Atmospheric River Poised to Strike US: Heavy Rain and Snow Expected

This week, the Northwest U.S. will experience significant rainfall and mountain snow as back-to-back storm systems fed by an atmospheric river sweep in from the Pacific Ocean.
These atmospheric river systems carry intense moisture from the central Pacific, delivering rain and snow to affected areas.
As of Monday, moderate to heavy rain and high-elevation snow is already falling across much of the Pacific Northwest, with precipitation spreading further inland and into northern California.
The initial storm is expected to linger through Tuesday, bringing steady rain and snowfall to the region.
A second, more intense system will follow closely behind. It will hit the coast on Tuesday night and persist until at least Wednesday and possibly beyond.
The National Weather Service (NWS) warns that this second wave will bring increased rainfall and additional moisture, raising concerns about isolated flooding and significant snowfall in mountainous areas. The Cascades could see snow accumulations of up to 12 inches, making travel hazardous in some high-altitude locations.
NWS meteorologist Anna Lindeman explained the role of the atmospheric river in fueling these storms.
She told Newsweek that this phenomenon occurs when a “good moisture cap” forms in the central Pacific, allowing tropical moisture to be drawn in from far out in the ocean.
Typical atmospheric rivers carry a volume of water vapor equivalent to the average flow at the mouth of the Mississippi River, according to the NWS. However, strong systems like this can transport up to 15 times that amount.
As the second system arrives, coastal regions, particularly Washington State, can expect several inches of rain, with the Olympic Peninsula forecast to receive between 4 and 6 inches. While totals may be slightly lower in Oregon, significant precipitation is still expected.
“It looks like they’re going to get a little bit less than that further South in Oregon, but we’re going to get some pretty hefty precipitation,” Lindeman said.
Though widespread flooding isn’t anticipated, the NWS is closely monitoring the Skokomish River in Washington, where water levels could rise with the heavy rains.
“We’re keeping an eye on how much rainfall we get and where the snow levels are because that will have a big impact on how much rivers rise,” Lindeman said.
The NWS advises residents in affected areas to monitor weather updates as the situation develops.
Lindeman stressed caution on roadways, particularly where standing water is present.
“If you see standing water on the roadways, don’t drive through it,” she said. “You never know how deep it is, and it only takes six inches of water to completely wash away your vehicle.”
For those traveling through mountainous regions, where heavy snow is expected, Lindeman urged drivers to heed road signage and ensure their vehicles are equipped with chains if needed.
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