If for camping, you probably do not need to consider the weather on the passes, because you're not likely to camp on the passes. Anyway, I plan my clothing and camping choices to be the least that will keep me alive in the worst possible conditions. It's okay to be uncomfortable in unusual weather--you just don't want to die. I plan my clothing such that on the coldest night, I will be wearing everything I brought at the same time.^ This except, I want a little better than not dying, I want to be sure of keeping all my fingers and toes
For the TA at that time of year, I'd expect frost at some point and to be over 100F at some point. We did it an exceptionally hot year and 100F a lot of the way, but even on that trip we had some moderately cold nights (never much below 32 F). One evening it was bitter cold and a howling wind on top of a pass, but we rode down into the next town and it was much warmer where we camped.