Walter just posted an in-depth snowpack and runoff report and an outlook for summer streamflows and fishing over at Yellowstone Country Fly Fishing. Rather than reinvent the wheel, we suggest you click this link for the details.
Long story short, we have low snowpack and runoff is near its peak. We anticipate a low runoff, an early end to runoff, and low, warm streamflows this summer. In general the best opportunities will be in the first three weeks of July before things drop too much, though after that the fishing will still be good as long as it’s not super hot and dry. If it IS super hot and dry… well, we might be doing a lot of 6AM to 2PM trips and morning half-days.