Cold, cold, cold. A wet or drysuit will be necessary in the water. Be prepared for snow, which by my standards makes quite lovely photographs. No need to worry much about upsteam thunderstorms flooding the canyons. Light will be less directly overhead and so may mot reach the bottoms, where you will likely be. None of the deciduous trees will be leafed out (mid-April). But I'm with ya. No pain, no gain.