On December 13, which probably means the December 14 for us down here in Futureworld. The announcement came via a tweet with an animated GIF inviting players to an Overwatch holiday event, showcasing a snowy version of the King's Row map. As to what the timed-event will include is anyone's guess, but if we were to go by the seasonal events we've seen so far you can probably expect Christmas-themed skins, emotes, and perhaps a new game mode.