. Our family goes to Disney World every August and I spend a lot more time outside at Disney, so the heat is more of an issue (and not a huge one IMHO). I do enjoy walking on the Strip in the early morning in Vegas, before it gets too hot.
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To compare, put your oven on 450, let it heat, stick your head in. That's what it's going to feel like in Las Vegas in August.
It's flippin hot and that's from someone who's lived here their entire life. I don't even take my kids outside in the summer. The up side of that is it's January and 54 degrees out right now. We wear shorts well into October. If you have the choice do April/May instead.