Deep cold and snow laying on christmas day is rare but snow actually falling on big day itself isnt that rare. Im at sea level and it snowed on xmas day 93 and 95 sure it did in 96 aswell also 99 and 2000 though cant remember it laying 2001 snowed just before christmas same in 2003, 2005 just after then 2009 and 2010 had laying snow and snow on day to then was an big gap till 2020 where we got brief flurry that left the thinnest covering.