk of avalanches.
Southern California is expected to remain largely unaffected by the storms, with dry and mild conditions expected in Los Angeles and San Diego.
However, those traveling north to visit family over the holidays should prepare for worsening conditions near and north of I-80.