Atmospheric: It’s Like Being Hit by 25 Mississippi Rivers


The Northwest received a climate warning twice during the first decade of the 21st century as atmospheric rivers of autumn arrived from the Pacific, dumped vast amounts of water in the Cascades, triggering floods that melted the early snowpack and wiped out much of the recreation infrastructure in national forests.

Climate study has focused on warm waters of the Caribbean and Gulf of Mexico triggering more powerful hurricanes, and wider tornado tracks across the Midwest.  Only lately has attention been devoted to the long, narrow jets of air that carry huge amounts of water vapor from the tropics to the Earth’s continental and polar regions. They can run 250-350 miles wide and contain the flow of 25 Mississippi Rivers.

Last month, a mighty atmospheric river scored a direct hit on Whatcom and Skagit Counties, the Fraser Valley, and southwest British Columbia.  It delivered a message summed up on CBC’s “The Fifth Estate” by Katherine Hayhoe, director of the Climate Science Center at Texas Tech: “Our infrastructure is designed for an Earth that no longer exists.” 

Want evidence? Look at the Coquihalla Highway, the main route linking the Lower Mainland to Interior B.C.  The atmospheric rivers of November destroyed five bridges, with 20 stretches damaged or washed out. For a time, Vancouver was cut off by land from the rest of Canada.

A 2017 NASA-led study found that atmospheric rivers which, in milder form, replenish water supplies and douse fires, will grow longer, wider and much more dangerous. In words of Duane Walister of the NASA Jet Propulsion Laboratory, “The results project that in a scenario where greenhouse gas emissions continue at the current rate, there will be about 10 percent fewer atmospheric rivers globally by the end of the 21st century. However, because the findings project that the atmospheric river will be, on average. About 25 percent wider and longer, the global frequency of atmospheric river conditions – like heavy rain and strong winds – will actually increase by about 50 percent.”

The term “Pineapple Express” dates to 1960, coined to describe storm systems stretching back from the Pacific Coast to Hawaii. They account for perhaps 30 to 50 percent of the West’s precipitation, triggering a majority of the West Coast’s floods. The new term, “atmospheric river,” has come as we learn more of the global extent of such aerial steams.  They come ashore in Portugal off the Atlantic Ocean and sweep into Chile’s mountains off the South Pacific. A study by the Scripps Institute of Oceanography and Army Corps of Engineers has found that 90 percent of the world’s moisture from the tropics and subtropics in transported by similar systems.

A “Kona Low” of unusual force struck this past week in Hawaii, seen on our weather maps as the origin of the Pineapple Express. The 50th state was hit with driving rains – as much as two feet – high winds plus blizzards atop Mauna Kea and Mauna Loa.  The Kona Low is itself an atmospheric river which can stall for days.  Hawaii’s state climatologist, Pao-Shin Chu, speculated that warmer ocean temperatures and a northward shift in the air stream – both consequences of climate change – might have intensified the storm.

University of Washington atmospheric sciences professor Cliff Mass has cast a skeptical eye on reporting of the floods of November. “It is both concerning and problematic that some local politicians, local and national media, and even some scientists, are willing to stretch the truth about the origins of this serious flooding event, suggesting a major contribution from global warming (frequently called climate change),” Mass wrote on his Weather Blog. “Society cannot effectively deal with environmental threats when it is provided with hyped or false information.”

Mass correctly points out that the hard-hit Sumas-Abbotsford area is “extraordinarily prone to flooding and has experienced flooding many times before.” (The Sumas prairie was once a lake until drained for agriculture.) He argues that there is “no evidence” climate change caused the recent inundation. He describes the November event as a “moderate atmospheric river” with no abnormally warm sea temperatures along its path across the eastern Pacific.

For those hit by it, however, the atmospheric river was hardly moderate. Its path was extraordinarily wide, inundating the town of Merritt, B.C., 100 miles north of Sumas, with landslides killing drivers on B.C. Rte. 99 north of Pemberton and Whistler.  The mountain-ringed town of Hope, at the head of the Fraser Valley, recorded 8.85 inches of rain.

Atmospheric rivers pose a threat to the snowpack on which the Northwest depends for electricity, irrigation and fisheries.  The snowpack gets major boosts in late fall and early winter from cold storms out of the Gulf of Alaska, such as hit the Cascades and Olympics last weekend.  A warm atmospheric river can wipe out the early snowpack. Its only upside is that by arriving in November, a TV “sweeps” month, television news can show salmon swimming along an inundated U.S. 101 near the Skokomish River.

The Pineapple Express experiences from 2003 and 2006 show what can happen when atmospheric rivers make landfall, particularly against a mountain range, and release their water vapor. The 2003 inundation did $13 million in damage in the front range of the Cascades. Gary Paull, longtime trails/recreation coordinator for the Mt. Baker-Snoqualmie National Forest, added up the damage: “Record flood on rivers from the south fork of the Stillaguamish north to the south side of Mt. Baker. Glacier Peak was the epicenter. Pacific Crest Trail bridges removed, damage to the White Chuck, Suiattle, and Mountain Loup roads.”

The 2006 atmospheric river hit the Stillaguamish again, but did its worst damage further south.  “This is the event that devastated Mt. Rainier National Park,” said Paull. The adjoining national forests suffered $5 million in road damage, $3 million in damage to trails.

The bills are increasing. Dr. Tom Corringham, staff research economist at the Scripps Institute of Oceanography, worked on the Scripps-Army Corps study. “We found that atmospheric rivers caused on average of $1.1 billion in flood damages yearly in the Western U.S.,” Corringham wrote recently in The Conversation. “More than 80 percent of all flooding damages in the West in the years we studied were associated with atmospheric rivers.  In some areas, such as coastal northern California, these systems caused over 99 percent of damages.” He added: “Our finding that damages increase exponentially with intensity suggests that even modest increases in atmospheric river intensity could lead to significantly larger impacts.”

The mechanisms are straightforward. Heat is trapped in the atmosphere by greenhouse gases, warming the Earth. This results in more water evaporating from oceans and increased moisture in the air makes storm systems grow stronger. “Like hurricanes, atmospheric rivers are projected to grow larger, wider and wetter in a warming climate,” writes Corringham.

Cliff Mass, while debunking alarmist news reports – he can’t abide Jay Inslee’s hyperbole —  does make an acknowledgement: “By the END of the century . . . aggressive global warming will increase the heaviest precipitation . . but that is in the future.” According to many of Mass’s peers, however, the future of more floods and melting snowpacks has already arrived. Where we live. The NASA-led study projected that frequency of the most intense atmospheric river storms will nearly double. We are in their path.

Joel Connelly
Joel Connelly
I worked for Seattle Post-Intelligencer from 1973 until it ceased print publication in 2009, and from 2009 to 6/30/2020. During that time, I wrote about 9 presidential races, 11 Canadian and British Columbia elections‎, four doomed WPPSS nuclear plants, six Washington wilderness battles, creation of two national Monuments (Hanford Reach and San Juan Islands), a 104 million acre Alaska Lands Act, plus the Columbia Gorge National Scenic Area.


  1. Thanks for this super-lucid picture of what’s going on overhead here and now, including the skepticism of Cliff Mass and the shifting terminology. You remind us that cause-and-effect are tenuous. So are facts and data from the past. Many climate change deniers—and even some skeptics—live in the Midwest, where my left-leaning mother grew up. She remembers a tornado in 1947 that cut neatly through her medium-small town, flattening the poor half and killing over 100 instantly—more than the total losses reported so far this year on her TV. I have no doubt the 1947 event really happened, but it was passed over by historians and scientists.


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