Sorry for this generic answer but it is the truth.
When the snow gets deep enough to cover their feed up high to where they can''t get to it. It might start in October or December, it just depends on the year. I know of a herd in Utah that winters at 9500' + just because the wind blows the snow off of the high ridge that they live on and there is feed all winter long.
Like this last winter for example. Where I live here the winter was so mild I never saw any elk come down as usual. In general there are several hundred not far from the house by December/January but they never made it all this year.
All of us, at one time or another have gone on a hunting trip and had what we call “Blue Bird” weather. Warm evenings and almost hot days. We hunt in our t-shirts and enjoy the sunshine. We are way up in the mountains and have a whole week to hunt. How could it get any better?
That is, until we score on that big buck or bull. We work to get it out of the field and skinned as quickly as possible to cool it down. But try as we might, we just can’t get...