My experience on the Henry's Fork and the South Fork of the Snake has been that during the pre-emergence, when the nymphs are crawling towards shore to molt, the fish get pretty well gorged before the adults ever start to fly. Best during the week or so before and the week or so after, with the after being the optumum time, but I've never found the "hatch" to be very reliable at all. A lot of hype, for not much. Don't get me wrong, if you can hit it just right it is the most phenominal thing you'll ever experience, but hitting it just right requires more skills, patience and crystal ball gazing than I have.

Kelly.