The Box has been fishing constantly all winter. The issue you will have this time of the year is access. Getting a boat in or more importantly out is going to be a challenge! I have seen a couple of guys floating it in a raft. If you have access to a snow machine getting down to the water will be a piece of cake and once your in it’s easy from there. I would have the usual. Small beads and rubber legs. This also a great time of the year to slow swing streamers. I would have Matukas in both olive and brown.
Once again access with a boat will be your only challenge. On the right day the fishing on the lower river has been good. I have seen fish up eating midges on the surface and nymphing has been very good. Have some #18 Griffith Gnats and the usual bead heads with you. I like brown or red zebra midges with a #10 black rubber legs. Swing streamers in the long runs that are found on the lower Henry’s Fork. It has been very cold this last week but hopefully things will start to warm up a bit with the next round of snow storms.
Once again…you guessed it, access is the main issue on the South Fork. I do like this time of year on the South Fork because wading becomes a little easier. I would have all the patterns I have suggested above and if you can get on the water when the temps get above freezing, you just might have a great day without the crowds.