What is an atmospheric river? Powerful storm to drench California

Science and Innovation

A powerful atmospheric river could bring multiple inches of rain to central and southern parts of California.

California residents, brace yourselves: an atmospheric river could bring multiple inches of rain to central and southern parts of the state over the next few days.

Read on for a look at the meteorological phenomeonon — and what to expect from the storm.

“Rivers in the sky”

An atmospheric river is a huge plume of subtropical moisture.

“Atmospheric rivers are relatively long, narrow regions in the atmosphere – like rivers in the sky – that transport most of the water vapor outside of the tropics,” the National Oceanic and Atmospheric Administration (NOAA) says.

“When the atmospheric rivers make landfall, they often release this water vapor in the form of rain or snow,” according to the agency.

They may also bring severe precipitation and destruction, though “most are weak systems that often provide beneficial rain or snow that is crucial to the water supply.”

The NOAA says atmospheric rivers are typically 250 to 375 miles in width.

What’s going on with California?

The National Weather Service (NWS) Los Angeles tweeted Tuesday that the atmospheric river event was happening.

“Heavier rain expected tonight into Thu with Flash Flood Watch in effect for recent burn areas,” it said.

The agency said in another tweet that coasts and valleys could get two to six inches of rain, with foothills and mountains getting five to 10 inches.

As many as 30,000 people have been ordered to leave communities by noon on the south coast of Santa Barbara County, where a Jan. 9 deluge unleashed deadly debris flows into Montecito.

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