(Reuters) - An atmospheric river of moisture swept parts of California and Nevada on Tuesday with another bout of heavy rains and snow, swelling streams to flood stage and piling up wind-blown snow drifts several feet high in the mountains.
The National Weather Service issued a blizzard warning for ski resort communities in the greater Lake Tahoe area, including the towns of Truckee and South Lake Tahoe, California, and neighboring Nevada enclaves of Stateline and Incline Village.
Snow accumulations of 5 to 10 feet (1.5 to 3 meters) were forecast above elevations of 7,000 feet, with fierce wind gusts reaching 100 miles (160 km) per hour along the ridge of the Sierra Nevada mountain range, the Weather Service reported.
"This is a life-threatening situation," the weather agency said in a bulletin issued from its office in Reno, Nevada, urging all would-be travelers to stay indoors. "Even a short walk could be deadly if you become disoriented."
The blizzard warning was set to remain in effect through Wednesday morning. An avalanche warning was issued for much of the same mountain regions.
Schools throughout the region were closed for Wednesday, including the Portland Public Schools district, attended by about 50,000 students.
Flood warnings were posted at lower elevations for 21 counties in northern and central California and a half-dozen counties in western Nevada, where creeks and rivers were expected to overrun their banks for a second straight day.
A series of floodgates on the Sacramento River, just upstream of California's capital, were opened for the first time in 11 years on Tuesday to divert high water around the city and into a special drainage channel, said Lauren Hersh, a spokeswoman for the state Water Resources Department.
Heavy downpours on Sunday night and early Monday forced some 3,000 people to flee to higher ground in California's Russian River valley, while about 400 homes were evacuated in Reno as the Truckee River topped its banks there.
Tuesday's cascade of rain and snow marked the fourth round of extreme precipitation unleashed during the past month by a weather pattern meteorologists call an "atmospheric river" - a dense plume of moisture flowing from the tropical Pacific into California.
The storms have brought some sorely needed replenishment to many reservoirs left low by five years of drought, while restoring California's mountain snowpack to 135 percent of its average water-content level for this time of year as of Tuesday, state water officials said.
"The wet start of winter makes us cautiously optimistic that drought conditions will be alleviated" in parts of the state, though some areas have remained dry, Water Resources Department spokesman Ted Thomas said.
Reporting by Brendan O'Brien in Milwaukee; Editing by Bill Rigby and Himani Sarkar