Hi Claire, I went on the National Parks tour in October 2011,it is a fantastic tour. The Wyoming tourism office thought it may be affected by snow, but, although it did snow going towards Yellowstone, it wasn’t bad enough to stop us going into the Park. It was cold in South Dakota, although the morning at Little Big Horn was warm and sunny. The further south we went, the warmer it got.
I am on the October 3rd Canada and New England in the Fall tour and staying on in Boston, I have been there several times before, so looking at some day trips outside the city.
Keith