I think the official title actually is 'Three State, Three Mountain Challenge'. I've never done it but I've heard good things about it. I had it in my list of possibilities for this year but I just found out that a good friend's wedding is that day so I guess I'll have to aim for next year instead.

As far as weather goes, unless it rains, it will be pretty warm. I'm guessing a daytime high for that time of the year will be in the 80's. But, when you start in the morning, it will probably still be a little cool. Also, it's cooler in the mountains and the decents can be kind of chilly. I would recommend dressing in layers so you can add/subtract as needed throughout the day.

Have fun with this! It's a great ride and you will love the scenery!