The snowstorm will arrive in the Canadian Rockies late on Monday and push into the northern Rockies of the United States throughout Tuesday, but it will not stop there.

The National Weather Service has posted winter storm watches for parts of the Northern Plains states, with more warnings and advisories expected in the days ahead as the winter weather sweeps much further south.

By Wednesday, any rain over the Northern Plains and High Plains will turn to wet snow from parts of Montana into Wyoming and the western Dakotas.

Cold air plunging in with the storm will allow snow to accumulate and travel conditions to deteriorate, not only in the highest elevations but also in the valleys.

The heaviest snow is expected over higher ground in Montana, Wyoming and Colorado, with at least 15 centimetres (six inches) also possible in the central and western Dakotas.

Denver and Cheyenne in Wyoming will both see their first snow of the season and it could well be several centimetres.

Temperatures will plummet as the cold air and snow arrive, with Billings in Montana going from a high of approximately 21 degrees Celsius (69.8 degrees Fahrenheit) on Tuesday to below freezing as the snow falls during the night.

With leaves still on the trees, and some very strong, gusty winds, we could well see tree damage and more significantly, widespread power outages.