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Parts of the West will be facing days of heavy rain and snow as an “atmospheric river” comes in from the Pacific Ocean, forecasters say.
What is an atmospheric river, what does it do and when will it end? Here’s what we know about it.
What is an atmospheric river?
An atmospheric river is a fast-moving storm system that is a stream of water vapor moving through the sky.
The systems carry water vapor from the tropics and are common in the U.S. during winter.
According to the National Oceanic and Atmospheric Administration, atmospheric rivers are about 250 to 375 miles wide and can be more than 1,000 miles long.
What does it do?
Atmospheric rivers flow in the direction of moving air created by weather systems. As the atmospheric river moves over the land, it drops excessive rainfall or snow at higher elevations. It causes flash flooding, mudslides and debris flows, according to the National Weather Service.
When will it end?
As of Tuesday evening, 2 to 6 inches of rain had fallen in the hardest-hit areas of the West Coast. More than 128,000 customers were without power in Oregon, along with nearly 40,000 in Washington early Wednesday, according to poweroutage.us.
According to the NWS, the system was expected to continue to produce unsettled weather through the weekend.
Heavy rain will move across the West Coast and parts of southern/central California, and heavy snow is possible throughout the higher elevations of the Sierra Nevada, the Cascades, and the northern and central portions of the Rockies, according to the NWS.
More than 128,000 customers were without power in Oregon, along with nearly 40,000 in Washington early Wednesday, according to poweroutage.us.
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