Utards have their own forum; Utah Rivers
April and May are generally the best season in UT.
In April the S Utah stuff starts going. Zion, San Rafael and Cottonwood creek. The lower runs on the N Provo that are the fun slides and stuff are hard to hit just right. It is high side of good for 2 weeks then drops to low side of good in 3 days. So the best is to get comfortable running it high and you get a good long season on it. The upper waterfalls are good for a month, they seem t hold the same flow even when the lower is too high. The best weekend trip is Cottonwood creek, Left Hand of Huntington and San Rafael Black boxes. Usually late April, keep an eye on the gauges. They are not on USGS, but the UTrivers page has the gauge on there.