Atmospheric rivers to continue affecting Pacific states through late December amid La Niña pattern
A series of atmospheric rivers are forecast to continue impacting the Pacific Northwest and spread southward into California through late December. Moderate risks of heavy precipitation, snow, and high winds are forecast across the West Coast between December 20 and 26, 2025.
Image credit: SNFD #4
A mid-level ridge over the Bering Sea and a downstream trough in the northeastern Pacific are increasing the potential for atmospheric river impacts during the last week of December.
Historic floods have already swept across western Washington and northwestern Oregon, with rising river levels and saturated soils expected to persist into at least late December. These conditions will add to the risk of additional flooding and landslides with further precipitation later in the season.
The CPC’s Week-2 U.S. Hazards Outlook shows a moderate risk 40–60% probability of heavy precipitation from western Washington through west-central California during December 20–26. Another moderate risk for heavy rainfall extends from west-central California to the Mexican border between December 22 and 26.
Heavy snowfall is also anticipated across the Cascade Range and Sierra Nevada, where a 40–60% probability of heavy snow is indicated for December 20–26.
Enhanced onshore flow is forecast to generate strong winds along much of the West Coast and northern Interior West, with the highest gusts expected near coastal and high-elevation areas.
During this period, there is a greater than 60% probability of above-normal precipitation from northern and central California into southeastern Oregon and northern Nevada. The probability remains above 50% from northern and central Oregon into southern California.
The CPC notes that the prevailing La Niña pattern and periods of enhanced onshore flow are likely to persist into the New Year, maintaining favorable conditions for continued storm activity across the Pacific states.
References:
1 Key Messages for Atmospheric Rivers, Flooding, and High Winds in the Pacific Northwest and California – NOAA/CPC – Updated on December 12, 2025
I am an Assistant Editor and Severe Weather & Science Journalist at The Watchers, specializing in real-time severe weather coverage, geophysical event reporting, and research-driven scientific analysis. You can reach me at rishav(at)watchers(.)news.
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