What is an “atmospheric river”?

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Dear Tom,

What is an “atmospheric river”?

Thanks, Joy Hajduk-DeGraff

Dear Joy,

According to NOAA, the parent agency of the National Weather Service, atmospheric rivers are flowing columns of water vapor identified by satellites, and are responsible for generating large amounts of rain and snow. They are usually about 250-375 miles wide and found in the lower levels of the atmosphere, often around 5,000 feet. They are a major feature of the global water cycle and are found throughout the world. In the U.S. they are responsible for up to 50 percent of the annual precipitation on the West Coast. Precipitation is produced due to orographic lift when column of moisture moves onshore and is lifted and cooled as it interacts with mountain ranges. The strongest ones can produce extreme amounts of rain and snow causing widespread flooding and travel disruption.