Snow began falling on much of East Idaho on Thursday afternoon, prompting the National Weather Service to escalate its winter storm watches to a winter storm warning and winter weather advisory that will remain in effect until 5 a.m. Saturday.

This is the most significant storm to hit East Idaho so far this winter season and is expected to make for difficult driving conditions even in lowland areas.

The winter storm warning that's been declared covers most of East Idaho's highlands, where maximum snowfall amounts of 6 to 18 inches are possible. The areas under the warning include Island Park, Ashton, Arbon, Tetonia, Victor, Driggs, Swan Valley, Palisades, Soda Springs, Bancroft, Grace, Thatcher, Inkom, Lava Hot Springs, McCammon, Arimo, Downey, Swan Lake, Georgetown, Paris, Malad, Preston, St. Charles, Montpelier, Bone, Henry, Wayan and Emigration Summit.

The region's higher mountains might see even more accumulation, with snowfall rates approaching an inch per hour at times, the weather service said.

The winter weather advisory calling for 2 to 6 inches of snow is for Idaho Falls, Ammon, Rexburg, Rigby and St. Anthony.

The rest of East Idaho, including Pocatello, Chubbuck, American Falls, Aberdeen, Blackfoot, Atomic City, Shelley, Firth, Rockland, Raft River, Idaho National Laboratory, Spencer, Declo, Burley, Rupert, Dubois, Craters of the Moon and Fort Hall, could see 1 to 3 inches of snow as well as rain during the storm.

Very gusty winds are expected to develop Friday afternoon through Friday night in East Idaho as the storm intensifies.

Road conditions are expected to be hazardous throughout the region due to the winter weather, especially in the highlands where road closures are possible.

The weather service advises motorists who must travel to keep an extra flashlight, food and water in their vehicles in case of an emergency.

Elsewhere in the state, winter weather advisories are in effect in the central Idaho mountains including Stanley, Ketchum, Sun Valley and Salmon while winter storm warnings have been declared in North Idaho.

Outside of Idaho, winter storm warnings and winter weather advisories are in effect in Montana, Wyoming and Utah because of the storm.