With strong winds in place, any snow that falls will likely lead to possible blizzard conditions.
"Suffice to say: this will be a historic storm".
"This early season winter storm and/or blizzard has the potential to set a new benchmark for snow accumulations, cold temperatures, and resulting impacts for parts of the Northern Rockies and the Rocky Mountain Front".
The NWS warned that travel would be "hazardous" due to snow and there is the potential of "life-threatening" backcountry conditions.
Cold temperatures and wind chills are also expected Sunday in the Northern Rockies and the Pacific Northwest. "Extreme impacts are possible with this storm, including to the power infrastructure (downed power lines resulting in widespread power outages), agricultural interests, outdoor recreation (camping and hunting activities), and travel". Its website advises that residents should have water and food available that does not require electricity to prepare, have batteries for a flashlight and a radio on-hand in the event of a power outage and consider moving vehicles away from power lines, which could become unsafe if snow were to accumulate on them.
They said residents should stock up on food, move vehicles away from trees and power poles and prepare flashlights with fresh batteries.
The NWS said in a report: "This is a significant fall storm that could produce significant widespread impacts". That includes larger population areas like Helena, Butte, Great Falls, and Havre in Montana.
And to make matters even worse, more snow is expected next week. These bitterly cold conditions are expected to last for days after the storm. It will be followed by another low-pressure system that will stall over the region Friday night through Sunday.
That will be followed by temperatures plunging to unseasonably cold levels early next week, with the coldest spots dropping to the teens and 20s.
The NWS said that the region has not seen a storm of this magnitude since 1934. Highs will be in the 40s and 50s.
They say any fire that develops will likely spread rapidly.