Snow is guaranteed in Lapland from December to the end of April. From December through February, the temperatures do get pretty cold—-25 centigrade (-13 Fahrenheit). But because the air is so dry, even that cold weather is acceptable and you won't be shivering from the cold. As long as you have good warm insulted clothing, you can do just about everything you want outside.
The days are longer than in western Europe from the middle of February on. These long days lend themselves to long days on the snow for cross-country skiing.