A major storm system that brought heavy snow, coastal rain and high winds in the mountains of California is continuing a slow cross-country journey that is expected to last all week, forecasters said on Sunday.
The storm is expected to reach the Great Basin and the Desert Southwest by Monday, the Weather Service said, with those areas forecast to get up to two inches of snowfall an hour, which could make travel difficult.
By Tuesday, forecasters with the service said, the storm could develop into a major winter storm from the central High Plains to the Upper Midwest, which could result in “multiple days of significant impacts to travel and infrastructure due to snow, blowing snow and freezing rain.” The Weather Service emphasized that “travel may become impossible.”
In the Sierra Nevada, snow fell at a rapid rate of roughly three inches per hour over the weekend, blanketing roads and creating “nearly impossible travel” and “near-zero visibility,” the service said.
As of Sunday, the Sugar Bowl Resort, in the skiing areas of mountainous Norden, Calif., reported nearly four feet of snow, the service said. Other parts in the region saw about two to five feet of snow, which caused some highways near mountains to close.
In San Luis Obispo County, near the central coast of California, roadways were flooded and strong winds with gusts of more than 60 miles per hour brought down power lines, said David Gomberg, a meteorologist with the National Weather Service in Oxnard, Calif.
In Grover Beach, which is in San Luis Obispo County, all phone and 911 lines were temporarily down on Saturday night because of the winds. Service was restored early on Sunday, according to the city’s Police Department.
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Snow showers were expected to clear out for much of the Sierra Nevada by early Monday morning, said Hannah Chandler-Cooley, a meteorologist with the Weather Service in Sacramento.
Extreme winter hits the West over the weekend.
The storm system began to move ashore Friday evening, bringing strong winds to the California coast. But in the mountains, that moisture became heavy snow.
Forecasters had predicted “extreme impacts” — the gravest warning on the Weather Service’s winter storm severity scale — across the Sierra Nevada over the weekend.
The California Department of Transportation warned residents on Sunday to be wary of dangerous road conditions and closures in affected regions. Maintenance crews were still working to clear snow from lanes on Sunday afternoon.
As the low-pressure system moved ashore, it tapped into an atmospheric river — an area of moisture that flows through the sky like a river at a level of the atmosphere near where planes fly. The combination allowed for the snowfall total to reach one to three feet across much of the higher terrain.
Forecasters predict blizzard conditions across the Plains.
“We are increasingly confident that we will be dealing with a pretty significant Northern Plains blizzard” this week, said Greg Carbin, the chief of forecast operations for the Weather Prediction Center.
The system will move out of the Rockies and begin to strengthen, increasing the chance of heavy snow and very strong winds through Wednesday across the Northern Plains. The wintry blast is possible from Colorado, including Denver, and northeast across the Northern Plains. Across the Dakotas, at least a foot is likely, Mr. Carbin said.
“The potential does exist there for some really impressive amounts,” he added, as he expects this storm system will most likely slow down.
Severe storms, possibly with tornadoes, are expected across portions of the South.
It looks highly likely that severe storms, possibly capable of producing tornadoes, will form on Tuesday across an area from eastern Texas to Arkansas, Louisiana and much of Mississippi, said Bill Bunting, the chief of forecast operations at the Storm Prediction Center.
“Most fall and winter severe weather events typically have several features in common,” Mr. Bunting said, “including a low-pressure system near or north of the area of concern, a southerly flow of increasingly moist air from the Gulf of Mexico moving northward prior to the event and a cold front moving east towards the area.”
Tornadoes are not uncommon this time of year, but they are less likely than in the spring and early summer.
“We average about four days in December per year with at least one EF-1” — rated on a 0-to-5 scale of tornado damage — “or stronger tornado,” said Harold Brooks, a senior scientist with the National Severe Storms Laboratory, part of the National Oceanic and Atmospheric Administration. “There are about 100 days with an EF-1 or stronger tornado during the year.”
Severe winter storms like the ones predicted this week can be more dangerous than ones that form during peak severe weather season, in May and June.
“Because days are shorter,” Dr. Brooks explained, these storms are “more likely to occur after dark.” This “makes them more dangerous” because people in harm’s way cannot spot them as they approach, he said.
“They also are more likely to occur in the mid-South and Southeastern United States, which have greater rural population density than the Plains and have a higher fraction of manufactured housing and poverty,” he added. “Thus, the impacts can be greater.”
Snowfall in the Northeast.
Some snow fell across southern New England and upstate New York on Sunday. In Albany, N.Y., there were about five to seven inches of snow, said Bob Oravec, a meteorologist with the Weather Service.
About eight inches of snow fell in the Berkshires, Mr. Oravec added, and Hartford, Conn., recorded between four and six inches.
Boston and Providence, R.I., each had one or two inches of snow.
“Some areas may not have had much snow yet this winter,” Mr. Oravec said. “So any time you get snow, it’s always impactful.”
Christine Chung and April Rubin contributed reporting.