If you are determined to travel southbound from Yosemite this year on the JMT before the middle of September when advance permits are still available, it is possible, just a little convoluted. First, you must go to Happy Isles, get a walk-in permit, and walk to Tuolumne. Then in Tuolumne you must get another walk-in permit to go South over Donohue Pass. They give out 10 walk-in Lyell Canyon/Donohue permits a day there. No, you can't get a walk-in permit from any other trailhead to go straight through over Donohue; the Tuolumne office is the only place that allows you to get over the hill. If any walk-ins or cancellations are available on the day you arrive at the office, you can walk away with a permit at 8 am and leave that day. Otherwise they make you wait until 11 am to get a permit for the next day (provided you are amongst the first 10 people in line). This information is on their website, but may be confusing for the uninitiated- hope this helps. http://www.nps.gov/yose/planyourvisit/jmtfaq.htm
