(NewsNation) — A strengthening storm system will bring heavy mountain snow and coastal rain to the West Coast this weekend.

The storm over the Pacific, according to AccuWeather, will set the stage for severe weather and blizzard conditions in the nation’s midsection in the coming week.

“An impressive stream of moisture from the Pacific associated with an atmospheric river will help to promote both high rainfall and snowfall rates as well as totals,” the National Weather Service said.

The northern Sierra Nevada is forecast to get as much as 4 feet of snow in the upper elevations around Lake Tahoe. A winter storm warning was issued for a 250-mile stretch of the Sierra beginning late Friday north of Reno along the California-Nevada line. At 4 a.m. Saturday, the storm warning went into effect around Lake Tahoe and as far south as Mammoth Lakes. These warnings don’t expire in most areas until Monday.

The U.S. Forest Service activated a backcountry avalanche watch late Friday in the central Sierra including Tahoe. It warned of higher avalanche danger going from Saturday into Sunday.

“A winter storm with gale force winds, high-intensity snowfall and feet of new snow accumulation may result in widespread avalanche activity in the mountains,” the Forest Service Sierra Avalanche Center said Friday.

Although the rain and snow will stop, its effects will still be felt in the form of a “cold airmass,” AccuWeather said.

Travel over Insterstate 80 might be “nearly impossible” to navigate, AccuWeather said, and snow-packed and slippery roads could make roads hazardous.

There are some benefits to the large amount of snow piling up in the mountains, though. AccuWeather says a greater snowpack means more snow that will melt away in spring and summer, which can help boost soil conditions and water levels.

In Southern California, NewsNation local affiliate KTLA reported, forecasters are expecting 1 to 2 inches of rain in the coats and valleys, while local mountains and foothills are expected to get up to 6 inches.

There’s a potential for flash flooding, and winds could reach 20 to 40 mph. On Sunday morning, Los Angeles will see its heaviest rain from 4 a.m. to 10 a.m.