The Atmospheric Rivers: The Terrifying New Normal for California’s Extreme Weather

When the sky turns that specific shade of grey-green ahead of a major storm, a certain kind of dread descends upon Northern California. Anyone who has spent enough time there is aware of it. The air becomes dense. The hills appear nearly artificially verdant. Then there are times when the water just keeps coming for days, destroying roads, turning hillsides into sluggish brown rivers of mud, and swelling creeks into thunderous channels. That fear has been given a name more frequently than in previous winters. river in the atmosphere. Two terms that the majority of Californians had never heard before.

It’s possible that the term itself has caused an odd psychological shift, giving the storms a presence and identity similar to how naming a hurricane simultaneously makes it seem more real and menacing. However, something more tangible is also taking place. The intensity of these storms is increasing. Even casual news readers are beginning to pay attention to the science, which has been quietly developing for years.

In the last three years, Daniel Swain, a climate scientist at the University of California, has likely used the term “atmospheric river” more times than the majority of meteorologists do in a lifetime. He puts it simply: These events are what make or break California’s water situation. Five of them could roll in off the Pacific during a typical winter. Twenty could be seen in a wet winter. Each one is essentially a 300-mile-wide, one-mile-deep, and occasionally a thousand-mile-long corridor of concentrated water vapor in the lower atmosphere. They really do resemble rivers when viewed from a satellite. Big, slow, and unconcerned.
The frequency of the phrase is not the only thing that has changed. According to a thorough analysis that was published in the Journal of Climate, since 1980, the area that these events soak has grown by six to nine percent, their frequency has increased by two to six percent, and they are noticeably wetter than they were in the past. Lexi Henny, the lead author and atmospheric scientist who carried out most of the research while working at NASA, was cautious not to directly link all of that to climate change. She did point out, however, that the trend is very similar to what warming models have long predicted. More water vapor is held in warmer air. The fuel is water vapor. Even though the meteorology is complex, the math is not.

After atmospheric river research had quietly faded from scientific fashion in the early 2000s, Marty Ralph, director of the Center for Western Weather and Water Extremes at Scripps Institution of Oceanography, effectively brought it back to life. He assisted in demonstrating how to view these storms from the inside, not just as blobs on a radar screen but as dynamic, layered systems with predictable patterns, using improved satellite imaging and new aircraft-based data. His work paved the way for improved forecasting, and his name can now be found in almost every credible article about California’s winters. Additionally, he has argued that these storms have an impact far beyond the West Coast, causing historic snowfall in Alaska and influencing nor’easters on the East Coast.

The way California’s weather is framed has changed so much that it is difficult to ignore. Drought—years of unrelenting, grinding dryness that drained reservoirs and destroyed orchards—was the prevailing narrative for many years. When winter finally arrived in 2023, a sequence of atmospheric river storms piled on top of one another like freight trains on the same track. flooding in numerous counties. There were twenty-two fatalities. A portion of the Pacific Coast Highway was engulfed. Swift-water rescue teams and hundreds of other workers were dispatched throughout the state by the California Office of Emergency Services. “In one case it’s a deficit of atmospheric rivers,” Swain has stated, “and in the other case an overabundance — too many all at once.” It was chaotic, the destruction was real, and it didn’t feel like an anomaly. In a way, the drought was always a tale of insufficient storms. The floods tell a different tale. The opposite extremes of the same mechanism. Researchers also believe that the pendulum between those two poles is swinging more forcefully and quickly than it once did. The term “weather whiplash” has been used by meteorologists to describe the pattern that California is increasingly experiencing: punishing heat and dryness followed by abrupt, intense rain that parched ground and overloaded storm drains are unable to absorb. This is not hyperbole.

The way we discuss any of this has also evolved. Swain notes that phrases like “bomb cyclone” and “bombogenesis,” which many people thought were social media inventions meant to cause panic clicks, actually have their roots in military meteorologists who were advising Allied forces in the North Atlantic during World War II. The term “atmospheric river,” which was first used in a 1994 MIT paper, has a similar history. The choice made by science communicators and journalists to employ technically correct language rather than softening it is what is novel, not the phenomenon or even the terminology. Even though it occasionally seems like every storm now arrives pre-labeled for maximum alarm, that shift is probably good.

Nevertheless, considering what has already occurred, the alarm seems reasonable. Over 80% of flooding in the American West is caused by atmospheric rivers. They inflict damage worth a billion dollars annually on average. One such system struck British Columbia so hard in 2021 that an old glacial lake that had been drained for farmland almost a century earlier momentarily reappeared, with salmon and sturgeon swimming in areas that had been dry for decades. What the maps had forgotten, the land itself recalled. That picture keeps reappearing. Depending on which side of the barn you are standing on, it can be both breathtaking and extremely unsettling.

In order to improve forecast accuracy, Alex Padilla and Lisa Murkowski have introduced legislation in the U.S. Senate that would increase funding for airborne reconnaissance, which involves flying planes straight through these storms. Ralph thinks it might eventually be feasible to forecast atmospheric river impacts up to two weeks ahead of time, which would be a significant change in the way California handles its reservoirs, infrastructure, and emergency response. “The more we sample these storms,” he’s stated, “the more accurate the forecasts become.” The political will to support this kind of ongoing atmospheric science at the necessary scale is still up in the air. However, the argument is becoming more difficult to reject each time a new community is submerged.

For the time being, California continues to ride the seesaw: too dry, too wet, and then a protracted period of uncertainty as to what will happen next. There were always the atmospheric rivers. All they needed was for the world to warm up enough for them to be taken seriously.