In an average year in the Sierra,
"Shorts weather" ends around Sept 10-15. (Although I have hiked in 80-degree weather around October 15. Exceptions abound.) Nights are cold. I tell my friends to bring warmer sleeping pads and clothes. But storm-wise, I have always felt pretty safe through the end of September.
Oct 1 seems to be about the time the first snow storm or two will arrive. Most are quick and melt right away.
Oct 5-10 is the date after which I get seriously concerned about my car being stranded if there is a big storm. In 2009, that very nearly happened to me on Oct. 4. A snowplow only came because a local muckity-muck whose car had also been stranded by the storm made a lot of noise. (We also lost the trail on the way back to the car...That's another story.)
The thing about hiking after Labor Day is that the crowds are gone. That means you can pick any trailhead you want in the Sierra, and just get a walk-in permit. Get a last-minute weather forecast and then plan your trip accordingly.
If there is a chance of storm, I agree that you might not (a) make your itinerary dependent on returning over a high pass (over ~10,500 feet); nor (b) park your car at a high or distant trailhead (where either the road to the trailhead, and/or the trailhead itself, goes over the ~8000-foot mark).
The period immediately following Labor Day is the BEST time all season to visit some of the spectacular spots that are very heavily used prior to Labor Day. That's my favorite time to visit places like the Ritter Range, Dusy Basin or Evolution Basin. Those locations are at 10k-12k feet, so you generally don't want to visit them too late, either (after ~Sept 20), if you mind the nights which can get very cold that high by end of September.
Roads End in Kings Canyon is a great place to go for a mid-October trip.