Given the current snow pack levels, is May 19th an unreasonable start date for the JMT from Happy Isles? Planning on 10 miles a day for re-supply at Muir or Vermillion if they are open on or around May 30 to June 1. I can delay departure up to 2 weeks if advisable. Any and all advice appreciated.
JohnG, I thought some folks would have responded by now to this. I'll offer my two cents.
I suspect your biggest issues are going to be snow and creek levels. The Yosemite Valley floor is at about 4000 feet and within a few days you'll be at 9000'+ in Tuolumne Meadows. Assuming you're doing the entire JMT you'll be hitting high passes in the 12,000' - 13,000' range within a couple weeks after starting, depending on how fast you're planning on going.
Currently down in the Whitney region there's continuous snow from Lower Boyscout Lake at 10,300'. Farther north it's 9000'+. Although the forecast for now is looking sunny and warm the months of April and May can be stormy months in the Sierra.
Assuming you hit snow on the trail you can expect it to be a mix of a consolidated snowpack that's easily walked on to unconsolidated snow that gets soft by mid morning and prone to post holing sometimes over your knees and occasionally up to your hip.
It's still too early to predict how much snow will be around by mid-May but I wouldn't count on it being free of snow just yet. On a normal snow year as temperatures warm up in late May and June the snowpack seems to melt at a rate of about 500' per week.
My personal opinion would be to wait a couple weeks. The only trade off with the snowpack is the creeks may be a bit more swollen.
