‘Atmospheric River’ is set to bring heavy rain and snow to US Northwest

A potent weather system known as an atmospheric river is poised to bring heavy rain and snow to the Pacific Northwest and California, raising the risk of mudslides and floods.

The series of storms developing over the Pacific Ocean could dump as much as 7 inches (18 centimetres) of rain in Northern California in the next several days, US Weather Prediction Center meteorologist Josh Weiss said in an interview. The Sierra Nevada Mountains may receive 4 to 5 feet (1.2 to 1.5 meters) of snow. 

Atmospheric rivers are powerful streams of moisture that flow off the Pacific, in some cases carrying as much water through the air as the Mississippi River holds in its mouth. 

While the heavy rain could trigger flooding and mudslides, it’s also crucial for a region that’s in the midst of its worst drought in 1,000 years. California depends heavily on winter rains to replenish its reservoirs. As of December 20, 97% of the Golden State was in some level of drought.

After soaking the West Coast, the storms are expected to form a low-pressure system that could deliver heavy snow to the Great Plains next week and, eventually, bring rain to the East Coast, Weiss said.

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