The Lochsa can come up in the winter, but it's pretty rare. And it comes and goes quickly. We had about 4 days of boatable water last Jan, maybe a bit more. It was up to 4' for about two days. What a hoot. Yes, it was raining and we just beat a major ice floe coming down the river. Ice is a significant factor esp if the banks are frozen or the ice is bridging.
The Alberton gorge is boatable year round as long as it is not frozen over. So is Beartrap, and I think that rarely freezes over.
I am a river, babe - I've got plenty of time, I don't know where I'm going, I'm just following the lines..... - "We are water" by Shaye