Saximus03:
fit2climb's experiences give you a good idea of how variable it can be. It's just the luck of the draw, so watching the forecast just before you go is the best you can do. This sounds like a first-time trip, so I'd suggest you cancel if weather looks anything other than pleasant.
If I were you, I'd try to go earlier -- first two weeks in September are better chances of good weather, and the days are definitely longer. Starting mid-August, check the
recreation.gov site often, and see if you can grab a no-show or canceled permit. Some show up just a day or two before the hike date. Not sure about this year, though, since it is all on-line, and it depends on how Inyo N.F. is handling the check-in process.
If you have all your gear ready to go on short notice, this would make for a better trip.
