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The daughter of former NOAA research scientist, Wenhao Dong, posed that exact question to her father when she was in first grade. "She was listening to the report about an atmospheric river over California," he recalled. "She asked me, 'Dad, do we have atmospheric rivers [in New Jersey]?'" That question partly motivated Dong and his collaborators to investigate how atmospheric rivers might be impacting the East Coast and West Coast differently. In a study published earlier this year in Nature that looked at 40 years of water vapor, precipitation and wind speed observations, Dong and his co-authors found that wintertime atmospheric rivers are growing significantly more frequent and intense over the Eastern U.S. while diminishing over the West. Their research showed that, over a 20-year period, atmospheric rivers could double the amount of rain falling in parts of the Southeast.

And while they might not produce as many headlines, East Coast atmospheric rivers are far from forgettable. One that hit New England at the end of 2024 left over 80,000 homes without electricity. But research into the phenomenon in the Eastern U.S. is limited. More than three-fourths of all atmospheric river studies focus on either the Western U.S. or Western Europe, Dong said. That bias makes sense because atmospheric rivers are the West's grand rainmakers, while hurricanes, large thunderstorms and Nor'easters dominate at least the news about Eastern weather. But the two coasts' big storms might have more in common than the headlines suggest.

"When you look at the data -- the precipitation contribution from [atmospheric rivers] -- you will see comparable contributions over the West and the Eastern U.S.," Dong said. Dong's team found that between 1980 and 2020, atmospheric river frequency over the Eastern U.S. increased by almost five percent each decade, with the storms slamming the South particularly hard. Parts of Mississippi, Alabama and Tennessee saw average atmospheric river rainfall rates increase by as much as two millimeters per day per decade over the last 40 years. With average daily precipitation in Mississippi being about 3.9 millimeters per day, if this trend continues, atmospheric rivers could double the average rainfall in some parts of the state in 20 years. Extreme rainfall rates in parts of Georgia have risen by almost four millimeters per day per decade, according to the study.

In the meantime, states such as Washington, Oregon and California have seen atmospheric river frequency decrease by nearly 4 percent per decade since 1980, the researchers found. This has led to long-term wintertime drying of the West Coast. Portland, Oregon, for example, has seen its average atmospheric river rain rate decrease by over two millimeters per decade. Its average daily rainfall over the past 20 years has been just over 2.5 millimeters. While the West is drying out overall, there is an increase in extreme precipitation events that are associated with catastrophic atmospheric rivers, Dong added.

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https://insideclimatenews.org/news/09082025/atmospheric-rivers-move-east/