I haven't really kept track of it. The desert southwest, of course, has periodically experienced incredibly high temperatures, even by their standards. I was looking, however, at that Glacier message board and there were comments to the effect that unseasonably warm temperatures and drying weather would soon lead to elevated fire hazards. I haven't specifically heard of any fires yet in the greater Glacier ecosystem. A lot of squirrely things can still happen between now and your departure, for better or worse, that could impact the quality of fall foliage. One year that we went to Glacier, I remember park personnel informing us that they had gone through a series of cycles of unusually cold overnight temperatures, followed by much warmer periods, all of which preceded the onset of the traditional fall season, that collectively, "confused" aspen, to the point that many of their leaves browned before turning to their traditional gold. There was still fall color worth seeing, but the damage had already been done.
In short, no two years are the same in terms of predicting the quality or timing of fall foliage.
Incidentally, there appears to be one sparsely visited message board on Trip Advisor (
https://www.tripadvisor.com/ShowForum-g143029-i1019-Grand_Teton_National_Park_Wyoming.html) pertaining to the Tetons); you might check on it periodically and/or GTNP's website to chart unusual weather patterns and/or fire hazards in the area.
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