With more snow on the ground in Southern Deschutes County be prepared for that when you visit the Fall River now. The difference in weather from day to day makes a huge difference in the fishing and even on how the fish will bite this time of year. I had a buddy there recently who fished 2 days in a row, one warmer and calmer and the second on a day the change to the pattern we are in was coming. The 1st day offered good hatches and plenty of catches on both dries and nymphs, that second day proved to be quite a challenge with much fewer fish even hooked, let alone landed.
There have been decent BWO hatches, some little black winter stones and midges all coming off and bringing the fish up to eat.
Nymphing euro style is likely your best bet in most places. That said, someone I know and trust said his party was going for a long drift with an un-beaded Pheasant Tail nymph, with really good success too. This is what I love about fishing, there are so many ways to approach the water.