It's going to be 28 and drizzling which will freeze on your boat. It'll be terrible. You should never get a Westwater Permit this time of year unless you want a good opportunity to break up with your woman by putting her through post-season boating hell. Your best bet is to go ahead and cancel your permit tomorrow am so some masochistic idiot can go on the canyon instead, or, better yet, make someone else your alternate TL.
I'll PM you with my full name and address so you can do just that because I really hate beautiful sunny weather in the 70s and only go boating when it's horrible out.
Here's what the weather will be like at Little Dolores campsite
Here's what the water temparature will be
, along with the flow. You'll notice that it's recently dropped from about 68 to 60 degrees. I wouldn't want to swim in that water but I've seen it done. I highly recommend against it due to hypothermia risk. Westwater is very friendly at 5K cfs.
Based on that, I'd recommend having a windbreaker or splash top handy for the floating and running the rapids geared up for a cold swim. Splash gear should be fine, a drysuit may be overkill for some folks but when you go into the shade just after Marble Canyon Rapid, be glad you've got it on.
Have a great trip,