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With the season’s first “atmospheric river” expected this week, the Bay Area prepares to take a dip

A primer on the meteorological watercourse heading our way

Pat May, business reporter, San Jose Mercury News, for his Wordpress profile. (Michael Malone/Bay Area News Group)
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Last winter, it wasn’t until January that Northern California saw that first ribbon of wetness known as an “atmospheric river” roll in from Hawaii, hitting the region like some super-sized dunking booth.

This year, the river’s not waiting in the sidelines. On Wednesday, we’re expected to receive the season’s inaugural atmospheric river and it could leave as many as three inches of rain on the Bay Area.

A typical year in the Golden State would see from 5 to 15 of these meteorological masterpieces, which tend to produce our biggest storms and floods. So as that first plume of moisture winds its waterlogged way here, you might want to learn more about what’s coming our way.

Back in January, meteorologist Brian Mejia with the National Weather Service in Monterey gave us a crash course in a weather pattern most laymen had never heard of before.

“Typically, you hear the term more on the West Coast because we get these low-pressure systems that transport moisture and water vapor,” Mejia told us. “And if they get deep enough they put out a plume, like plumes of clouds, and we’re now looking at just such a moisture plume being carried out by the storm system and into the heart of California.”

Want more? Check out these videos.

An Educated Take on the AR Phenomenon

A Sobering Look Back at the Damage Wrought by Rivers in the Sky

An AR in Living Color

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NOAA’s Michael Alexander Unpacks an Atmospheric River for the Rest of Us