The map above is the current snow cover (as of 13 December 2013) in the US according to the weather.com. Compare this to National Oceanic and Atmospheric Administration map from the last few years of Christmas morning snow cover over the last five years.
Combining such maps from 1908 to 2010, NOAA maps out the probability of a white Christmas (that is, 1" of snow on the ground).
They also have a report from 1995 that maps the probability of 1", 5", or 10" of snow on Christmas morning.
Except for the Northeast, a many of the areas of the greatest chances are not densely populated.
I wonder, what is the expected percentage of the US population that experiences a white Christmas?