We've been talking about the weather all week in the run up to tonight's 2011 Winter Classic, and since this game is played out in the elements and not in the controlled confines of an indoor arena, there are little alterations that have to be made to the typical rules governing play.
One of those changes: at the 10 minute mark of the third period, the play will be whistled dead as if the period ends with what the NHL calls a "hard whistle." The teams will switch ends for the remainder of the period, and the ensuing face off will take place at the spot play was whistled dead.
If the game goes to overtime, the same thing will happen at the 2:30 mark.
As rain falls on Heinz Field in this third period, it's worth noting that the game is now considered "official." Much like playing beyond the fifth inning of a baseball game, if the weather forces this game to stop, it won't be replayed or finished.