Winter storm could bring 10 feet of snow and rare white Christmas to parts of U.S.

A winter storm system could mean a rare white Christmas in parts of the U.S., with snow possibly piling up to 10 feet high in some areas.

The storm is expected to hit regions near sea level, including Oregon and Washington, according to the National Weather Service.

Meanwhile, snow could pile up as high as 10 feet in the central Sierra Nevadas.

Most residents in the Sierra Nevadas are expected to get 5 to 8 feet of snow. People are urged to avoid travel over the coming days because driving conditions could be hazardous.

“A series of Pacific storms will bring periods of heavy low elevation rain and heavy mountain snow to the Western U.S. through the Christmas weekend,” the National Weather Service tweeted Wednesday.

It also warned that flash floods and debris flows were possible near recently burned areas.

Cities like Portland, Oregon, and Seattle could have a rare white Christmas.

"More and more weather models suggest enough cold air and moisture will overlap across the region to produce accumulating snow to near or at the valley floor beginning Saturday night and continuing into Monday," the National Weather Service in Portland tweeted Wednesday night.

The weather service said "additional rounds of snow are probable next week," as well.

In a separate tweet, the National Weather Service in Seattle said "widespread heavy snow is NOT expected through Christmas Day." However, it said, some snow is possible.

The weather service said that if Seattle does get snow, it would most likely be Saturday evening through Sunday night.

"Much of the lowlands could see 3-5" of snow in the most likely scenario," it said.

The weather service said Seattle has recorded "measurable" snow on Christmas Day just seven times in 127 years. The most, 1.8 inches, was in 1909.

For much of the U.S., a white Christmas appears unlikely.

Just 26 percent of the country, excluding Alaska, was covered by snow Thursday, according to data from the National Oceanic and Atmospheric Administration.

The technical definition of a white Christmas is 1 inch or more of snow on the ground on Christmas Day, according to the National Weather Service.