Madison River 1670 CFS below Ennis Dam, 1270 CFS near Cameron
The Lower Madison continues to fish well despite the changing weather. The Lower is still a bit colored, but plenty clear for fishing. Sculpins and crayfish (as usual) with various droppers: still some caddis pupa even with the cold weather, break out the baetis nymphs/emergers again, and some attractor nymphs. Look for good streamer fishing with the clouds and strip slowly (behind the boat), or throw dries, they will be rising in the flat water. The Upper has been pretty good as of late with streamer fishing and nymphing producing more than dry fly fishing. March Browns are around and there should be some BWO's as well.
Missouri River 3780 CFS below Holter Dam
Nymphing has been quite productive on the Mo, and the dry fly guys are having food luck with March Brown patterns as well. Springtime on the Missouri River can be quite good if the wind is not howling (which it can), and the fish are eating (which they are). Fish however you like, you will catch them here.
Jefferson River 2510 CFS at Twin Bridges
As I thought, the Jeff is dropping hard with the cold weather, and if you know the river well, you will probably catch some great fish on the drop. The water is pretty cold, so streamers should move slowly, but nymphing will be quite good. Look for March Browns here in great numbers, throughout the river.
Gallatin River 1400 CFS near Gallatin Gateway
The Gallatin River is dropping as well, and the clarity has really improved. Nymphing has been quite good: stonefly nymphs and San Juan worms are all you need here right now, do not make it too complicated.
Yellowstone River 6440 CFS near Corwin Springs
If you are comfortable gambling a bit with your fishing day, head to the Yellowstone River. It too is dropping quickly, and it is possible to sneak in for a brief lapse in the spring runoff for some outstanding fishing. Or, you may get your teeth kicked in... Streamers and large nymphs close to the bank.