For people on the West Coast, the weather phenomenon that can bring heavy rain and snow from the atmospheric river, San Diego, to Vancouver is just as wintery as it is in Boston.
Like these East Coast storms, “Atmosphere River” can feel like a buzzword. Even if it's the way that most people walking on the streets of San Francisco experience it, it can attract more attention than mere “heavy rain.” But it is also a specific weather phenomenon that explains moisture-rich storms that occur in the Pacific Ocean and dumps precipitation when colliding with the mountain ranges of Washington, Oregon and California.
However, these plumes of extremely humid air transported through the atmosphere by strong winds are not endemic to the West Coast. They occur all over the world, and more and more meteorologists and scientists are beginning to apply the term to storms east of the Rocky Mountains. This spring, Accuweather locked in the unusual weather on the “Atmosphere River” when heavy rain days caused fatal floods in central and southern United States. So did CNN.
Some researchers hope that the term will be adopted more widely, but not all meteorologists, including the National Weather Service, do this. At the heart of the debate is the struggle over how predictors will explain the weather for the day.
The Ati River can extend up to 2,000 miles.
They generally form above the oceans in tropical and subtropical areas, where water evaporates and gathers in huge air streams of steam, moving through the lower atmosphere towards the Arctic and Antarctic. They are clearly narrow, averaged 500 miles wide and extending to 1,000 miles. While many weak atmospheric rivers bring about beneficial rain and snow, strong rivers can cause heavy rain that causes flooding, landslides and catastrophic damage.
The rain isn't all. Just as water needs to be squeezed from wet sponges, rivers in the atmosphere need a mechanism to release rain and snow. As the atmospheric rivers are pushed upwards, the water vapor cools, condenses, and settles.
On the West Coast, this process occurs again and again from late autumn to early spring, and is easy to understand as mountain ranges such as the Cascade and Sierra Nevada provide its upward lift. Atmospheric rivers coming from the Pacific Ocean hit mountains, causing water vapor to rise and turn into liquid.
It is more complicated in other parts of the country, and upward lifts usually come from less specific and less predictable atmospheric instability than mountains. In early April, in the central US, cold air descending from the north ploughed under the Atmospheric River coming from the bay, pushing up the wet, moist air.
“If warm air is lifted to a point where it gets warmer than it's surroundings, it can explosively rise, which can lead to serious thunderstorms,” said Travis O'Brien, an assistant professor at Indiana University, co-authored a paper that attracted attention last year in Atmospheric Rivers on the Midwest and East Coast.
Floods were extreme in places like Kentucky, Tennessee and Arkansas (where more than 15 inches of rain were recorded).
Anyway, why did they call it?
Atmospheric rivers have always been present, but scientists began to recognize them in the mid-1970s and 1980s with the development of a global operating environment satellite called Goes, built by NASA and operated by the National Maritime and Atmospheric Administration.
Clifford Masa, professor of atmospheric science at the University of Washington, said: “Before that, we didn't talk much about it.”
Advanced satellite technology provided images that allow researchers and meteorologists to see the atmospheric rivers. They began talking about them and gave them a name.
The term Ati River was first published in the 1990s by two men at the Massachusetts Institute of Technology: Reginald E. Newell, a meteorologist and professor, and research scientist Yong Zhu. They first used the term tropospheric river after the lowest layer of the Earth's atmosphere, where most weather occurs. Two years later it transformed into an atmospheric river. This is the explanation the river chose to “carry about the same amount of water as the Amazon.”
Are you using the terminology too much? sometimes.
It was not until the 2010s and 2020s that the term came into the mainstream, but almost exclusively on the West Coast. This is because scientists were closely following and studying the atmospheric rivers of universities. This is because hundreds of research papers have identified them as the main source of rain and snow, and are almost singular sources of the great floods in California, Oregon and Washington. One amazing example: A series of nine atmospheric rivers that drenched California in December 2022 and January 2023, causing widespread flooding for weeks and alleviating drought.
Daniel Swain, a climate scientist at the University of California, Los Angeles, is known for his popular commentary on meteorology, but interest in atmospheric rivers is generally surged during California's extremely wet storms. He likes labels but sometimes misused and said he's used too much. Media can mislead the public if they don't distinguish between rivers of inconspicuous atmosphere, medium rivers that bring beneficial rainfall, and even mild rivers that destroy even more scary rivers.
“The only real pitfall is the concept that every atmospheric river is truly an extreme and destructive event, because of course that's not true,” Swain said.
To mitigate this confusion, it was announced in 2019 that atmospheric rivers will be categorized. Dr. Marty Ralph, director of the Scripps Institute of Oceanography in San Diego and the Center for Extreme Weather and Water in the West, led development on the scale of the West Coast, applying it in other parts of the world, including the Arctic and Antarctic. He has primarily promoted research and marketing the term atmospheric river, particularly in California. He and his team have written dozens of papers.
“It was Marty Ralph who organized the scientific community around this idea that Atmosphere Rivers is a phenomenon worth studying, and I think his excellence has implicitly linked people to the West Coast, despite the original research being a global study,” Dr. O'Brien said.
The association, or its association, is fooled by the daily forecasts that the West Coast offices of the West Coast offices generally discuss atmospheric rivers, but offices in other parts of the country are not.
“We don't usually describe it that way in the Midwest and Southeast,” said Jimmy Barham, a lead meteorologist with the Arkansas Meteorological Service. “We're just going to say higher-level moisture.”
The emphasis on the West Coast also means that hurricanes and summer thunderstorms are also major rainmakers, meaning that atmospheric rivers are less studied in other parts of the country that has attracted much attention.
Dr. Ralph hopes that the research will expand to the East Coast.
“Inside Big No East, it often lurks in very strong, if not very strong, atmospheric rivers,” he said.
