There will definitely be jet boats and the weather can vary quite a bit in the spring and fall down there. Its not uncommon to get rained on. The flows are usually about 9000 to 10000 in the fall but can also vary quite a bit too. I really like the canyon most any time but the fall is my favorite, some fair weather boaters prefer the super hot summer, big water folks like the spring. In the fall the flows are usually just right for fishing, the rapids are pretty easy, in comparison to spring and summer flows anyway. At about 30000 things get pretty exciting for a few seconds in Granite, Wild Sheep gets a little hairier as the flows drop, and its not so miserably hot.