A massive winter storm is sweeping the US, bringing up to two feet of snow and treacherous travel conditions for millions across the West. 

Storm warnings have been issued in California, Oregon, Nevada, Arizona, Colorado, Utah, North Dakota, Minnesota, Michigan, and Alaska, urging residents to stay off the roads due to possible whiteout conditions.

Blizzard alerts have been issued in Montana, South Dakota and Minnesota, where wind gusts of up to 60mph are expected to mix with several inches of snow, making travel unadvisable for anyone but emergency services.

In the Rockies and Southwest, several states are projected to see over a foot of accumulation through Friday.

Eastern California is expected to be the hardest hit, with the Sierra Nevada Mountains set to receive more than five feet of snow.

Parts of Oregon, Nevada, Arizona, Colorado, and Utah are predicted to see over ten inches, but totals could reach two to three feet at higher elevations throughout those states.

Bernie Rayno, AccuWeather chief on-air meteorologist, said: 'When this pattern finally wraps up late next week, parts of the Sierra Nevada will end up with 12 to 16 feet of snow.'

National Weather Service (NWS) officials have advised that anyone who must travel during this major storm should keep an extra flashlight, food, and water in their car in case of an emergency, an accident or if their vehicle becomes stranded.

Winter weather advisories have also been issued in Idaho, New Mexico, Wisconsin, Wyoming and Washington state.

Overall, up to 100 million Americans could be affected by this widespread winter event, with conditions ranging from ice and rain in the Midwest to extremely powerful winds combined with snow that could knock down trees and power lines in the Northern Plains.

Meteorologists expect most of the snow to fall on Wednesday, but conditions are expected to remain dangerous throughout the week.

Alyssa Glenny, AccuWeather meteorologist, added: 'Along with the obvious problems from heavy rates of snow will be the potential for avalanches through the passes and in the high country.'

At least nine skiers went missing after an avalanche trapped a large group near Lake Tahoe on Tuesday as this week's winter storm continued to rage out west.

On Wednesday, avalanche warnings were issued in California, Utah, and Colorado due to rapidly accumulating snow, weak snowpack layers and near-hurricane-force winds that cause drifting.

An avalanche is a rapid flow of snow down a hill or mountainside caused by an unstable mass of snow breaking away from the slope. Snow, rock, ice, soil, and other materials slide down during an avalanche and can reach speeds of up to 100mph.

In 90 percent of avalanche incidents, the snow slides are triggered by the victim or someone in the victim's party, according to NWS.

Outside of California, which is predicted to see the worst of the snowfall, parts of Nevada could see more than three feet of snow at higher elevations near the Sierra Nevada.

Northern Arizona is projected to receive up to ten inches of snow, but it will also be blown around by wind gusts of up to 65mph. 

An additional three to nine inches may fall on Thursday and Friday.

Colorado is projected to get between four inches and one foot. Whiteout conditions are likely, as winds could reach 70mph, just under the strength of a Category 1 hurricane.

North Dakota, Minnesota, and Michigan may see between three and 15 inches of snow through Thursday afternoon, with severe wind gusts between 35 and 55mph making travel on local roads dangerous.

NWS has advised anyone in the blizzard's path to stay indoors and travel only if absolutely necessary.

For those who have to travel outside, officials have urged Americans to dress in layers, cover all skin and watch for signs of hypothermia and frostbite, such as shivering, confusion, or numb skin.

For drivers, they recommend driving as slowly as possible during snow and letting someone else know your route before going out on the road.

Since blizzard conditions can trap motorists who cannot see what is ahead of them, it is important to stay in the vehicle if stranded and to run the engine periodically for heat while conserving fuel.