Dress warm.
Cold spell coming to the western US. Highs in Vegas in coming week to only be in the 40s, with lows below freezing.
Weak storm possibly moving in December 31, snow possible as 2015 arrives in Vegas.
Would not advise standing outside for NYE for hours in Vegas unless you are used to cold weather.
Times Square is only going to be a few degrees cooler, and with no snow.