A powerful atmospheric river could bring "life-threatening floods" to California, with a total storm rainfall of 12 to 16 inches in some areas.
Earlier this week, a bomb cyclone churning over the Pacific ushered in atmospheric river conditions and winds equivalent to a hurricane when it hit the Pacific Northwest, killing at least two people and wreaking havoc in Washington, Oregon, California and British Columbia in Canada.
An atmospheric river is a narrow, but long, corridor of concentrated moisture in the atmosphere, often described as a "river in the sky." An example impacting northern California is expected to "remain relatively stationary over the next few days and produce an additional 6-12 inches of rainfall over regions with already saturated terrain," the National Weather Service (NWS) has said.
The atmospheric river's intensity is forecast to peak on Friday, leaving moderate bouts of rain throughout the whole day and lowering snow levels on Saturday.
"In the meantime, dangerous flooding, rock slides, and debris flows are likely, which has prompted a High Risk (level 4/4) of Excessive Rainfall to be issued across the northern California coastline today," the NWS said, so "be sure to check conditions before traveling and never drive across flooded roadways."
The NWS office Eureka in California has issued multiple flood watches across Northwest California, as "flooding caused by excessive rainfall continues to be possible" up until Friday evening.
The NWS update said: "Flooding may occur in poor drainage and urban areas. Low-water crossings may be flooded. Storm drains and ditches may become clogged with debris.
"Extensive street flooding and flooding of creeks and rivers are possible. Area creeks and streams are running high and could flood with more heavy rain."
The two known victims of the "bomb cyclone" that hit the West Coast include a woman who was killed on Tuesday, when a tree fell on a homeless encampment in Lynnwood, north of Seattle, Washington, and a second woman who died near Seattle after a tree fell on her home, Reuters reported.
Some 343,246 homes in Washington and 16,037 homes in California were without power, as of early Friday morning, according to poweroutage.us.
What Is an Atmospheric River?
Atmospheric reivers transport vast amounts of water vapor from tropical regions to other parts of the globe, sometimes stretching thousands of miles across the ocean.
When an atmospheric river reaches land, it can release heavy rainfall or snowfall, depending on the temperature. Newsweek has explained how they are formed here.
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