2011 saw a strong La Nina ...
... and run off wasn't really over in Northern Idaho and Western Montana until almost August. I think it might have run even later in SW Montana, and South Eastern and Central Idaho had even more snow and longer run off than we did up here.
2012 will see a milder La Nina, but still a La Nina. Right now, I'm thinking run off will end a bit earlier next summer than it did this past summer. If you want to avoid run off, plan for after the first of August for the Intermountain West to include Idaho and Western / SW Montana.
On the other hand, if you are willing to work at it, you can fish during the run off, and in some places even dry fly fishing will be great then. DUB reported some great fishing during run off in Western Colorado. I put up a thread on the great fishing I had in Northern Idaho last year during run off, starting in late May just before it peaked through late July when things finally began to settle down.
John
P.S. It seems like just about everything was at least two to three weeks late this year and may well be that late again next summer - so if you are thinking about matching the hatches, take that into account.