NOAA maps the probability of a white Christmas across the lower 48 states: the interactive version includes clickable locations.

While the map shows the historical probability that a snow depth of at least one inch will be observed on December 25, the actual conditions in any year may vary widely from these because the weather patterns present will determine the snow on the ground or snowfall on Christmas day. These probabilities are useful as a guide only to show where snow on the ground is more likely.

While the subject may seem whimsical, it’s based on 1981-2010 Climate Normals data; this paper details into the methodology involved. (It also answers a question that climatologists and meterologists get a lot.)