Atmospheric rivers are drenching the West Coast with heavy rain, winds, and snow throughout the week, experts say, after the region evaded a brutal winter storm that slammed most of the United States over the holiday weekend.
The first in a week of storms is bringing powerful winds and flood risks from Washington state down to California Tuesday into Wednesday, according to the National Weather Service. All 11 states in the West are under weather alerts from the storm.
“Basically from Oregon southward into California is positioned right now in a place where a lot of moisture is being directed from the Pacific Ocean and it’s being directed right on into the terrain from the coastal ranges,” weather service meteorologist Richard Bann told USA TODAY.
Bann said the moisture will move from Northern California to the north of Los Angeles and continue into the Sierra Nevada, bringing a “decent amount of rain” that has been coming down since Monday night. Some places have already received up to an inch and a half of rain in an hour, according to Bann, which raises flash flooding concerns.
“It’s a very wet system,” Bann said.
The weather service said there were numerous reports of roadway flooding and downed trees as the storm moved through the San Francisco Bay Area early Tuesday. Pacific Gas & Electric’s website showed numerous power outages scattered across Northern California.
Winter storm warnings were also issued for the Sierra Nevada and motorists were advised that travel can be hazardous due to some ridgetop winds already hitting 120 mph.
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Path of the weather system
The storm will unleash heavy rain and mountain snow from Washington to California with rain showers moving southward into the middle of the week, AccuWeather said.
Numerous weather alerts — for heavy rain, snow, or wind — were issued by the weather service for most of central and Northern California. Coastal and central Oregon and Washington were inundated with flood watches and high wind warnings.
Following several waves of rain, snow, and ice across the Pacific Northwest, the storm will continue into the new year with as many as two more rounds of stormy weather possible, according to AccuWeather.
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The most powerful area of low pressure already arrived on Monday and spreading heavy rain inland into the Northwest and southward on Tuesday. As the rain moves southward, Los Angeles and San Diego are likely to be unsettled with rain late Tuesday into Wednesday, according to the weather service.
The weather service in Sacramento said a series of storms will impact Northern California through the week with a weaker system moving in Wednesday night into Thursday ahead of another strong storm Friday and Saturday.
Two to four inches of rainfall will be widespread along the West Coast, with one to two inches possible as far south as San Luis Obispo, California, AccuWeather reported. In addition to rain, wind gusts up to 60 mph will occur in western Washington, Oregon and, Northern California.
Over a foot of snowfall is also possible across the highest peaks of the Sierra Nevada by the middle of the week, according to AccuWeather.
What is an atmospheric river?
Atmospheric rivers have been said to be the cause of big weather issues along the West Coast during the winter. They are like “rivers in the sky,” according to the National Oceanic and Atmospheric Administration and are responsible for up to 65% of the western USA’s extreme rain and snow events, a 2017 study said.
Atmospheric rivers are ribbons of water vapor that can extend thousands of miles from the tropics to the western U.S. They are able to pick up water vapor from warm, moist air of tropical regions and then drop the water over land in cooler regions as rain or snow.
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Contributing: Doyle Rice, USA TODAY; The Associated Press