Hi Helen,

Dont be too worried, the sun wil still be out in Miami so it will always feel warmer to us than the Americans. As regards Vegas you seriously dont spend that much time outdoors because there is SOO much to do in doors!! And because they pump oxygen in the all the hotels you loose all track of time. I was there Last December and i only brought light clothes - Lets face it it's soo much cheaper to but a jacket over there than pay to carry it all on to the plane!!
Seriously dont panic it will be great & you will have a ball!!
Lisa