At Louisville, the last Christmas with snowfall (a trace) was 2005. Last Christmas with measurable snowfall (0.5") was 2002. Last Christmas with snow on the ground at 7am was 2004 (8"). Most snow on Christmas ever was 5" in 1890.
Notice on the map below how history is not on our side in hopes of a white Christmas. The probability of a white Christmas for Louisville is 13%. The chances go up the farther north and east you go. South of the river chances drop to around 5-10%, but go up to 10-25% in southern Indiana.
I'll go ahead and say our chances this year are more than 90% for a white Christmas. The models are getting more consistent in bringing accumulating snow Christmas Eve. 2-4" likely for much of the area by midnight Christmas Eve!