This year's OW Winter Event is from December 10th to January 2nd.
3 separate week's worth of skins and sprays to get again.
This time round it seems to have a slight variation of the snowball fight mode from last few years. Snowball Deathmatch will be a separate gamemode to choose in the Arcade mode.
Also, noticed that Mei catches a snowball thrown at her - I'm not sure if that's just her ability or a common one for everyone which should be what's happening.
I must admit although it's not really different to the last few years, I've always found the snowball fights to be some really good lolz with everyone. Could even be a great FG party night between us all the OSK (One Snowball Kill) about.