Looking at this NOAA National Weather Service
report for Phantom Ranch may be useful.
I see rain and highs in the 40's coming up in the next week at Phantom Ranch -- not atypical for the dead of winter down there. Yeah, it says "sunny"for a few of those days, but in the depths of the gorge, fat chance you're going to enjoy that for long. Then I think about running Horn, Granite, Hermit, and Crystal in that next stretch of river -- without a dry suit -- and I ponder how much fun that's going to be for passengers. Heck, from where I sit (concededly at age 65 and greatly diminished in metabolic resilience) I don't think it would be fun for the boatman either.
Reconsider my friend, if they don't seriously tighten up their game.