In mid to late June the NOBOers doing thru-hikes this year will be postholing a much larger percentage of the day's mileage than would be true in more 'normal' years. That will be a physical challenge. Sadly for them, this mega-snow situation is not confined to the Sierras. All the western mountains seem to have well-above-average snows.

btw, have a great time on the JMT!