There’s a kind of cold that’s legitimately dangerous. It can causes frostbite in minutes to unexposed skin. In parts of the Lower 48 states, such extreme cold is not uncommon, for a few days to at most a week.

But over the entire month of February and even into March, such exceptional, life-threatening cold never departed parts of Montana. Temperatures averaging 20 to 30 degrees below normal gripped huge areas in the state, as well as parts of the Dakotas.