Check NPS site for google avg temps at Phantom
Buckman...that data is mostly for locations at 6000'+ or 7000'+ elevation. The Waheap data is more applicable, as it is on Lake Powell at about 3700' elevation. Lee's Ferry sits at 3210'. When I first looked at that link, I was a bit nervous for my Feb 2016 trip. The daily lows in Feb for the first two locations listed were in the 20's and high in the 30's and 40's. But, then I noticed that the elevation for the weather readings were 6500' and 7200', a big difference from river level in the canyon. The Waheap readings had highs in the 50's and lows in the 30's. I would expect canyon (mostly in the shade) temps to be around the Waheap readings. The precip data is helpful, though.