I'll be in Rome for Christmas and Venice for New Year. Though the weather anywhere is "as changeable as the weather"...any recent experiences with Italian weather in December? Thanks!
I will also be in Rome and Venice during that time and from what my travel partner has prepared me for (since he has been every year during December for the past few years) is COLD COLD COLD! (although you are from NYC...and I'm from Australia...you might cope better!). I've had to go out and buy thermals, polartec clothing and plenty of scarves because it does apparently get incredibly cold, something like no more than a few degrees C.
Apparently Venice is likely to be very misty and probaly the coldest place we are going while away, but as you've said can't always predict the weather.
This site gives you 15 years of actual weather for your location and travel dates: http://www.wunderground.com/tripplanner/index.asp