An atmospheric river will deliver heavy rain, scattered flooding, and gusty winds from the Pacific Northwest through the northern Great Basin and Rockies in the coming days, the National Weather Service (NWS) has forecast.
Why It Matters
The NWS warned that by Sunday over the Interior Northwest, rain combined with snowmelt will increase the risk of flood hazards.
An atmospheric river will bring chances for flooding to the Pacific Northwest pic.twitter.com/xUPjyGFrvE
— NWS Weather Prediction Center (@NWSWPC) February 22, 2025
What To Know
An NWS forecast map issued on Saturday showed that there was a “marginal” (5 to 15 percent) chance of excessive rainfall leading to flash flooding in parts of western Oregon, western and eastern Washington, northern Idaho, and western Montana on Sunday.
There was a higher—”slight”—chance of 15 to 40 percent for isolated parts of western Oregon and Washington, including the former’s coast.
A portion of northwestern California could also be impacted, it showed.
On Monday, the map suggested the flooding risk area would be reduced primarily to the westernmost areas of Oregon and Washington.
“Three to 5 inches of rainfall is forecast across the region for Saturday-Monday,” the NWS said. “Favorable areas in terrain may see as much as six to 10 inches of rainfall.”
Flood-related warnings were in place from the NWS across Oregon and Washington, as well as Idaho, Montana, Wyoming, and North Dakota as of Sunday morning.
The NWS said flooding would be possible in Montana’s Flathead, Lake, Lincoln, Sanders, Granite, Mineral, Missoula and Ravalli Counties.
Flooding was also possible in Clearwater and Idaho Counties in Idaho, it said.
Portions of northwest and west central Washington, could also see floods, including Grays Harbor, Skagit, King, Lewis, Pierce, Snohomish and Thurston Counties.
The National Oceanic and Atmospheric Administration (NOAA) describes atmospheric rivers as long, narrow bands in the atmosphere that transport large amounts of water vapor outside the tropics.
Although their size and strength can differ widely, on average they transport a volume of water vapor comparable to the flow of the Mississippi River at its mouth.
Exceptionally strong atmospheric rivers can transport up to 15 times that amount. When they make landfall, they typically release this moisture as rain or snow.
What People Are Saying
NWS Portland, Oregon, said on X, formerly Twitter, Saturday: “Our next round of rainfall is gearing up to move into the region. We have three distinct periods of rain coming through. This afternoon through tonight. Sunday late morning through evening, and then again on Monday.”
NWS Seattle said on X on Saturday: “Steady rain will continue across western Washington through tonight. The heavy rain, combined with warmer temperatures, will allow for rivers to continue to rise. A flood warning is currently in place for the Skokomish River in Mason County.”
What Happens Next
At the time of writing, the latest flood advisory for the area—issued when conditions are favorable for flooding—was in place through Tuesday night.
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