A “series” of atmospheric rivers is set to bring significant precipitation and turbulent weather to the western United States this week, according to the National Weather Service (NWS).
These events, described as “rivers in the sky,” will channel moisture from the Pacific Ocean inland, delivering heavy rain, mountain snow and potential disruptions across multiple states.
Monday’s Focus: Oregon, Northern California and the Rockies
The NWS forecasts that the heaviest precipitation on Monday will target areas from Oregon and northern California to central Idaho and northwest Wyoming.
Coastal rain and mountain snow are already affecting the region, with snowfall totals of 4—8 inches common in higher elevations and over a foot expected for the southern Cascades in Oregon.
Justin Sullivan //Getty
A coastal flood advisory is in effect until 10 a.m. PST on Monday for parts of Washington, including San Juan, Western Whatcom and Western Skagit counties.
Another advisory, issued by NWS’s Seattle office, is in place until 4 p.m. PST in the Central Coast Zone.
The advisories warn of minor coastal flooding, urging travelers to avoid driving through water and to heed road closures.
Newsweek contacted the NWS office in Seattle via email outside of working hours for further comment.
Tuesday Brings a Shift Northward
By Tuesday, the atmospheric river’s focus will move north, delivering heavier rain to coastal Washington and intensifying snowfall in the northern Cascades, the NWS predicts.
Atmospheric rivers bring crucial precipitation to the region’s water supply, although they also pose risks of localized flooding, mudslides and travel hazards.
The Week Ahead: Precipitation will favor the Pacific Northwest and northern CA as a series of atmospheric rivers push inland. Dry conditions are expected from the Desert Southwest to the central Plains, with unsettled weather in store from the southern Plains to the Northeast. pic.twitter.com/pO3MYgqZWO
— NWS Weather Prediction Center (@NWSWPC) December 15, 2024
Understanding Atmospheric Rivers
Atmospheric rivers are narrow bands of concentrated water vapor in the atmosphere. A single atmospheric river can transport as much moisture as the Mississippi River at its mouth, and stronger systems may carry up to 15 times that amount, according to the National Oceanic and Atmospheric Administration (NOAA).
According to the U.S. Department of Energy, atmospheric rivers are responsible for about 50 percent of the West Coast’s annual water supply and ended three-quarters of droughts in the region between 1950 and 2010.
An analysis from the Center for Western Weather and Water Extremes earlier this year found that a total of 51 atmospheric river systems made landfall over the West Coast between October 2023 and March 2024.
At any one time, there could be five active atmospheric rivers on the planet, pulling moisture up from the tropics.
Safety Warnings and Future Outlook
The NWS has advised residents to prepare for hazardous travel conditions, avoid flood-prone areas, and monitor official updates. Coastal flood impacts are expected to coincide with high tide Monday morning, potentially inundating roads and parking lots.
Meanwhile, forecasters at AccuWeather are warning that more severe weather is likely on the way.
“While a break in the busy pattern is expected for midweek, another series of storms ramps back up again into this upcoming weekend and early the following week,” one AccuWeather meteorologist said in a statement.
The heavy rain and snow come on the heels of earlier atmospheric rivers, which have already delivered dramatic weather to California, including a rare tornado warning in the Bay Area over the weekend.
In Scotts Valley, suspected tornado activity overturned cars and caused wind gusts up to 83 miles per hour.
This week’s activity may not be as impactful as storms that have slammed the West in recent weeks.
“It’s not the telltale traditional atmospheric river like the one we saw in late November where it stalls and remains stagnant,” Dalton Behringer, a meteorologist for the National Weather Service’s Bay Area office, told SF Gate.
He added: “We’re officially in the rainy season. Make sure to heed any existing road closures and don’t drive around barricades.”
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