Base your Eastern Sierra fishing trip on snowpack.

A few couple years ago, my late July run to the Eastern Sierra featured ideal conditions in terms of water conditions in lakes, water flows in creeks and backcountry access. Keeping this in mind, I made sure to schedule last season’s run during the same time of year. Little did I know at the time I made the reservation, the area was blanketed with enough snowfall in the winter that people we still skiing through the 4th of July. The lesson here is, no matter what conditions you prefer when visiting the Eastern Sierra seeking trout or otherwise, it’s best to gauge the dates of the visit based on the snowpack.
Generally speaking, more snow is a good thing. A good snow pack ensures fishable conditions in the creeks later in the season when precipitation is minimal, and it recharges area aquifers which supply the spring fed creeks and rivers including the mighty Owens. Not to mention, much of the state’s domestic water supply depends on how much snow the Sierra Nevada range got that season.
However, heavy snowpack could adversely affect your trip in a variety of ways if you go too early. Even last summer when I spent a week in the Mammoth area in July, there was still a ton of snow in the Mammoth Lakes Basin to the point where Volkswagen-sized chunks were breaking off into the lake as we fished the shore of Lake Mary, and even if you could get to Lake George, it was unfishable. There were no backcountry options (the bread-and-butter of my trips) because the trails were still buried in snow, and even if you could get to the closer high-country lakes, they were either just beginning to thaw, or at higher elevations, still completely frozen. The road to my favorite area — Saddlebag Lake and the 20 Lakes Basin — was also closed due to snow.
While I had decent success fishing the lower level drive-up lakes, I spent way more time at them than I usually do as a result of essentially not being able to fish creeks or get into the backcountry. Speaking specifically for last summer, a mid-to-late August trip would have been ideal.
While there can never be a hard formula for determining the conditions in the Sierra Nevada mountains — especially if you are making reservations months ahead of time — monitoring the early-season snowpack is a big step in the right direction in terms of increasing your odds of getting up there and finding the conditions you are looking for.