Hey Jim,

I will be doing Yellowstone in Late September. The fires in Yellowstone are rather small compared to the ones that have been around Glacier....on the order of 1/20th the size. Also, Yellowstone's fires are in the SE section - mostly in the back country, so it will have little affect on most people's trip experience.

Late Sept is the best time - IMO, to visit Yellowstone (though it is always great to me). The Aspens start turning bright orange around this time. The rut is also at its peak for Elk. A little later, the moose start going through it. Wildlife is abundant, and there are fewer people in the park - making it an even more wonderful experience.

Cheers
James