Rain and snow are forecast to pummel California this weekend, all part of a 10-day storm cycle that could bring inches of rain and upwards of 20 feet of snow to some mountain regions. This follows a tumultuous week of weather—especially in Lake Tahoe—where 4 to 7 feet of snow has already fallen and some roadways are flooded.
Skiers and snowboarders hungry for powder are calling California’s 10-day forecast the “most insane forecast ever.” That’s because precipitation totals in the Sierra are forecast to be approximately twice the monthly average for January. But all that moisture has a downside too, with some forecasters predicting that California will see the worst flooding since 1997.
The Science: Atmospheric River:
All of this precipitation is caused by an atmospheric river (AR), a narrow band of moisture that can transport huge amounts of water vapor towards the West Coast. Think of an atmospheric river as a fire hose that funnels moisture from the tropical Pacific towards California.
Thanks to a blocking high pressure system near the Bering Sea and a downstream plunge of the jet stream off the Pacific Northwest Coast, the atmospheric river is set to stall over California for at least two or three days starting on Saturday.
When an atmospheric river stalls over land, you can expect big precipitation totals.
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