We are travelling to Vegas for the first time in September and was wondering if anyone could tell me what the weather is like then? We'll be there from 14th-21st. How hot will it be? What kind of clothing will we need to take? Will we be able to spend our days lounging by the pool? Also, we plan on visiting the Grand Canyon while we are there. How hot will it be down in the canyon? Will the heat be too unbearable at this time of year?