Winter has seemingly set in early across Montana with widespread snow on the ground and cold temperatures. The current setup can be a vicious cycle as snowpack tends to lock in the cold, even making it colder and colder.
Snow is cold, and it has to be cold to snow. Snow on the ground can make the air temperature above it get colder and colder, and that same ground snow tends to lock in cold air. During the day, snow reflects the sun's radiation minimizing warming. Because snow is highly reflective, a vast amount of sunlight that hits the snow is returned back into space instead of warming the planet. Without snow cover, the ground absorbs about four to six times more of the sun's energy. High temperatures are usually lower than what they would be without snow on the ground.
At night, snow helps with radiational cooling making temperatures colder. Limited energy or radiation absorbed during the day radiates back out to space at night. Snow on the ground enhances this process making overnight temperatures colder.
If there happens to be some sunshine that creates melting or sublimation of snow, these are cooling processes due to conservation of energy in the atmosphere. These changes of the physical state of the snow further limit warming at the surface.
The days are colder, the nights get colder, the next day starts out even colder and so on and so on. If there is a large area like the size of Montana covered with snow, the entire airmass cools making it harder to warm when a warmer airmass or new storm moves into the area.