People who have been dreaming of a White Christmas or singing about weather outside that’s frightful will be getting their wishes this holiday weekend.

A potent storm is heading toward much of the western and central United States Saturday and Sunday.

The system is forecast to bring everything from a wintry mix and a blizzard to drenching rain and severe thunderstorms to a large swath of the U.S. from Friday through Sunday. Only the eastern part of the country will remain relatively tranquil.

The storm first moved into the West Coast on Friday, bringing heavy rain and the potential for flash flooding in California, with heavy snowfall expected in the higher terrain of the Sierras, the National Weather Service said. Snow will also fall over the Cascades, northern Great Basin and northern Rockies.

The heaviest precipitation was expected to fall through Southern California, the weather service forecast.

As the system pushes eastward on Saturday – Christmas Eve – conditions should begin to dry out by the weekend along the West Coast, the weather service predicts.

By then, the Rockies will see additional snow, which will spread into the Plains by Saturday evening. On Christmas Day, howling winds of up to 60 mph and heavy snow totaling up to 9 inches will likely lead to a full-fledged blizzard in portions of the Rockies and the Dakotas.

Travel may become “impossible” in those areas Christmas Day, lingering into early Monday, with numerous roads, including major interstates, likely to be shut down, the Weather Channel said.

On Friday night, more than 3,000 flights in the United States were experiencing delays, according to the Flight Aware website.

“This has the potential to become a widespread and significant winter storm across the northern Plains,” the National Weather Service in Bismarck, N.D., warned.

In Phoenix, the National Weather Service issued a winter weather advisory for snow and blowing snow that will be in effect from 5 p.m. local time Saturday to 5 a.m. on Christmas day. The National Weather Service estimated up to 12 inches of snow for Flagstaff, Ariz., and other areas and up to 4 inches in Prescott and Payson, Ariz.

The Weather Channel has named the storm Winter Storm Europa.

Farther east, in the Midwest, milder air will mean rain and wet travel conditions for cities such as Chicago, Detroit, Indianapolis, Des Moines, Iowa and Omaha, Neb., on Christmas Day.

To the south, in the central and southern Plains, thunderstorms will “bring the potential for large hail and isolated tornadoes” on Christmas afternoon, AccuWeather meteorologist Brett Rossio said.

A few isolated, severe thunderstorms are also possible in southern and eastern Texas into Louisiana by Monday.

Other than some scattered showers Friday and Saturday, most of the eastern U.S. will enjoy a calm, mild holiday weekend, though some wintry weather is possible in northern New England by Monday.

Contributing: Arizona Republic