In an unusual climatic twist, Washington state has been drenched with nearly 5 trillion gallons, or 19 trillion liters, of rain over the past week. Meteorologists attribute this deluge to warm air and water, alongside peculiar weather conditions that date back to tropical cyclone flooding in Indonesia. These factors have intensified atmospheric rivers, which are now threatening to push flood levels to record highs.

Experts warn that the most severe and persistent rains will continue to batter the region until late Thursday or early Friday. After this, the intensity is expected to decrease slightly, though the West Coast is unlikely to find any respite from this relentless “fire hose” of moisture until the week of Christmas, according to Matt Jeglum, the acting science chief for the National Weather Service’s western region.

Atmospheric rivers, which are long, narrow channels of water vapor formed over oceans, transport moisture from tropical areas to northern regions. The Pacific Northwest, more than any other part of the West Coast, typically experiences a few dozen of these each year. However, meteorologists note that the current systems are unusually large and potent.

The combination of Wednesday’s torrential downpours and Monday’s rains has led to predictions of record-breaking floods, particularly along the Skagit River in northern Washington, which eventually empties into the Puget Sound, as explained by Washington state climatologist Guillaume Mauger.

Ryan Maue, a former chief scientist at the National Oceanic and Atmospheric Administration and now a private meteorologist, highlighted the severity of the situation. “The atmospheric rivers, the ARs, are continually reloading,” he said, suggesting that the region could receive an extraordinary 20 to 30 inches (51 to 76 centimeters) of rain over this three-week period, marking an extreme weather event.

Maue added: “I wouldn’t want to live there. Not right now.”

Using rain gauge observations, Maue estimated almost 5 trillion gallons — more than enough to fill Oregon’s Crater Lake or more than 18,000 Empire State Buildings — fell in the area over the past week. One weather station at Mount Rainier measured 21 inches (53 centimeters) of rain since Thursday, Jeglum said.

“Those numbers are big, but are not unheard of,” Mauger said.

The moisture originated a few hundred miles north of Hawaii, where the Pacific is a couple degrees warmer than normal. That fuels the atmospheric river even more and then warmer air adds to that, said meteorologist Jeff Masters, co-founder of Weather Underground and now at Yale Climate Connections. Because it’s so warm, a lot more of that moisture is falling as rain than snow, he said.

These storms “have been supercharged by the chain of events that began two weeks ago” much farther west than Hawaii, Maue said.

He pointed to an area near Indonesia that saw deadly flooding from tropical cyclones. That coincided with a natural season weather pattern that moves around every 30 days or so — the Madden Julian Oscillation — which Maue said was the strongest it has been this time of year in decades. It sent out waves that helped carry an “unbroken line of moisture” and energy from the Indonesia event toward the Americas. A high-pressure ridge off the California coast pushed the atmospheric river system north, further funneled by unusual warmth over Russia and cold over Alaska.

And Washington became the bullseye.

In a world made warmer by the burning of coal, oil and natural gas, atmospheric river storms will be bigger and wetter, according to studies, computer models and meteorologists. A study earlier this year found that may already be happening. Looking at events since 1980, researchers calculated that the storms have increased in the area they soak by 6% to 9%, increased in frequency by 2% to 6% and are slightly wetter than before.

A quick analysis by Climate Central looking at the heavy rain found that ocean temperatures under the atmospheric rivers are 10 times more likely to be warmer than normal because of human-caused climate change. Air temperatures in the Pacific Northwest are much warmer than normal, and that’s four to five times more likely because of climate change, said Climate Central meteorologist Shel Winkley.

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