There is significant year to year variability in terms of the Christmas weather in Finland, but in Lapland a white Christmas is almost guaranteed.

Probability of a white Christmas in Finland 

Statistical map of white christmas in Finland
Regional probability of a white Christmas. In Southwestern coast only every second Christmas is white. In Lapland a white Christmas prevails actually every year. The statistics are taken from the normal period of 1981-2010.

Global climate is expected to warm in the upcoming decades and so will the winter months turn milder in Finland. Therefore the above statistics will probably not be applicaple in future decades.

Christmas Eve temperature and snow depth

Weather on Christmas Eve beginning from 1981

Both temperatures and snow depths vary extensively from Christmas to Christmas. Here Helsinki is representing the weather conditions in Southern Finland, Jyväskylä in Central Finland and Sodankylä in Finnish Lapland.

The upper figure presents the daily maximum and daily minimum temperature in centigrades and the lower part shows the snow depth in centimeters.

Weather in Helsinki on Christmas Eve beginning from 1838

In the upper figure the red curve presents temperature in centigrades at 2 pm and in the lower figure the snow depth in cm.