I'm an avid bass guy but don't bother much with them in winter.
They're catchable under certain conditions (had a big SMB chase a muskie streamer a couple weeks ago on a river with iced over tribs) but its especially tough with a fly rod. Ice fishermen on lakes catch 'em from time to time. Generally speaking, winter SMBs are in the deepest, slowest, sections of medium to large rivers. They'll lay inactive on the bottom for weeks at a time. If water temps rise for a few days they will eat. The magic number, in my experience, for river SMBs is 42 degrees. My guess would be, with the recent snow melt, that most rivers are lower than that. If you know of a slow, deep, shoreline eddy where you can fly cast, it's worth a try. Wait for a sunny afternoon and fish a streamer low and slow. You might have a pleasant surprise.
