The NWS point forecast as provided by Kent should certainly be carefully monitored and taken into consideration but not relied on exclusively; especially for advance planning where you need to consider the range of possibilities. Plus that forecast is only "good" for @ 3 to 5 days out so depending on the last chance you get to check it..... The best I can tell those forecasts are made using relatively remote data; in this case using data from Bishop and then running a formula or maybe the term ought to be logarithm to compensate for the difference in elevation and maybe even humidity. Also depending on the prevailing big picture weather pattern, that forecast can turn on a dime beyond about 72 hours out; sometimes if there are a lot of factors, fronts, patterns in the balance even quicker.
Are there big fronts and "closed"lows in the "picture" or is the longer range pretty much all highs? If the long range pattern has few "wild cards" then the forecast is more reliable. This is a link to the longer range models with the second model listed the gfs,(one of several models the NWS typically uses to make forecasts) showing the model projections out @ 16 days. Generally speaking these can be wildly inaccurate beyond that 72 hour margin BUT you can at least get an idea if there are wild cards in the overall pattern. The weather channel also has a 10 day forecast. Very simplistically speaking look for highs dominating the map and no colors beyond the light green and green. If there's a low with lots of concentric circles (closed low) and blues/magentas and reds associated shown passing anywhere near your destination that would constitute a wild card!
But even then you need, as you are doing, to plan for the range of possibilities.
The nearest data point with years of historical NWS data at the most comparable elevation (@ 8000') I've been able to find is Mammoth or Mammoth Lakes. You can search for that on the weather channel site and get the long term daily averages and records.
Does anyone else know of another site nearer than Mammoth or with comparable elevations and daily historical data? I can't find a good one but I don't know much about Ca. weather.