(Reuters) – Heavy rain and snowfall hit parts of California, Nevada and Oregon early on Wednesday, causing roads to be closed, schools to cancel classes and widespread flooding along already swollen waterways.

A National Weather Service blizzard warning remained in effect until late on Wednesday morning for ski resort towns in the greater Lake Tahoe area, including 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 National Weather Service reported.

An avalanche warning was issued for much of the same mountain regions.

“Those venturing outdoors may become lost or disoriented so persons in the warning area are advised to stay indoors,” the weather service said.

Roadways, including Interstate 80 near the border of California and Nevada, were closed on Wednesday morning.

Schools throughout the region canceled Wednesday classes, including the Portland Public Schools district in Oregon, attended by about 50,000 students.

Several flood warnings remained in effect until Wednesday morning for lower elevations in northern and central California and in western Nevada, where creeks and rivers were expected to overrun their banks.

Several communities in the region opened evacuation centers for people who heeded warnings from officials to move to higher ground to avoid flooding.

Heavy downpours sent a wall of mud down onto a house in Fairfax, California, trapping an elderly couple and their two granddaughters, according to local media. Firefighters rescued the couple and children and no one was injured, an ABC affiliate reported.

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.

The 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.

(Reporting by Brendan O’Brien in Milwaukee; editing by Dominic Evans)