This week, the Northwest United States will see heavy rainfall and mountain snow as two storm systems nourished by an air river sweep in from the Pacific Ocean.
These atmospheric river systems transport heavy moisture from the central Pacific, bringing rain and snow to the afflicted areas.
As of Monday, moderate to heavy rain and high-elevation snow were falling across much of the Pacific Northwest, with precipitation moving inland and into northern California.
The initial storm is predicted to last until Tuesday, bringing continuous rain and snowfall to the region.
A second, more intense system will follow shortly after. It will hit the coast on Tuesday night and last until at least Wednesday, possibly longer.
The National Weather Service (NWS) says that the second wave will bring more rain and moisture, raising fears for isolated flooding and heavy snowfall in mountainous areas. Snow accumulations of up to 12 inches are expected in the Cascades, making travel dangerous in some high-altitude areas.
NWS meteorologist Anna Lindeman discussed how the atmospheric river fuels severe storms.
She explained to Newsweek that this happens when a “good moisture cap” emerges in the central Pacific, allowing tropical moisture to be brought in from far out in the ocean.
According to the NWS, typical atmospheric rivers convey the same volume of water vapor as the average flow at the Mississippi River’s mouth. However, powerful systems like these may move up to 15 times as much.
As the second system approaches, coastal locations, particularly Washington State, can expect several inches of rain, with the Olympic Peninsula receiving 4 to 6 inches. While totals in Oregon may be significantly lower, significant precipitation is still forecast.
“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 shared.
Though extensive flooding is not expected, the NWS is closely monitoring the Skokomish River in Washington, where water levels may rise due to 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 disclosed.
The NWS recommends folks in affected areas to keep an eye out for weather updates as the situation evolves. Lindeman emphasized the importance of caution on the road, especially in areas with standing water.
“If you see standing water on the roadways, don’t drive through it,” she told the audience. “You never know how deep it is, and it only takes six inches of water to completely wash away your vehicle.”
Lindeman advised drivers driving through hilly areas where heavy snow is forecast to pay attention to traffic signs and make sure their cars are fitted with chains if necessary.