As is typical of desert locations, there’s generally a marked contrast between daytime and nighttime temperatures in Las Vegas at this time of year and the less cloud cover there is, the chillier the evenings will be. While the weather is fairly consistent from year to year, it's not 100% predictable. For example, we had a cold spell earlier in December, but in the days running up to Christmas people were out shopping in shorts and T-shirts.
We logged on to the National Weather Service Forecast Office site for Las Vegas and the seven-day forecast commencing December 29th was predicting daytime highs from 56 to 62 degrees and nighttime lows in the 38- to 44-degree range. For an update, you can check it again right before you leave by clicking here.
As far as temperature levels indoors are concerned, casinos are notorious for keeping them pretty low. In the summer months, when outside temperatures soar well above 100 degrees, the 40- or 50-degree discrepancy when you step inside can be hard to adjust to and it's not uncommon to catch a cold or a chill here in the summer months, even if it's 115 degrees outside. But in the winter, you’ll find that indoor and outdoor temperatures are closer and that it's often warmer inside than out. We phoned around a few casinos to find out what standard temperature they maintain and discovered that some are significantly warmer than others: MGM Grand - 65 degrees; Paris - 68 degrees; Excalibur -70-71 degrees; Golden Nugget - 74 degrees; Gold Coast - 68 degrees.
As far as wardrobe considerations go, you might get lucky and find yourself in T-shirt weather, but definitely pack some sweaters, long pants and jackets, and you should be covered for every eventuality.
