Late August through Early October is autumn around here. This weekend, still before Oct. 15th, we're moving right into winter, with snow accumulation predicted. Nearby Yellowstone and Grand Teton National Parks will get 6-16 inches, depending on elevation!! Halloween is often white, with temperatures close to 0 degrees Fahrenheit. However, deep winter is actually warmer than places like Northern New York and of course the Upper Mid-West.