Just days before Punxsutawney Phil is scheduled to emerge from his groundhog home in Pennsylvania and predict the duration of winter, human forecasters say California will get pummeled by rain and up to three feet of snow this weekend, thanks to an atmospheric river.
For Southern California, the heaviest rains are expected to fall on Sunday and could trigger mud and debris flows near recent burn areas, as well as widespread pooling of water on roadways, according to the National Weather Service.
Forecasters say a damp band of air originating in the tropical Pacific Ocean is headed for California. Once it arrives, this river of vapor will slam into Northern California's towering Sierra Nevada, "just dumping and dumping so much moisture," said meteorologist Alex Hoon, of the National Weather Service in Reno.
"We have a pretty healthy looking winter storm coming in the Sierra," he said.
In Southern California, the fast-moving storm will bring three to six hours of moderate to heavy rain on Sunday, as well as high surf, mountain snow and gusty winds.
Heavy snows are possible above 6,000 feet, and snow elevations will drop quickly late Sunday, possibly affecting traffic along Interstate 5 near the Grapevine that evening or early Monday.
At the beaches, surf could reach 20 feet along the central coast and 14 feet near Ventura Harbor. The high surf will likely cause beach erosion with dangerous breaking waves at Morro Bay and Ventura Harbor entrances.
This weekend's storm has a number of unpredictable qualities, say forecasters. If it lingers longer than a day over a region it could cause flooding throughout California, Hoon said.
In the Sierra, snow flurries could begin blanketing high elevations by Friday, with snowfall likely increasing through the weekend. Forecasters say the Sierra will likely see 1 to 2 feet of snow on mountains above 8,000 feet. Up to 3 feet of snow is expected to cover the communities north of Mammoth Mountain and south of Lake Tahoe.
Forecasters warned that the threat of an avalanche will be considerable Friday, because of the combination of wet snow and wind on higher mountain elevations. The falling snow is "classic Sierra concrete," meaning it will be heavy wet snow, Hoon said.
The storm should be more good news for California's snowpack, which this month reached its highest level in five years.
"This storm is going to add to that," Hoon said. But Hoon warned that one season of rain is not enough to get California out of drought.
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