I am pretty sure he remembered accurately; 60 and 80 degree temperature swings are real common here where I live.
Mostly in September and October, but sometimes in March and April.
Haven’t had a 100 degree swing yet, but I am just waiting for it to happen.
I am somewhat further south than Montana, but I am sure it could happen.
I’m sure the substance is accurate, but details can sometimes grow for effect.
I have an ancestor on that side that was nearly hung as a spy (in Missouri) during the recent unpleasantness between the states, but told those about to hang him that they would have the welfare of his 10 kids on their consciences...while most of the details of the story have become remarkably consistent, what side he was spying for has varied.
Another good story from that side has to do with a feud that ended with part of the family migrating from Missouri to Oregon (though not the part that I’m descended from). Whether the feud was over a woman or a pig is a point of contention, though, to quote one of my great uncles, knowing our family, it almost certainly was the pig.