With extreme cold temperatures look for the fly fishing on teh river to slow a bit. The fish will move to slow moving water and deeper pools. The river usually fishes well all winter you just have to pick your spots. When we have cold weather the best times to fish are early afternoon when the sun has had a chance to warm the water a degree or two. The best days are when we get a day with air temperatures the rise the most. A day in the 50's after a few days in the 40's is always best. Down size your flies and make sure you are getting a good dead drift in slower water. The fish will not chase flies to far this time of year so work the water slowly and cover every inch of a good run.