The Gallatin River is a great winter fishery. With mild winter weather there are very few ice shelves and the entire river is a great option. Nymphing is the way to go and make sure to focus your efforts in the big, slow runs where fish stack up in the cold season. Smaller mayfly style nymphs and midge larva are your best bet but egg patterns can still produce as well. Takes are subtle and try some more sensitive indicators like yarn for best results.
The Month Ahead:
The Gallatin should remain productive all winter as long as you focus on late morning and afternoon fishing. When cold snaps hit ice slush and ice shelves can be an issue. There are some springs that come in mid river near Big Sky and that area is more ice free than others during a cold snap. As you go down the valley expect more ice on the really cold days.