Yamaha 1300 Tourer - Yamaha 1300 Tourer Fansite

Wife and I, and our friends are riding to South Dakota July 28 to Aug 3, Deadwood/Sturgis area. I was wondering if anyone knows what kind of weather to expect around that time? If there's a fair chance of rain, then I'll take my full helmet, since it gets really miserable in the rain with the half helmet. I usually have a rain suit tucked in the saddle bags anyways.

I'm really looking forward to experiencing this beautiful part of the USA!

Thanks

~ kevin