A series of systems aimed at the West Coast are expected to bring heavy rain and significant snowfall through the Christmas weekend.
An atmospheric river is providing ample moisture for a handful of fronts and low-pressure systems that will move across the region during the holiday.
Through Friday, the biggest concern is the potential for flash flooding across parts of Southern California. NOAA's Weather Prediction Center has placed areas from Irvine to San Diego in a slight risk for flash flooding, where as much as 3 inches of rain is possible.
A Flood Watch has been issued for parts of Southern California through Friday night.
Forecasters have warned of the potential for debris flows in areas scorched by wildfires during the summer. Evacuations have been issued for parts of those areas.
Throughout the holiday weekend, heavy snow is possible in the mountainous regions from Washington to California, where Winter Storm Warnings have been issued.
More than 5 feet of snow is possible in the Sierra Nevada through Christmas morning, with 1 to 4 feet possible in the other Western mountain ranges. This will make travel through many of the passes near impossible.
A blast of arctic air is expected to dive south behind the system and could bring subzero temperatures to parts of the Pacific Northwest next week.