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2 feet of snow? ‘Atmospheric river’ takes aim at West Coast.
The season’s first major “atmospheric river” storm is set to blast into the West Coast later this week and into the weekend, forecasters said, dumping heavy coastal rain and feet of mountain snow, potentially wreaking travel havoc for millions.
“The pattern setting up along the Northwest to northern California coast is indicative of an atmospheric river as the moisture can be traced back to Southeast Asia,” AccuWeather senior meteorologist Chad Merrill said in an online forecast.
This type of a pattern typically yields heavy rain and flooding, he added. In addition, the National Weather Service said that “another thing that will make weather headlines is the increase of heavy mountain snow from the Cascades to the northern Rockies, where 1 to 2 feet of snow is becoming more likely for the higher ranges.”
Travel is likely to be impacted by snow, rain and wind, the weather service said. “In addition to the potential for river flooding, small stream and urban flooding are possible.”
What’s the forecast?
The weather service said that areas from western Washington down through northern California face a risk of heavy rain later this week, with flooding possible over northern Washington to northwestern California. The worst of the heavy rain should be across northern California to southern Oregon.
Elsewhere, heavy snow is expected across high-elevation regions of the Cascades, northern Sierra Nevada, and Northern Rockies.
High winds are also forecast for western Washington to northern California. Inland, high winds are forecast for parts of Montana and Wyoming through the Four Corners.
The Northwest is forecast to see heavy rain and flooding over the next few days due to an atmospheric river storm.
What’s an atmospheric river?
Made visible by clouds, these ribbons of water vapor extend thousands of miles from the tropics to the western U.S. At 250 to 375 miles wide, they provide the fuel for massive rain and snowstorms that can cause flooding along the West Coast.
In general, atmospheric rivers pick up water vapor from the warm, moist air of tropical regions and then drop the water over land in cooler regions as rain or snow.
In fact, these “rivers in the sky” are responsible for up to 65% of the western USA’s extreme rain and snow events, a 2017 study said. And on average, up to 50% of the annual precipitation on the West Coast occurs in just a few atmospheric river events.
More: What is an ‘atmospheric river’? These rivers of water vapor can extend thousands of miles.
Some atmospheric rivers can stretch as far as 5,000 miles, all the way from Asia.
Though beneficial for water supplies, such events can wreak havoc on travel, bring deadly mudslides and cause catastrophic damage to life and property, the National Oceanic and Atmospheric Administration said.
“Atmospheric rivers are most common from November to January in the Northwest into Northern California,” Merrill said. “They also usually dump heavy rain in a short time period; within 24 hours, several inches can trigger flooding and mudslides.
“The upcoming late-week and early weekend storm will likely be no exception to that rule,” he added.
This article originally appeared on USA TODAY: ‘Atmospheric river’ to dump rain, snow on West Coast