I've had some of the best weather of all my trips in September. That being said a trip last year in the third week was one of the worst.

I don't approach an early or late trip much differently from a planning perspective with the possible exception of what sleeping bag I pack. What I do is take a look at the extended forecast just before the trip starts and maybe tweak a bit on the clothing (including footwear) and food that I pack. Not a really big deal, all things considered.

I heard that frost is predicted in some parts at least for tonight and maybe for a few more days down the road. So look at today as you would that day before entry - it will probably look worse. The weather this year has been atypical, and will probably continue to be so.

-aj