A 5,000-mile conveyor belt of moisture called an atmospheric river has developed in the air over the Pacific Ocean, spanning from Asia to North America.
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Over the next several days, storms will move along this belt, bringing more than a foot of rain to parts of western Washington and northern Oregon and several feet of snow to the Cascade mountains. Gusty winds with these storms could reach 50 to 60 mph.
The National Weather Service has issued flood watches and high wind warnings for Washington state and Oregon.
An atmospheric river is a narrow but a long plume of moisture in the atmosphere, hundreds of miles wide and several thousand miles long. Atmospheric rivers transport up to half the West Coast’s precipitation each year during the rainy season, from October to April.
A single atmospheric river can carry more water than the earth's largest river, the Amazon.