Out West Again

I know it's a little off topic right now with all the JJII buzz but unlike my ole lady I like to plan ahead and try to make a plan.

Next spring we will be headed back out west for 2 weeks with the main focus on Yellowstone and Colorado then a side trip to AZ to visit my daughter. My first thought was just jump in the truck and drive but that would put us 9 days on the road... Now we are looking to possibly flying into Las Vegas (cheap air fare) and truckin' it from there up to MT. then down to AZ.

I guess after this long intro I'm asking for info as to best times within my scope, fishing and off tourist. This year we went to the Grand Canyon in mid March and it was perfect...
What I have open is April through Mid May then sometime after mid June(which I think is tourist time). I know nothing of Montana and only the GD from Colorado so I don't care about a little snow but don't want footage. Also I read Mid may can produce lots of runoff and blow waters out.

Can anyone tell me when a good time to go there is durring those times (early or later) or is it just a crap shoot then ?
I may also inquire later for some intel on fishin' holes

Thanks.....

Tuna, from my few stints living in CO, I can tell you one thing the locals used to tell me. "If you don't like the weather, wait 15 minutes". I do know of some prime fly fishing waters in Summit County, specifically the Blue and Snake Rivers.  And if you're in the mood for walleye, I can point you to 2 waters not too far from Denver with good populations of nice sized 'eyes. I forget the names of them right now, but can find them looking at a map. I'll be out there in just over a month myself. Can't wait!!!