I led another Scout group through the Zion Narrows. The Backcountry Ranger told me we had better all have wet suits due to abnormally high and cold water. A bit overkill in my opinion. We wore pretty standard clothing and were certainly chilled early on, but things warmed up nicely.
If you can manage the colder temps, mid October really might me the best time for the Narrows. Fall colors were again off the charts.
Enjoy the pics: